NASA Astrophysics Data System (ADS)
Hanson-Heine, Magnus W. D.
2015-10-01
Carefully choosing a set of optimized coordinates for performing vibrational frequency calculations can significantly reduce the anharmonic correlation energy from the self-consistent field treatment of molecular vibrations. However, moving away from normal coordinates also introduces an additional source of correlation energy arising from mode-coupling at the harmonic level. The impact of this new component of the vibrational energy is examined for a range of molecules, and a method is proposed for correcting the resulting self-consistent field frequencies by adding the full coupling energy from connected pairs of harmonic and pseudoharmonic modes, termed vibrational self-consistent field (harmonic correlation). This approach is found to lift the vibrational degeneracies arising from coordinate optimization and provides better agreement with experimental and benchmark frequencies than uncorrected vibrational self-consistent field theory without relying on traditional correlated methods.
Miliordos, Evangelos; Xantheas, Sotiris S.
2013-08-15
We propose a general procedure for the numerical calculation of the harmonic vibrational frequencies that is based on internal coordinates and Wilson’s GF methodology via double differentiation of the energy. The internal coordinates are defined as the geometrical parameters of a Z-matrix structure, thus avoiding issues related to their redundancy. Linear arrangements of atoms are described with a dummy atom of infinite mass. The procedure has been automated in FORTRAN90 and its main advantage lies in the nontrivial reduction of the number of single point energy calculations needed for the construction of the Hessian matrix when compared to the corresponding number using double differentiation in Cartesian coordinates. For molecules of C1 symmetry the computational savings amount to 36! − 30, where N is the number of atoms, with additional savings when symmetry is present. Typical applications for small and medium size molecules in their minimum and transition state geometries as well as hydrogen bonded clusters are presented. In all cases the frequencies based on internal coordinates differ on average by < 1 cm-1 from those obtained from Cartesian coordinates.
Sebastian, S; Sylvestre, S; Jayarajan, D; Amalanathan, M; Oudayakumar, K; Gnanapoongothai, T; Jayavarthanan, T
2013-01-15
In this work, we report harmonic vibrational frequencies, molecular structure, NBO and HOMO, LUMO analysis of Umbelliferone also known as 7-hydroxycoumarin (7HC). The optimized geometric bond lengths and bond angles obtained by computation (monomer and dimmer) shows good agreement with experimental XRD data. Harmonic frequencies of 7HC were determined and analyzed by DFT utilizing 6-311+G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of Normal Coordinate Analysis (NCA) following the Scaled Quantum Mechanical Force Field Methodology (SQMFF). The change in electron density (ED) in the ?* and ?* antibonding orbitals and stabilization energies E(2) have been calculated by Natural Bond Orbital (NBO) analysis to give clear evidence of stabilization originating in the hyperconjugation of hydrogen-bonded interaction. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. The simulated spectra satisfactorily coincides with the experimental spectra. Microbial activity of studied compounds was tested against Staphylococcus aureus, Streptococcus pyogenes, Bacillus subtilis, Escherichia coli, Psuedomonas aeruginosa, Klebsiella pneumoniae, Proteus mirabilis, Shigella flexneri, Salmonella typhi and Enterococcus faecalis. PMID:23123244
NASA Astrophysics Data System (ADS)
Sebastian, S.; Sylvestre, S.; Jayarajan, D.; Amalanathan, M.; Oudayakumar, K.; Gnanapoongothai, T.; Jayavarthanan, T.
2013-01-01
In this work, we report harmonic vibrational frequencies, molecular structure, NBO and HOMO, LUMO analysis of Umbelliferone also known as 7-hydroxycoumarin (7HC). The optimized geometric bond lengths and bond angles obtained by computation (monomer and dimmer) shows good agreement with experimental XRD data. Harmonic frequencies of 7HC were determined and analyzed by DFT utilizing 6-311+G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of Normal Coordinate Analysis (NCA) following the Scaled Quantum Mechanical Force Field Methodology (SQMFF). The change in electron density (ED) in the σ* and π* antibonding orbitals and stabilization energies E(2) have been calculated by Natural Bond Orbital (NBO) analysis to give clear evidence of stabilization originating in the hyperconjugation of hydrogen-bonded interaction. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. The simulated spectra satisfactorily coincides with the experimental spectra. Microbial activity of studied compounds was tested against Staphylococcus aureus, Streptococcus pyogenes, Bacillus subtilis, Escherichia coli, Psuedomonas aeruginosa, Klebsiella pneumoniae, Proteus mirabilis, Shigella flexneri, Salmonella typhi and Enterococcus faecalis.
Application of higher harmonic blade feathering for helicopter vibration reduction
NASA Technical Reports Server (NTRS)
Powers, R. W.
1978-01-01
Higher harmonic blade feathering for helicopter vibration reduction is considered. Recent wind tunnel tests confirmed the effectiveness of higher harmonic control in reducing articulated rotor vibratory hub loads. Several predictive analyses developed in support of the NASA program were shown to be capable of calculating single harmonic control inputs required to minimize a single 4P hub response. In addition, a multiple-input, multiple-output harmonic control predictive analysis was developed. All techniques developed thus far obtain a solution by extracting empirical transfer functions from sampled data. Algorithm data sampling and processing requirements are minimal to encourage adaptive control system application of such techniques in a flight environment.
NASA Astrophysics Data System (ADS)
Hussein, M. F. M.; Hunt, H. E. M.
2009-03-01
This paper presents a new method for modelling floating-slab tracks with discontinuous slabs in underground railway tunnels. The track is subjected to a harmonic load moving with a constant velocity. The model consists of two sub-models. The first is an infinite track with periodic double-beam unit formulated as a periodic infinite structure. The second is modelled with a new version of the Pipe-in-Pipe (PiP) model that accounts for a tunnel wall embedded in a half-space. The two sub-models are coupled by writing the force transmitted from the track to the tunnel as a continuous function using Fourier series representation and satisfying the compatibility condition. The displacements at the free surface are calculated for a track with discontinuous slab and compared with those of a track with continuous slab. The results show that the far-field vibration can be significantly increased due to resonance frequencies of slabs for tracks with discontinuous slabs.
Tiltrotor Vibration Reduction Through Higher Harmonic Control
NASA Technical Reports Server (NTRS)
Nixon, Mark W.; Kvaternik, Raymond G.; Settle, T. Ben
1997-01-01
The results of a joint NASA/Army/Bell Helicopter Textron wind-tunnel test to assess the potential of higher harmonic control (HHC) for reducing vibrations in tiltrotor aircraft operating in the airplane mode of flight, and to evaluate the effectiveness of a Bell-developed HHC algorithm called MAVSS (Multipoint Adaptive Vibration Suppression System) are presented. The test was conducted in the Langley Transonic Dynamics Tunnel using an unpowered 1/5-scale semispan aeroelastic model of the V-22 which was modified to incorporate an HHC system employing both the rotor swashplate and the wing flaperon. The effectiveness of the swashplate and the flaperon acting either singly or in combination in reducing IP and 3P wing vibrations over a wide range of tunnel airspeeds and rotor rotational speeds was demonstrated. The MAVSS algorithm was found to be robust to variations in tunnel airspeed and rotor speed, requiring only occasional on-line recalculations of the system transfer matrix. HHC had only a small (usually beneficial) effect on blade loads but increased pitch link loads by 25%. No degradation in aeroelastic stability was noted for any of the conditions tested.
Higher Harmonic Control for Tiltrotor Vibration Reduction
NASA Technical Reports Server (NTRS)
Nixon, Mark W.; Kvaternik, Raymond G.; Settle, T. Ben
1997-01-01
The results of a joint NASA/Army/Bell Helicopter Textron wind-tunnel test to assess the potential of higher harmonic control (HHC) for reducing vibrations in tiltrotor aircraft operating in the airplane mode of flight, and to evaluate the effectiveness of a Bell-developed HHC algorithm called MAVSS (Multipoint Adaptive Vibration Suppression System) are presented. The test was conducted in the Langley Transonic Dynamics Tunnel using an unpowered 1/5- scale semispan aeroelastic model of the V-22 which was modified to incorporate an HHC system employing both the rotor swashplate and the wing flaperon. The effectiveness of the swashplate and the flaperon acting either singly or in combination in reducing 1P and 3P wing vibrations over a wide range of tunnel airspeeds and rotor rotational speeds was demonstrated. The MAVSS algorithm was found to be robust to variations in tunnel airspeed and rotor speed, requiring only occasion-al on-line recalculations of the system transfer matrix.
Harmonic Debye-Waller analysis of anharmonic vibrations
NASA Astrophysics Data System (ADS)
Safarik, D. J.; Llobet, A.; Lashley, J. C.
2012-05-01
We address the error resulting from application of the harmonic Debye-Waller factor to anharmonic vibrations. The mean-square atomic displacement
NASA Technical Reports Server (NTRS)
Holliday, Ezekiel S. (Inventor)
2014-01-01
Vibrations of a principal machine are reduced at the fundamental and harmonic frequencies by driving the drive motor of an active balancer with balancing signals at the fundamental and selected harmonics. Vibrations are sensed to provide a signal representing the mechanical vibrations. A balancing signal generator for the fundamental and for each selected harmonic processes the sensed vibration signal with adaptive filter algorithms of adaptive filters for each frequency to generate a balancing signal for each frequency. Reference inputs for each frequency are applied to the adaptive filter algorithms of each balancing signal generator at the frequency assigned to the generator. The harmonic balancing signals for all of the frequencies are summed and applied to drive the drive motor. The harmonic balancing signals drive the drive motor with a drive voltage component in opposition to the vibration at each frequency.
Index calculation by means of harmonic expansion
NASA Astrophysics Data System (ADS)
Imamura, Yosuke
2015-11-01
We review derivation of superconformal indices by means of supersymmetric localization and spherical harmonic expansion for 3d mathcal {N}=2, 4d mathcal {N}=1, and 6d mathcal {N}=(1,0) supersymmetric gauge theories. We demonstrate calculation of indices for vector multiplets in each dimension by analyzing energy eigenmodes in {boldsymbol S}^p × mathbb {R}. For the 6d index we consider the perturbative contribution only. We focus on the technical details of harmonic expansion rather than physical applications.
ERIC Educational Resources Information Center
Parnis, J. Mark; Thompson, Matthew G. K.
2004-01-01
An introductory undergraduate physical organic chemistry exercise that introduces the harmonic oscillator's use in vibrational spectroscopy is developed. The analysis and modeling exercise begins with the students calculating the stretching modes of common organic molecules with the help of the quantum mechanical harmonic oscillator (QMHO) model.
Calculating Ro-Vibrational Spectra of Van Der Waals Molecules
NASA Astrophysics Data System (ADS)
Wang, Xiaogang; Carrington, Tucker, Jr.
2010-06-01
Van der Waals molecules are loosely bound and strongly coupled and their spectroscopy can therefore not be understood with a rigid rotor + harmonic oscillator model. Useful insight can be obtained by numerically solving the ro-vibrational Schroedinger equation using a basis set. The most obvious impediment is the size of the basis required to obtain converged results. Nonetheless, by using an iterative eigensolver and exploiting the structure of quadrature approximations for potential matrix elements, it is possible to do calculations for many molecules of interest. I shall discuss how the choice of the vibrational coordinates and the molecule-fixed axis system influence the calculation of ro-vibrational spectra of Van der Waals molecules and present new results for (NNO)_2, H_2-H_2O, and SF_6-He_2.
Vibrational spectroscopy and relaxation of an anharmonic oscillator coupled to harmonic bath
NASA Astrophysics Data System (ADS)
Joutsuka, Tatsuya; Ando, Koji
2011-05-01
The vibrational spectroscopy and relaxation of an anharmonic oscillator coupled to a harmonic bath are examined to assess the applicability of the time correlation function (TCF), the response function, and the semiclassical frequency modulation (SFM) model to the calculation of infrared (IR) spectra. These three approaches are often used in connection with the molecular dynamics simulations but have not been compared in detail. We also analyze the vibrational energy relaxation (VER), which determines the line shape and is itself a pivotal process in energy transport. The IR spectra and VER are calculated using the generalized Langevin equation (GLE), the Gaussian wavepacket (GWP) method, and the quantum master equation (QME). By calculating the vibrational frequency TCF, a detailed analysis of the frequency fluctuation and correlation time of the model is provided. The peak amplitude and width in the IR spectra calculated by the GLE with the harmonic quantum correction are shown to agree well with those by the QME though the vibrational frequency is generally overestimated. The GWP method improves the peak position by considering the zero-point energy and the anharmonicity although the red-shift slightly overshoots the QME reference. The GWP also yields an extra peak in the higher-frequency region than the fundamental transition arising from the difference frequency of the center and width oscillations of a wavepacket. The SFM approach underestimates the peak amplitude of the IR spectra but well reproduces the peak width. Further, the dependence of the VER rate on the strength of an excitation pulse is discussed.
NASA Technical Reports Server (NTRS)
Holliday, Ezekiel S. (Inventor)
2014-01-01
Vibrations at harmonic frequencies are reduced by injecting harmonic balancing signals into the armature of a linear motor/alternator coupled to a Stirling machine. The vibrations are sensed to provide a signal representing the mechanical vibrations. A harmonic balancing signal is generated for selected harmonics of the operating frequency by processing the sensed vibration signal with adaptive filter algorithms of adaptive filters for each harmonic. Reference inputs for each harmonic are applied to the adaptive filter algorithms at the frequency of the selected harmonic. The harmonic balancing signals for all of the harmonics are summed with a principal control signal. The harmonic balancing signals modify the principal electrical drive voltage and drive the motor/alternator with a drive voltage component in opposition to the vibration at each harmonic.
Effect of acoustic coupling on random and harmonic plate vibrations
NASA Technical Reports Server (NTRS)
Frendi, Abdelkader; Robinson, Jay
1993-01-01
The effect of acoustic coupling on random and harmonic plate vibrations is studied using two numerical models. In the coupled model, the plate response is obtained by integration of the nonlinear plate equation coupled with the nonlinear Euler equations for the surrounding acoustic fluid. In the uncoupled model, the nonlinear plate equation with an equivalent linear viscous damping term is integrated to obtain the response of the plate subject to the same excitation field. For a low-level, narrow-band excitation, the two models predict the same plate response spectra. As the excitation level is increased, the response power spectrum predicted by the uncoupled model becomes broader and more shifted towards the high frequencies than that obtained by the coupled model. In addition, the difference in response between the coupled and uncoupled models at high frequencies becomes larger. When a high intensity harmonic excitation is used, causing a nonlinear plate response, both models predict the same frequency content of the response. However, the level of the harmonics and subharmonics are higher for the uncoupled model. Comparisons to earlier experimental and numerical results show that acoustic coupling has a significant effect on the plate response at high excitation levels. Its absence in previous models may explain the discrepancy between predicted and measured responses.
Xu, Xiangbo; Chen, Shao
2015-01-01
Harmonic vibrations of high-speed rotors in momentum exchange devices are primary disturbances for attitude control of spacecraft. Active magnetic bearings (AMBs), offering the ability to control the AMB-rotor dynamic behaviors, are preferred in high-precision and micro-vibration applications, such as high-solution Earth observation satellites. However, undesirable harmonic displacements, currents, and vibrations also occur in the AMB-rotor system owing to the mixed rotor imbalances and sensor runout. To compensate the rotor imbalances and to suppress the harmonic vibrations, two control methods are presented. Firstly, a four degrees-of-freedom AMB-rotor model with the static imbalance, dynamic imbalance, and the sensor runout are described. Next, a synchronous current reduction approach with a variable-phase notch feedback is proposed, so that the rotor imbalances can be identified on-line through the analysis of the synchronous displacement relationships of the geometric, inertial, and rotational axes of the rotor. Then, the identified rotor imbalances, which can be represented at two prescribed balancing planes of the rotor, are compensated by discrete add-on weights whose masses are calculated in the vector form. Finally, a repetitive control algorithm is utilized to suppress the residual harmonic vibrations. The proposed field balancing and harmonic vibration suppression strategies are verified by simulations and experiments performed on a control moment gyro test rig with a rigid AMB-rotor system. Compared with existing methods, the proposed strategies do not require trial weights or an accurate model of the AMB-rotor system. Moreover, the harmonic displacements, currents, and vibrations can be well-attenuated simultaneously. PMID:26334281
Xu, Xiangbo; Chen, Shao
2015-01-01
Harmonic vibrations of high-speed rotors in momentum exchange devices are primary disturbances for attitude control of spacecraft. Active magnetic bearings (AMBs), offering the ability to control the AMB-rotor dynamic behaviors, are preferred in high-precision and micro-vibration applications, such as high-solution Earth observation satellites. However, undesirable harmonic displacements, currents, and vibrations also occur in the AMB-rotor system owing to the mixed rotor imbalances and sensor runout. To compensate the rotor imbalances and to suppress the harmonic vibrations, two control methods are presented. Firstly, a four degrees-of-freedom AMB-rotor model with the static imbalance, dynamic imbalance, and the sensor runout are described. Next, a synchronous current reduction approach with a variable-phase notch feedback is proposed, so that the rotor imbalances can be identified on-line through the analysis of the synchronous displacement relationships of the geometric, inertial, and rotational axes of the rotor. Then, the identified rotor imbalances, which can be represented at two prescribed balancing planes of the rotor, are compensated by discrete add-on weights whose masses are calculated in the vector form. Finally, a repetitive control algorithm is utilized to suppress the residual harmonic vibrations. The proposed field balancing and harmonic vibration suppression strategies are verified by simulations and experiments performed on a control moment gyro test rig with a rigid AMB-rotor system. Compared with existing methods, the proposed strategies do not require trial weights or an accurate model of the AMB-rotor system. Moreover, the harmonic displacements, currents, and vibrations can be well-attenuated simultaneously. PMID:26334281
Ab initio DFT calculations of vibrational properties
NASA Astrophysics Data System (ADS)
Story, S. M.; Vila, F. D.; Kas, J. J.; Rehr, J. J.
2014-03-01
Vibrational properties such as EXAFS and crystallographic Debye-Waller factors, vibrational free energies, phonon self-energies, and phonon contributions to the electron spectral function, are key to understanding many aspects of materials beyond ground state electronic structure. Thus, their simulation using first principles methods is of particular importance. Many of these vibrational properties can be calculated from the dynamical matrix and electron-phonon coupling coefficients obtained from DFT calculations. Here we present a code DMVP that calculates these properties from the output of electronic structure codes such as ABINIT, Gaussian, Quantum Espresso and VASP. Our modular interfacing tool AI2PS allows us to translate the different outputs into a DMVP compatible format and generate vibrational properties in an automated way. Finally, we present some current applications that take advantage of the modular form of AI2PS to extend its capabilities to the calculation of coefficients of thermal expansion and other properties of interest such as infrared spectra. This work was supported by DOE Grant DE-FG02-97ER45623.
Local ergodicity in coupled harmonic vibrators: classical and quantal treatments
NASA Astrophysics Data System (ADS)
Englman, R.
2016-03-01
Ensemble-time ergodicity is proven under some restrictive assumptions for a classical system, comprising interacting harmonic oscillators. An atom in a monatomic chain or lattice is shown to behave ergodically, in the sense that the time average behavior of a lattice point is identical to the ensemble average of the behavior of a lattice point at any long time (in large excess of the inverse vibrational frequencies). This equivalence (for ‘local observables’) differs from the Fermi–Pasta–Ulam result for mode energies (which are non-local). Then, the analogous quantal result is derived, with extensions to wider instances. Relationships to canonical typicality and to the eigenstate thermalization hypothesis are discussed and possibilities of experimental verifications of the results are indicated.
Harmonic Torque Calculation of Induction Motors Using Electromagnetic Field Analysis
NASA Astrophysics Data System (ADS)
Yamazaki, Katsumi; Haruishi, Yoshihisa; Ara, Takahiro
In this paper, we investigate effects of harmonic electromagnetic field to torque characteristics of induction motors from both side of experiment and electromagnetic field analysis. The characteristics of two kinds of the aluminum cage three-phase induction motors are measured and calculated. One is with the closed rotor slots. The other is semi-closed. In the experiment, the negative torque at synchronous speed is measured by driving the induction motor by the synchronous permanent magnet motor. The total torque at load condition is also measured by the torque detector. In the analysis, the harmonic magnetic fields, the harmonic losses and the harmonic torques at each time and space harmonic order are calculated using the nonlinear time-stepping finite element method to clarify the mechanism of the harmonic torque generation. The measured and the calculated results agree well. It is clarified that the negative torque caused by the slot harmonics at the rated load condition is not negligible and that the negative torque is mainly generated by the harmonic core losses.
Optimized coordinates in vibrational coupled cluster calculations
NASA Astrophysics Data System (ADS)
Thomsen, Bo; Yagi, Kiyoshi; Christiansen, Ove
2014-04-01
The use of variationally optimized coordinates, which minimize the vibrational self-consistent field (VSCF) ground state energy with respect to orthogonal transformations of the coordinates, has recently been shown to improve the convergence of vibrational configuration interaction (VCI) towards the exact full VCI [K. Yagi, M. Keeli, and S. Hirata, J. Chem. Phys. 137, 204118 (2012)]. The present paper proposes an incorporation of optimized coordinates into the vibrational coupled cluster (VCC), which has in the past been shown to outperform VCI in approximate calculations where similar restricted state spaces are employed in VCI and VCC. An embarrassingly parallel algorithm for variational optimization of coordinates for VSCF is implemented and the resulting coordinates and potentials are introduced into a VCC program. The performance of VCC in optimized coordinates (denoted oc-VCC) is examined through pilot applications to water, formaldehyde, and a series of water clusters (dimer, trimer, and hexamer) by comparing the calculated vibrational energy levels with those of the conventional VCC in normal coordinates and VCI in optimized coordinates. For water clusters, in particular, oc-VCC is found to gain orders of magnitude improvement in the accuracy, exemplifying that the combination of optimized coordinates localized to each monomer with the size-extensive VCC wave function provides a supreme description of systems consisting of weakly interacting sub-systems.
Optimized coordinates in vibrational coupled cluster calculations
Thomsen, Bo; Christiansen, Ove; Yagi, Kiyoshi
2014-04-21
The use of variationally optimized coordinates, which minimize the vibrational self-consistent field (VSCF) ground state energy with respect to orthogonal transformations of the coordinates, has recently been shown to improve the convergence of vibrational configuration interaction (VCI) towards the exact full VCI [K. Yagi, M. Keçeli, and S. Hirata, J. Chem. Phys. 137, 204118 (2012)]. The present paper proposes an incorporation of optimized coordinates into the vibrational coupled cluster (VCC), which has in the past been shown to outperform VCI in approximate calculations where similar restricted state spaces are employed in VCI and VCC. An embarrassingly parallel algorithm for variational optimization of coordinates for VSCF is implemented and the resulting coordinates and potentials are introduced into a VCC program. The performance of VCC in optimized coordinates (denoted oc-VCC) is examined through pilot applications to water, formaldehyde, and a series of water clusters (dimer, trimer, and hexamer) by comparing the calculated vibrational energy levels with those of the conventional VCC in normal coordinates and VCI in optimized coordinates. For water clusters, in particular, oc-VCC is found to gain orders of magnitude improvement in the accuracy, exemplifying that the combination of optimized coordinates localized to each monomer with the size-extensive VCC wave function provides a supreme description of systems consisting of weakly interacting sub-systems.
Quantum Monte Carlo Algorithms for Diagrammatic Vibrational Structure Calculations
NASA Astrophysics Data System (ADS)
Hermes, Matthew; Hirata, So
2015-06-01
Convergent hierarchies of theories for calculating many-body vibrational ground and excited-state wave functions, such as Mller-Plesset perturbation theory or coupled cluster theory, tend to rely on matrix-algebraic manipulations of large, high-dimensional arrays of anharmonic force constants, tasks which require large amounts of computer storage space and which are very difficult to implement in a parallel-scalable fashion. On the other hand, existing quantum Monte Carlo (QMC) methods for vibrational wave functions tend to lack robust techniques for obtaining excited-state energies, especially for large systems. By exploiting analytical identities for matrix elements of position operators in a harmonic oscillator basis, we have developed stochastic implementations of the size-extensive vibrational self-consistent field (MC-XVSCF) and size-extensive vibrational Mller-Plesset second-order perturbation (MC-XVMP2) theories which do not require storing the potential energy surface (PES). The programmable equations of MC-XVSCF and MC-XVMP2 take the form of a small number of high-dimensional integrals evaluated using Metropolis Monte Carlo techniques. The associated integrands require independent evaluations of only the value, not the derivatives, of the PES at many points, a task which is trivial to parallelize. However, unlike existing vibrational QMC methods, MC-XVSCF and MC-XVMP2 can calculate anharmonic frequencies directly, rather than as a small difference between two noisy total energies, and do not require user-selected coordinates or nodal surfaces. MC-XVSCF and MC-XVMP2 can also directly sample the PES in a given approximation without analytical or grid-based approximations, enabling us to quantify the errors induced by such approximations.
Nonlinear response of a harmonic diatomic molecule: Algebraic nonperturbative calculation
Recamier, Jose; Mochan, W. Luis; Maytorena, Jesus A.
2005-08-15
Even harmonic molecules display a nonlinear behavior when driven by an inhomogeneous field. We calculate the response of single harmonic molecules to a monochromatic time and space dependent electric field E(r,t) of frequency {omega} employing exact algebraic methods. We evaluate the responses at the fundamental frequency {omega} and at successive harmonics 2{omega}, 3{omega}, etc., as a function of the intensity and of the frequency of the field and compare the results with those of first and second order perturbation theory.
NASA Astrophysics Data System (ADS)
Heo, YongHwa; Kim, Kwang-joon
2015-02-01
While the vibration power for a set of harmonic force and velocity signals is well defined and known, it is not as popular yet for a set of stationary random force and velocity processes, although it can be found in some literatures. In this paper, the definition of the vibration power for a set of non-stationary random force and velocity signals will be derived for the purpose of a time-frequency analysis based on the definitions of the vibration power for the harmonic and stationary random signals. The non-stationary vibration power, defined as the short-time average of the product of the force and velocity over a given frequency range of interest, can be calculated by three methods: the Wigner-Ville distribution, the short-time Fourier transform, and the harmonic wavelet transform. The latter method is selected in this paper because band-pass filtering can be done without phase distortions, and the frequency ranges can be chosen very flexibly for the time-frequency analysis. Three algorithms for the time-frequency analysis of the non-stationary vibration power using the harmonic wavelet transform are discussed. The first is an algorithm for computation according to the full definition, while the others are approximate. Noting that the force and velocity decomposed into frequency ranges of interest by the harmonic wavelet transform are constructed with coefficients and basis functions, for the second algorithm, it is suggested to prepare a table of time integrals of the product of the basis functions in advance, which are independent of the signals under analysis. How to prepare and utilize the integral table are presented. The third algorithm is based on an evolutionary spectrum. Applications of the algorithms to the time-frequency analysis of the vibration power transmitted from an excitation source to a receiver structure in a simple mechanical system consisting of a cantilever beam and a reaction wheel are presented for illustration.
NASA Astrophysics Data System (ADS)
Guo, Jing; Ge, Xin-Lei; Zhong, Huiying; Zhao, Xi; Zhang, Meixia; Jiang, Yuanfei; Liu, Xue-Shen
2014-11-01
The high-order-harmonic generation (HHG) from the N2 molecule in an intense laser field is investigated by applying the Lewenstein method. The initial state is constructed as a linear combination of the highest occupied molecular orbital (HOMO) and the lower-lying orbital below the HOMO, which is well described by a Gaussian wave packet generated by using the gamess-uk package. The HHG with different vibrational states of N2 are calculated and our results show that the harmonic intensity can be enhanced by higher vibrational states, which can be explained by the ionization probability. We also compared the cases with a different full width at half maximum of laser fields together, which can be well understood by the time-frequency analysis and the three-step model. Finally, the attosecond pulse generation is studied with different vibrational states, where a series of attosecond pulses can be produced with the shortest being 91 as.
Schneider, W.; Thiel, W. ); Komornicki, A. )
1990-04-05
Ab initio self-consistent-field calculations using effective core potentials and polarized double-zeta basis sets are reported for the arsenic compounds H{sub 3}As, H{sub 3}AsO, H{sub 3}AsS, F{sub 3}As, F{sub 3}AsO, F{sub 3}AsS, cis- and trans-H{sub 2}AsOH, and HAsO. The calculated geometries, rotational constants, vibrational frequencies, Coriolis coupling constants, centrifugal distortion constants, infrared band intensities, and force fields are compared with the available experimental data. Good agreement is found in the case of the known molecules, especially H{sub 3}As and F{sub 3}As, so that the predictions for the unknown molecules are expected to be realistic. The theoretical results confirm a recent spectroscopic identification of H{sub 3}AsO, H{sub 2}AsOH, and HAsO and suggest reassignment of several observed frequencies.
Toward large scale vibrational configuration interaction calculations
NASA Astrophysics Data System (ADS)
Neff, Michael; Rauhut, Guntram
2009-09-01
The implementation of a state-specific configuration-selective vibrational configuration interaction (cs-VCI) approach based on a polynomial representation of the potential energy surface is presented. Advantages over grid-based algorithms are discussed. A combination of a configuration selection criterion, the simultaneous exclusion of irrelevant configurations, and an internal contraction scheme allow to handle large variational spaces. A modified version of the iterative Jacobi-Davidson diagonalization has been used to determine relevant internal eigenpairs of the cs-VCI matrices in the selected space. Benchmark calculations are provided for systems with up to 2107 configurations and three-mode couplings in the expansion of the potential.
Breuer, G D; Chow, J H; Lindh, C B; Miller, N W; Numrich, F H; Price, W W; Turner, A E; Whitney, R R
1982-09-01
Improved methods are needed to characterize ac system harmonic behavior for ac filter design for HVDC systems. The purpose of this General Electric Company RP1138 research is to evaluate the present filter design practice and to investigate methods for calculating system harmonic impedances. An overview of ac filter design for HVDC systems and a survey of literature related to filter design have been performed. Two methods for calculating system harmonic impedances have been investigated. In the measurement method, an instrumentation system for measuring system voltage and current has been assembled. Different schemes of using the measurements to calculate system harmonic impedances have been studied. In the analytical method, a procedure to include various operating conditions has been proposed. Computer programs for both methods have been prepared, and the results of the measurement and analytical methods analyzed. A conclusion of the project is that the measurement and analytical methods both provided reasonable results. There are correlations between the measured and analytical results for most harmonics, although there are discrepancies between the assumptions used in the two methods. A sensitivity approach has been proposed to further correlate the results. From the results of the analysis, it is recommended that both methods should be tested further. For the measurement method, more testing should be done to cover different system operating conditions. In the analytical method, more detailed models for representing system components should be studied. In addition, alternative statistical and sensitivity approaches should be attempted.
Coupled rotor-flexible fuselage vibration reduction using open loop higher harmonic control
NASA Technical Reports Server (NTRS)
Papavassiliou, I.; Friedmann, P. P.; Venkatesan, C.
1991-01-01
A fundamental study of vibration prediction and vibration reduction in helicopters using active controls was performed. The nonlinear equations of motion for a coupled rotor/flexible fuselage system have been derived using computer algebra on a special purpose symbolic computer facility. The trim state and vibratory response of the helicopter are obtained in a single pass by applying the harmonic balance technique and simultaneously satisfying the trim and the vibratory response of the helicopter for all rotor and fuselage degrees of freedom. The influence of the fuselage flexibility on the vibratory response is studied. It is shown that the conventional single frequency higher harmonic control is capable of reducing either the hub loads or only the fuselage vibrations but not both simultaneously. It is demonstrated that for simultaneous reduction of hub shears and fuselae vibrations a new scheme called multiple higher harmonic control is required.
High-order harmonic transient grating spectroscopy of SF6 molecular vibrations
NASA Astrophysics Data System (ADS)
Ferr, Amlie; Staedter, David; Burgy, Frdric; Dagan, Michal; Descamps, Dominique; Dudovich, Nirit; Petit, Stphane; Soifer, Hadas; Blanchet, Valrie; Mairesse, Yann
2014-06-01
Strong field transient grating spectroscopy has shown to be a very versatile tool in time-resolved molecular spectroscopy. Here we use this technique to investigate the high-order harmonic generation from SF6 molecules vibrationally excited by impulsive stimulated Raman scattering. Transient grating spectroscopy enables us to reveal clear modulations of the harmonic emission. This heterodyne detection shows that the harmonic emission generated between 14 and 26 eV is mainly sensitive to two among the three active Raman modes in SF6, i.e. the strongest and fully symmetric ?1-A1g mode (774 cm-1, 43 fs) and the slowest mode ?5-T2g (524 cm-1, 63 fs). A time-frequency analysis of the harmonic emission reveals additional dynamics: the strength and central frequency of the ?1 mode oscillate with a frequency of 52 cm-1 (640 fs). This could be a signature of the vibration of dimers in the generating medium. Harmonic 11 shows a remarkable behaviour, oscillating in the opposite phase, both on the fast (774 cm-1) and slow (52 cm-1) timescales, which indicates a strong modulation of the recombination matrix element as a function of the nuclear geometry. These results demonstrate that the high sensitivity of high-order harmonic generation to molecular vibrations, associated to the high sensitivity of transient grating spectroscopy, make their combination a unique tool to probe vibrational dynamics.
Application of higher harmonic blade feathering on the OH-6A helicopter for vibration reduction
NASA Technical Reports Server (NTRS)
Straub, F. K.; Byrns, E. V., Jr.
1986-01-01
The design, implementation, and flight test results of higher harmonic blade feathering for vibration reduction on the OH-6A helicopter are described. The higher harmonic control (HHC) system superimposes fourth harmonic inputs upon the stationary swashplate. These inputs are transformed into 3P, 4P and 5P blade feathering angles. This results in modified blade loads and reduced fuselage vibrations. The primary elements of this adaptive vibration suppression system are: (1) acceleration transducers sensing the vibratory response of the fuselage; (2) a higher harmonic blade pitch actuator system; (3) a flightworthy microcomputer, incorporating the algorithm for reducing vibrations, and (4) a signal conditioning system, interfacing between the sensors, the microcomputer and the HHC actuators. The program consisted of three distinct phases. First, the HHC system was designed and implemented on the MDHC OH-6A helicopter. Then, the open loop, or manual controlled, flight tests were performed, and finally, the closed loop adaptive control system was tested. In 1983, one portion of the closed loop testing was performed, and in 1984, additional closed loop tests were conducted with improved software. With the HHC system engaged, the 4P pilot seat vibration levels were significantly lower than the baseline ON-6A levels. Moreover, the system did not adversely affect blade loads or helicopter performance. In conclusion, this successful proof of concept project demonstrated HHC to be a viable vibration suppression mechanism.
Variational nodal perturbation calculations using simplified spherical harmonics
Laurin-Kovitz, K.; Palmiotti, G.; Lewis, E.E.
1996-12-31
The simplified spherical harmonics (SP{sub N}) method has been used as an approximation to the transport equation in a number of situations. Recently, the SP{sub N} method has been formulated within the framework of the variational nodal method (VNM). Implementation in the VARIANT code indicated that for many two and three dimensional problems, near P{sub N} accuracy can be obtained at a fraction of the Cost. Perturbation methods offer additional computational cost reduction for reactor core calculations and are indispensable for performing a variety of calculations including sensitivity studies and the breakdown by components of reactivity worths. Here, we extend the perturbation method developed for the VNM in the full P{sub N} approximation to treat simplified spherical harmonics. The change in reactivity predicted by both first order and exact perturbation theory using the SP{sub N} approximation is demonstrated for a benchmark problem and compared to diffusion and full P{sub N} estimates.
NASA Astrophysics Data System (ADS)
Christiansen, Ove; Luis, Josep M.
A number of different methods for calculation of vibrational energies are reviewed and tested for calculation of the fundamental vibrational frequencies for ethylene. The methods tested for the description of the vibrational states are vibrational self-consistent field (VSCF), vibrational configuration interaction (VCI), vibrational Mller-Plesset theory (VMP), and vibrational coupled cluster (VCC). The convergence of the different methods toward the full vibrational configuration interaction (FVCI) result is discussed for a modest-sized one-mode basis. For larger one-mode basis sets results are presented for selected methods. Different representations of the potential energy surface are compared including full and partial quartic force field as well as expansions using up to sixth derivatives of the potential energy surface. Using MP2 electronic structure theory, the electronic structure basis set convergence is tested.
Calculation of oscillations generated by a vibrator in a boundary layer of an incompressible fluid
NASA Astrophysics Data System (ADS)
Manuilovich, S. V.
Consideration is given to the problem of the excitation of small oscillations in flow of a viscous incompressible fluid by a vibrator generationg harmonic oscillations at the bottom of the boundary layer. The well posedness of the problem for a linearized system of Navier-Stokes equations is investigated by the Fourier method. An asymptotic analysis of the perturbed flow downstream makes it possible to determine the amplitude of the generated Tollmien-Schlichting wave. Calculations are made of the perturbation pressure in the vicinity of the vibrator.
Bulychev, Valentin P; Buturlimova, Marina V; Tokhadze, Konstantin G
2013-09-19
The equilibrium geometry of the NH3trans-HONO complex and the harmonic vibrational frequencies and intensities are calculated in the MP2/aug-cc-pVTZ approximation with the basis set superposition error taken into account. Effects of anharmonic interactions on spectroscopic parameters are studied by solving vibrational Schrdinger equations in 1-4 dimensions using the variational method. Anharmonic vibrational equations are formulated in the space of normal coordinates of the complex. Detailed analysis is performed for the H-bond stretching vibration and internal vibrations of the trans-HONO isomer in the complex. The intermode anharmonicity and anharmonic coupling between two, three, and four vibrational modes are studied on the basis of correct ab initio potential energy surfaces calculated in the above approximation. The combinations of normal modes of the complex most strongly coupled to one another are examined. The calculated frequencies and intensities of vibrational bands are compared with the experimental data on the NH3trans-HONO complex in an argon matrix and results of earlier calculations of monomeric HONO. In this calculation the strong resonance between the first excited state of the OH stretching vibration and the doubly excited state of the NOH bending vibration of trans-HONO isomer in the complex is thoroughly studied by solving vibrational equations in two and four dimensions. PMID:23944642
Tang, Gang; Hou, Wei; Wang, Huaqing; Luo, Ganggang; Ma, Jianwei
2015-01-01
The Shannon sampling principle requires substantial amounts of data to ensure the accuracy of on-line monitoring of roller bearing fault signals. Challenges are often encountered as a result of the cumbersome data monitoring, thus a novel method focused on compressed vibration signals for detecting roller bearing faults is developed in this study. Considering that harmonics often represent the fault characteristic frequencies in vibration signals, a compressive sensing frame of characteristic harmonics is proposed to detect bearing faults. A compressed vibration signal is first acquired from a sensing matrix with information preserved through a well-designed sampling strategy. A reconstruction process of the under-sampled vibration signal is then pursued as attempts are conducted to detect the characteristic harmonics from sparse measurements through a compressive matching pursuit strategy. In the proposed method bearing fault features depend on the existence of characteristic harmonics, as typically detected directly from compressed data far before reconstruction completion. The process of sampling and detection may then be performed simultaneously without complete recovery of the under-sampled signals. The effectiveness of the proposed method is validated by simulations and experiments. PMID:26473858
Tang, Gang; Hou, Wei; Wang, Huaqing; Luo, Ganggang; Ma, Jianwei
2015-01-01
The Shannon sampling principle requires substantial amounts of data to ensure the accuracy of on-line monitoring of roller bearing fault signals. Challenges are often encountered as a result of the cumbersome data monitoring, thus a novel method focused on compressed vibration signals for detecting roller bearing faults is developed in this study. Considering that harmonics often represent the fault characteristic frequencies in vibration signals, a compressive sensing frame of characteristic harmonics is proposed to detect bearing faults. A compressed vibration signal is first acquired from a sensing matrix with information preserved through a well-designed sampling strategy. A reconstruction process of the under-sampled vibration signal is then pursued as attempts are conducted to detect the characteristic harmonics from sparse measurements through a compressive matching pursuit strategy. In the proposed method bearing fault features depend on the existence of characteristic harmonics, as typically detected directly from compressed data far before reconstruction completion. The process of sampling and detection may then be performed simultaneously without complete recovery of the under-sampled signals. The effectiveness of the proposed method is validated by simulations and experiments. PMID:26473858
NASA Astrophysics Data System (ADS)
Huang, Yong-Yi
2015-11-01
We study the entanglement dynamics of the two two-level atoms coupled with a single-mode polarized cavity field after incorporating the decoupled atomic centers of mass classical harmonic vibrations with micro amplitudes and low frequencies. We discover a new quantum mechanical measurement effect for the entanglement dynamics. We propose a quantitative vibrant factor to modify the concurrence of the two atomic states. When the vibrant frequencies are very low, we obtain that: (1) the factor depends on the relative vibrant displacements and the initial phases rather than the absolute amplitudes, and reduces the concurrence to three orders of magnitude; (2) the concurrence increases with the increase of the initial phases; (3) the frequency of the harmonic vibration can be obtained by measuring the maximal value of the concurrence during a small measurement time. These results indicate that the extremely weak classical harmonic vibrations can be monitored by the entanglement of quantum states. The effect reported in the paper always works well as long as the internal degrees of freedom of the system (regardless of unitary evolution or non-unitary evolution with time) are decoupled with the external classical harmonic vibrations of atomic centers of mass.
Vibrational assignments and electronic structure calculations for 3-acetylcoumarin
NASA Astrophysics Data System (ADS)
Ramoji, Anuradha; Yenagi, Jayashree; Tonannavar, J.; Jadhav, V. B.; Kulkarni, M. V.
2007-11-01
Laser Raman (3500-50 cm -1) and IR (4000-400 cm -1) spectral measurements have been made on the laboratory prepared solid 3-acetylcoumarin. Molecular electronic energy, equilibrium geometrical structure and harmonic vibrational spectra have been computed at the RHF/6-31G(d,p) and B3LYP/6-31G(d,p) levels of theory. A complete vibrational assignment aided by the theoretical harmonic frequency analysis has been proposed. The B3LYP/6-31G(d,p) geometrical parameters, and frequencies of the C dbnd O in the pyrone and acetyl group are in good agreement with experiment. The difference in the frequencies due to the two carbonyl groups, 50 cm -1, which is attributed to the conjugation effect, is accounted for by the B3LYP to be 56 cm -1.
Cryns, Jackson W.; Hatchell, Brian K.; Santiago-Rojas, Emiliano; Silvers, Kurt L.
2013-07-01
Formal journal article Experimental analysis of a piezoelectric energy harvesting system for harmonic, random, and sine on random vibration Abstract: Harvesting power with a piezoelectric vibration powered generator using a full-wave rectifier conditioning circuit is experimentally compared for varying sinusoidal, random and sine on random (SOR) input vibration scenarios. Additionally, the implications of source vibration characteristics on harvester design are discussed. Studies in vibration harvesting have yielded numerous alternatives for harvesting electrical energy from vibrations but piezoceramics arose as the most compact, energy dense means of energy transduction. The rise in popularity of harvesting energy from ambient vibrations has made piezoelectric generators commercially available. Much of the available literature focuses on maximizing harvested power through nonlinear processing circuits that require accurate knowledge of generator internal mechanical and electrical characteristics and idealization of the input vibration source, which cannot be assumed in general application. In this manuscript, variations in source vibration and load resistance are explored for a commercially available piezoelectric generator. We characterize the source vibration by its acceleration response for repeatability and transcription to general application. The results agree with numerical and theoretical predictions for in previous literature that load optimal resistance varies with transducer natural frequency and source type, and the findings demonstrate that significant gains are seen with lower tuned transducer natural frequencies for similar source amplitudes. Going beyond idealized steady state sinusoidal and simplified random vibration input, SOR testing allows for more accurate representation of real world ambient vibration. It is shown that characteristic interactions from more complex vibrational sources significantly alter power generation and power processing requirements by increasing harvested power, shifting optimal conditioning impedance, inducing significant voltage supply fluctuations and ultimately rendering idealized sinusoidal and random analyses insufficient.
Ferré, A.; Boguslavskiy, A. E.; Dagan, M.; Blanchet, V.; Bruner, B. D.; Burgy, F.; Camper, A.; Descamps, D.; Fabre, B.; Fedorov, N.; Gaudin, J.; Geoffroy, G.; Mikosch, J.; Patchkovskii, S.; Petit, S.; Ruchon, T.; Soifer, H.; Staedter, D.; Wilkinson, I.; Stolow, A.; Dudovich, N.; Mairesse, Y.
2015-01-01
High-order harmonic generation in polyatomic molecules generally involves multiple channels of ionization. Their relative contribution can be strongly influenced by the presence of resonances, whose assignment remains a major challenge for high-harmonic spectroscopy. Here we present a multi-modal approach for the investigation of unaligned polyatomic molecules, using SF6 as an example. We combine methods from extreme-ultraviolet spectroscopy, above-threshold ionization and attosecond metrology. Fragment-resolved above-threshold ionization measurements reveal that strong-field ionization opens at least three channels. A shape resonance in one of them is found to dominate the signal in the 20–26 eV range. This resonance induces a phase jump in the harmonic emission, a switch in the polarization state and different dynamical responses to molecular vibrations. This study demonstrates a method for extending high-harmonic spectroscopy to polyatomic molecules, where complex attosecond dynamics are expected. PMID:25608712
Ferr, A; Boguslavskiy, A E; Dagan, M; Blanchet, V; Bruner, B D; Burgy, F; Camper, A; Descamps, D; Fabre, B; Fedorov, N; Gaudin, J; Geoffroy, G; Mikosch, J; Patchkovskii, S; Petit, S; Ruchon, T; Soifer, H; Staedter, D; Wilkinson, I; Stolow, A; Dudovich, N; Mairesse, Y
2015-01-01
High-order harmonic generation in polyatomic molecules generally involves multiple channels of ionization. Their relative contribution can be strongly influenced by the presence of resonances, whose assignment remains a major challenge for high-harmonic spectroscopy. Here we present a multi-modal approach for the investigation of unaligned polyatomic molecules, using SF6 as an example. We combine methods from extreme-ultraviolet spectroscopy, above-threshold ionization and attosecond metrology. Fragment-resolved above-threshold ionization measurements reveal that strong-field ionization opens at least three channels. A shape resonance in one of them is found to dominate the signal in the 20-26?eV range. This resonance induces a phase jump in the harmonic emission, a switch in the polarization state and different dynamical responses to molecular vibrations. This study demonstrates a method for extending high-harmonic spectroscopy to polyatomic molecules, where complex attosecond dynamics are expected. PMID:25608712
Efficient calculation of anharmonic vibrational spectra of large molecules with localized modes.
Panek, Pawe? T; Jacob, Christoph R
2014-10-20
The analysis and interpretation of the vibrational spectra of complex (bio)molecular systems, such as polypeptides and proteins, requires support from quantum-chemical calculations. Such calculations are currently restricted to the harmonic approximation. Here, we show how one of the main bottlenecks in such calculations, the evaluation of the potential energy surface, can be overcome by using localized modes instead of the commonly employed normal modes. We apply such local vibrational self-consistent field (L-VSCF) and vibrational configuration interaction (L-VCI) calculations to a cyclic water tetramer and a helical hexa-alanine peptide. The results show that the use of localized modes is equivalent to the commonly used normal modes, but offers several advantages. First, a faster convergence with respect to the excitation level is observed in L-VCI calculations. Second, the localized modes provide a reduced representation of the couplings between modes that show a regular coupling pattern. This can be used to disregard a significant number of small two-mode potentials a priori. Several such reduced coupling approximations are explored, and we show that the number of single-point calculations required to evaluate the potential energy surface can be significantly reduced without introducing noticeable errors in the resulting vibrational spectra. PMID:25080397
Higher harmonic control analysis for vibration reduction of helicopter rotor systems
NASA Technical Reports Server (NTRS)
Nguyen, Khanh Q.
1994-01-01
An advanced higher harmonic control (HHC) analysis has been developed and applied to investigate its effect on vibration reduction levels, blade and control system fatigue loads, rotor performance, and power requirements of servo-actuators. The analysis is based on a finite element method in space and time. A nonlinear time domain unsteady aerodynamic model, based on the indicial response formulation, is used to calculate the airloads. The rotor induced inflow is computed using a free wake model. The vehicle trim controls and blade steady responses are solved as one coupled solution using a modified Newton method. A linear frequency-domain quasi-steady transfer matrix is used to relate the harmonics of the vibratory hub loads to the harmonics of the HHC inputs. Optimal HHC is calculated from the minimization of the vibratory hub loads expressed in term of a quadratic performance index. Predicted vibratory hub shears are correlated with wind tunnel data. The fixed-gain HHC controller suppresses completely the vibratory hub shears for most of steady or quasi-steady flight conditions. HHC actuator amplitudes and power increase significantly at high forward speeds (above 100 knots). Due to the applied HHC, the blade torsional stresses and control loads are increased substantially. For flight conditions where the blades are stalled considerably, the HHC input-output model is quite nonlinear. For such cases, the adaptive-gain controller is effective in suppressing vibratory hub loads, even though HHC may actually increase stall areas on the rotor disk. The fixed-gain controller performs poorly for such flight conditions. Comparison study of different rotor systems indicates that a soft-inplane hingeless rotor requires less actuator power at high speeds (above 130 knots) than an articulated rotor, and a stiff-inplane hingeless rotor generally requires more actuator power than an articulated or a soft-inplane hingeless rotor. Parametric studies for a hingeless rotor operating in a transition flight regime and for an articulated rotor operating at the level-flight boundary (high speed and high thrust conditions) indicate that blade parameters including flap, lag, torsion stiffness distributions, linear pretwist, chordwise offset of center-of-mass from elastic axis and chordwise offset of elastic axis from aerodynamic center can be selected to minimize the actuator power requirements for HHC.
NASA Technical Reports Server (NTRS)
Chiang, C. K.; Xue, David Y.; Mei, Chuh
1993-01-01
A finite element formulation is presented for determining the large-amplitude free and steady-state forced vibration response of arbitrarily laminated anisotropic composite thin plates using the Discrete Kirchhoff Theory (DKT) triangular elements. The nonlinear stiffness and harmonic force matrices of an arbitrarily laminated composite triangular plate element are developed for nonlinear free and forced vibration analyses. The linearized updated-mode method with nonlinear time function approximation is employed for the solution of the system nonlinear eigenvalue equations. The amplitude-frequency relations for convergence with gridwork refinement, triangular plates, different boundary conditions, lamination angles, number of plies, and uniform versus concentrated loads are presented.
NASA Astrophysics Data System (ADS)
Wang, Y. Q.; Guo, X. H.; Li, Y. G.; Li, J.
2010-03-01
This is a study of nonlinear traveling wave response of a cantilever circular cylindrical shell subjected to a concentrated harmonic force moving in a concentric circular path at a constant velocity. Donnell's shallow-shell theory is used, so that moderately large vibrations are analyzed. The problem is reduced to a system of ordinary differential equations by means of the Galerkin method. Frequency-responses for six different mode expansions are studied and compared with that for single mode to find the more contracted and accurate mode expansion investigating traveling wave vibration. The method of harmonic balance is applied to study the nonlinear dynamic response in forced oscillations of this system. Results obtained with analytical method are compared with numerical simulation, and the agreement between them bespeaks the validity of the method developed in this paper. The stability of the period solutions is also examined in detail.
Calculation of unsteady linearized Euler flows in cascades using harmonically deforming grids
NASA Technical Reports Server (NTRS)
Hall, Kenneth C.; Clark, William S.
1991-01-01
A method for calculating unsteady, inviscid, compressible flows in cascades is presented. Using the linearized Euler technique, the flow is decomposed into a steady or mean flow plus a harmonically varying small disturbance flow. The equations that describe the small disturbance flow are linear variable coefficient equations, and are solved using a pseudo-time time marching Lax-Wendroff technique. Unlike previous linearized methods, however, the solution is computed on a harmonically deforming computational grid that conforms to the motion of the vibrating airfoils. The mean flow and perturbation flow solutions are defined in the deforming coordinate system rather than in a coordinate system fixed in space. Hence, no extrapolation terms are required to implement the upwash boundary conditions at the airfoil surfaces, significantly improving the accuracy of the method. For transonic flow calculations, unsteady shock motions are modelled using shock capturing. The unsteady loads due to the shock motion are then seen as pressure impulses. Representative computational results are presented for transonic channel flows and subsonic and transonic cascade flows.
Harmonic two-phonon {gamma}-vibrational state in neutron-rich {sup 106}Mo
Guessous, A.; Schulz, N.; Phillips, W.R.; Ahmad, I.; Bentaleb, M.; Durell, J.L.; Jones, M.A.; Leddy, M.; Lubkiewicz, E.; Morss, L.R.; Piepenbring, R.; Smith, A.G.; Urban, W.; Varley, B.J.
1995-09-18
The neutron-rich {sup 106}Mo nucleus has been studied by prompt {gamma}-ray spectroscopy following the spontaneous fission of {sup 248}Cm. The characteristics of the rotational band built on a state at 1435 keV identifies the band head as the best candidate for a harmonic double-phonon {ital K}{sup {pi}}=4{sup +} {gamma}-vibrational state observed so far.
NASA Astrophysics Data System (ADS)
Ayyappan, S.; Sundaraganesan, N.; Aroulmoji, V.; Murano, E.; Sebastian, S.
2010-09-01
The FT-IR and FT-Raman spectral studies of the Methotrexate (MTX) were carried out. The equilibrium geometry, various bonding features and harmonic vibrational frequencies of MTX have been investigated with the help of B3LYP density functional theory (DFT) using 6-31G(d) as basis set. Detailed analysis of the vibrational spectra has been made with the aid of theoretically predicted vibrational frequencies. The vibrational analysis confirms the differently acting ring modes, steric repulsion, conjugation and back-donation. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complement with the experimental findings. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. Good correlations between the experimental 1H and 13C NMR chemical shifts in DMSO solution and calculated GIAO shielding tensors were found.
Ab initio and DFT calculations of the structure and vibrational spectra of trigonelline
NASA Astrophysics Data System (ADS)
Szafran, M.; Koput, J.; Dega-Szafran, Z.; Pankowski, M.
2002-09-01
The geometries, frequencies and infrared intensities of the vibrational bands of trigonelline its monohydrate and dimer have been computed by the MP2 and B3LYP approaches using the cc-pVDZ and 6-31G(d,p) basis sets. The computed geometry of the pyridine ring is slightly affected by hydration and dimerization, and satisfactorily agrees with the X-ray data. In contrast, the geometry of the COO group changes significantly on hydration and dimerization. All the measured IR bands were assigned in terms of the calculated vibrational modes. Most computed bands are predicted to lie at higher wavenumbers than the experimental bands. R.M.S. deviation between the experimental and the calculated harmonic frequencies is 69 cm -1 for all of the bands, and 46 cm -1 for all bands except those corresponding to ?(OH), ?(OH) and ?(CH).
Investigation of the vibration of a blade with friction damper by HBM. [Harmonic Balance Method
Wang, J.H.; Chen, W.K. )
1993-04-01
The friction damper has been widely used to reduce the resonant vibration of blades. The most commonly used methods for studying the dynamic behavior of a blade with a friction damper are direct integration methods. Although the harmonic balance method (HBM) is a well-known method for studying nonlinear vibration problems, generally only a one-term approximation has been proposed to study the nonlinear vibration of a frictionally damped blade. In this work, a HMB procedure with a multiterm approximation is proposed. The results show that the steady-state response and other related behavior of a frictionally damped blade can be predicted accurately and quickly by an HBM with a multiterm approximation.
A vibrational spectroscopy study on 3-aminophenylacetic acid by DFT calculations
NASA Astrophysics Data System (ADS)
Akkaya, Yasemin; Balci, Kubilay; Goren, Yeliz; Akyuz, Sevim
2015-08-01
In this study, in which the group vibrations of 3-aminophenylacetic acid were investigated by electronic structure calculations based on Density Functional Theory (DFT), the possible stable conformers of the molecule were searched through a relaxed "potential energy surface scan" carried out at B3LYP/6-31G(d) level of theory. The corresponding equilibrium geometrical and vibrational spectral data for each of the determined stable conformers and for their possible dimer structures were obtained through "geometry optimisation" and "frequency" calculations carried out at B3LYP/6-31G(d) and B3LYP/6-311G++(d,p) levels of theory. The obtained results confirmed that anharmonic wavenumbers calculated at B3LYP/6-311G++(d,p) level generally quite well agree with the experimental wavenumbers, however, harmonic wavenumbers calculated at both levels of theory need an efficient refinement for a satisfactory agreement with experiment. In particular, the harmonic wavenumbers, IR and Raman intensities refined within Scaled Quantum Mechanical Force Field (SQM FF) methodology constituted the primary data set in the interpretation of the experimental FT-IR, FT-Raman and dispersive Raman spectra of 3-aminophenylacetic acid. By the help of these refined spectral data, the effects of conformation and intermolecular hydrogen bonding on the fundamental bands observed in the experimental spectra could be correctly predicted.
A vibrational spectroscopy study on 3-aminophenylacetic acid by DFT calculations.
Akkaya, Yasemin; Balci, Kubilay; Goren, Yeliz; Akyuz, Sevim
2015-08-01
In this study, in which the group vibrations of 3-aminophenylacetic acid were investigated by electronic structure calculations based on Density Functional Theory (DFT), the possible stable conformers of the molecule were searched through a relaxed "potential energy surface scan" carried out at B3LYP/6-31G(d) level of theory. The corresponding equilibrium geometrical and vibrational spectral data for each of the determined stable conformers and for their possible dimer structures were obtained through "geometry optimisation" and "frequency" calculations carried out at B3LYP/6-31G(d) and B3LYP/6-311G++(d,p) levels of theory. The obtained results confirmed that anharmonic wavenumbers calculated at B3LYP/6-311G++(d,p) level generally quite well agree with the experimental wavenumbers, however, harmonic wavenumbers calculated at both levels of theory need an efficient refinement for a satisfactory agreement with experiment. In particular, the harmonic wavenumbers, IR and Raman intensities refined within Scaled Quantum Mechanical Force Field (SQM FF) methodology constituted the primary data set in the interpretation of the experimental FT-IR, FT-Raman and dispersive Raman spectra of 3-aminophenylacetic acid. By the help of these refined spectral data, the effects of conformation and intermolecular hydrogen bonding on the fundamental bands observed in the experimental spectra could be correctly predicted. PMID:25854610
NASA Astrophysics Data System (ADS)
Gao, Hongwei; Xia, FengYi; Huang, ChangJiang; Lin, Kuangfei
2011-04-01
A comparison of six density functional theory (DFT) methods and six basis sets for predicting the molecular structures and vibration spectra of cisplatin is reported. The theoretical results are discussed and compared with the experimental data. It is remarkable that LSDA/SDD level is clearly superior to all the remaining density functional methods (including mPW1PW) in predicting the structures of cisplatin. Mean deviation between the calculated harmonic and observed fundamental vibration frequencies for each method is also calculated. The results indicate that PBE1PBE/SDD is the best method to predict all frequencies on average for cisplatin molecule in DFT methods.
Fully automated microcomputer calculation of vibrational spectra
NASA Astrophysics Data System (ADS)
Dowty, Eric
1987-01-01
A fully automated method for computing frequencies and atomic displacements of normal modes, giving synthetic infrared and Raman spectra, has been developed for use on small computers. No expertise in group theory or the mathematics of normal-mode calculation are required to use the computer program. The method takes full account of symmetry and is applicable to any crystal or molecule. Force constants can be specified in terms of any two-atom bonds or three-atom angles. The essential steps in the computer program are: (1) Locate all atoms in the unit cell or molecule and compute displacement vectors for each internal coordinate; (2) Convert the basis of the force constants from bonds and angles to cartesian displacements; (3) Construct the full-matrix irreducible representations of the point or factor group in question, using appropriate symmetry matrices and polynomial basis functions; (4) Derive the symmetry coordinates in terms of cartesian displacements using the projection/transfer-operator technique; (5) construct secular equations for each species with Wilson's f g method; (6) solve for frequencies and atomic motions; and (7) use simple models of infrared and Raman intensities to calculate spectra.
Chen, Jun; Zhu, Guang; Yang, Weiqing; Jing, Qingshen; Bai, Peng; Yang, Ya; Hou, Te-Chien; Wang, Zhong Lin
2013-11-13
A harmonic-resonator-based triboelectric nanogenerator (TENG) is presented as a sustainable power source and an active vibration sensor. It can effectively respond to vibration frequencies ranging from 2 to 200 Hz with a considerably wide working bandwidth of 13.4 Hz. This work not only presents a new principle in the field of vibration energy harvesting but also greatly expands the applicability of TENGs. PMID:23999798
Vibronic-structure tracking: A shortcut for vibrationally resolved UV/Vis-spectra calculations
Barton, Dennis; König, Carolin; Neugebauer, Johannes
2014-10-28
The vibrational coarse structure and the band shapes of electronic absorption spectra are often dominated by just a few molecular vibrations. By contrast, the simulation of the vibronic structure even in the simplest theoretical models usually requires the calculation of the entire set of normal modes of vibration. Here, we exploit the idea of the mode-tracking protocol [M. Reiher and J. Neugebauer, J. Chem. Phys. 118, 1634 (2003)] in order to directly target and selectively calculate those normal modes which have the largest effect on the vibronic band shape for a certain electronic excitation. This is achieved by defining a criterion for the importance of a normal mode to the vibrational progressions in the absorption band within the so-called “independent mode, displaced harmonic oscillator” (IMDHO) model. We use this approach for a vibronic-structure investigation for several small test molecules as well as for a comparison of the vibronic absorption spectra of a truncated chlorophyll a model and the full chlorophyll a molecule. We show that the method allows to go beyond the often-used strategy to simulate absorption spectra based on broadened vertical excitation peaks with just a minimum of computational effort, which in case of chlorophyll a corresponds to about 10% of the cost for a full simulation within the IMDHO approach.
Nonlinear coupled rotor-fuselage helicopter vibration studies with higher harmonic control
NASA Technical Reports Server (NTRS)
Friedmann, P. P.; Venkatesan, C.; Papavassiliou, I.
1990-01-01
This paper addresses the problem of vibration prediction and vibration reduction in helicopters by means of active control methodologies. The nonlinear equations of a coupled rotor/flexible-fuselage system have been derived using computer algebra, thus relegating this tedious task to the computer. In the solution procedure the trim state and vibratory response of the helicopter are obtained in a single pass by using a harmonic balance technique and simultaneously satisfying the trim and the vibratory response of the helicopter in all the rotor and fuselage degrees of freedom. Using this solution procedure, the influence of the fuselage flexibility on the vibratory response is studied. In addition, it is shown that the conventional single frequency HHC is capable of reducing either the hub loads or only the fuselage vibrations but not both simultaneously. A new scheme called MHHC, having multiple higher harmonic pitch inputs, was used to accomplish this task of simultaneously reducing both the vibratory hub loads and fuselage vibratory response. In addition, the uniqueness of this MHHC scheme is explained in detail.
NASA Astrophysics Data System (ADS)
Edwin, Bismi; Hubert Joe, I.
2012-11-01
Vibrational spectral analysis and quantum chemical computations based on density functional theory have been performed on the anti-neuro-degenerative drug Orphenadrine hydrochloride. The geometry, intermolecular hydrogen bond, and harmonic vibrational frequencies of the title molecule have been investigated with the help of B3LYP method. The calculated molecular geometry has been compared with the experimental data. The various intramolecular interactions have been exposed by natural bond orbital analysis. The distribution of Mulliken atomic charges and bending of natural hybrid orbitals also reflect the presence of intramolecular hydrogen bonding. The analysis of the electron density of HOMO and LUMO gives an idea of the delocalization and low value of energy gap indicates electron transport in the molecule and thereby bioactivity. Effective docking of the drug molecule with NMDA receptor subunit 3A also enhances its bioactive nature.
Diabatic Versus Adiabatic Calculation of Torsion-Vibration Interactions
NASA Astrophysics Data System (ADS)
Hougen, Jon T.
2013-06-01
The introductory part of this talk will deal briefly with two historical topics: (i) use of the words adiabatic, nonadiabatic, and diabatic in thermodynamics and quantum mechanics, and (ii) application of diabatic and adiabatic ideas to vibrational energy level calculations for a pair of diatomic-molecule potential energy curves exhibiting an avoided crossing. The main part of the talk will be devoted to recent work with Li-Hong Xu and Ron Lees on how ab initio projected frequency calculations for small-amplitude vibrations along the large-amplitude internal rotation path in methanol can best be used to help guide experimental assignments and fits in the IR vibrational spectrum. The three CH stretching vibrations for CH_{3}OH can conveniently be represented as coefficients multiplying three different types of basis vibrations, i.e., as coefficients of: (i) the local mode C-H_i bond displacements ?r_{i} for hydrogens H_{1}, H_{2} and H_{3} of the methyl top, (ii) symmetrized linear combinations of the three ?r_{i} of species A_{1} oplus E in the permutation-inversion group G_{6} = C_{3v} appropriate for methanol, or (iii) symmetrized linear combinations of the three ?r_{i} of species 2A_{1} oplus A_{2} in the permutation-inversion group G_{6}. In this talk, we will focus on diabatic and adiabatic computations for the A_{1} oplus E basis vibrations of case (ii) above. We will briefly explain how Jahn-Teller-like and Renner-Teller-like torsion-vibration interaction terms occurring in the potential energy expression in the diabatic calculation become torsion-vibration Coriolis interaction terms occurring in the kinetic energy expression of the adiabatic calculations, and also show how, for algebraically solvable parameter choices, the same energy levels are obtained from either calculation. A final conclusion as to which approach is computationally superior for the numerical data given in a quantum chemistry output file has not yet been arrived at.
Sarshar, A.; Iravani, M.R.; Li, J.
1996-01-01
In this paper, noncharacteristic harmonics of an HVdc converter station are calculated based on the use of digital time-domain simulation methods. An enhanced version of the Electromagnetic Transients Program (EMTP) is used for the studies. The noncharacteristic harmonics of interest are (1) the dc side triplen harmonics, and (2) the ac side second harmonic. Impacts of loading conditions, neutral filter, and converter firing angle on the dc side triplen harmonics are discussed. Effects of ac side network parameters, static VAR compensator (SVC), transformer half-cycle saturation, and Geomagnetically Induced Current (GIC) on the ac side second harmonic instability are also presented. This paper concludes that the digital time-domain simulation method provides significant flexibility for accurate prediction of (1) generation mechanism, and (2) adverse impacts of HVdc noncharacteristic harmonics.
A piezoelectric pulse generator for low frequency non-harmonic vibration
NASA Astrophysics Data System (ADS)
Jiang, Hao; Yeatman, Eric M.
2013-12-01
This paper reports a new piezoelectric prototype for pulse generation by energy harvesting from low frequency non-harmonic vibration. The pulse generator presented here consists of two parts: the electromechanical part and the load circuit. A metal rolling rod is used as the proof mass, moving along the substrate to achieve both actuating of the piezoelectric cantilever by magnetic coupling and self-synchronous switching of the circuit. By using this new approach, the energy from the piezoelectric transduction mechanism is regulated simultaneously when it is extracted. This allows a series of tuneable pulses to be generated, which can be applied to self-powered RF wireless sensor network (WSN) nodes.
Do, Hainam; Besley, Nicholas A
2015-02-01
Vibrational frequencies for carbon clusters, fullerenes and nanotubes evaluated using empirical carbon-carbon potentials are presented. For linear and cyclic clusters, frequencies evaluated with the reactive empirical bond order (REBO) potential provide the closest agreement with experiment. The mean absolute deviation (MAD) between experiment and the calculated harmonic frequencies is 79 cm(-1) for the bending modes and 76 cm(-1) for the stretching modes. The effects of anharmonicity are included via second order vibrational perturbation theory and tend to increase the frequency of the bending modes while the stretching modes have negative shifts in the region of 20-60 cm(-1), with larger shifts for the higher frequency modes. This results in MADs for the bending and stretching modes of 84 cm(-1) and 58 cm(-1), respectively. For the fullerene molecule C60, the high frequency modes are predicted to have harmonic frequencies that are significantly higher than experiment, and this is not corrected by accounting for anharmonicity. This overestimation of experimental observed frequencies is also evident in the calculated frequencies of the G band in nanotubes. This suggests that the REBO potential is not optimal for these larger systems and it is shown that adjustment of the parameters within the potential leads to closer agreement with experiment, particularly if higher and lower frequency modes are considered separately. PMID:25559973
NASA Astrophysics Data System (ADS)
Gao, Hongwei; Wei, Xiujuan; Liu, Xuting; Huang, Changjiang
2010-10-01
The molecular structure and vibrational frequencies of cis-[Pt(CH 3CN) 2Cl 2] were calculated by five density functional theory (DFT) and HF methods using several basis sets. The theoretical results are discussed and compared with the experimental data. It is remarkable that mPW1PW91 and PBE1PBE methods at SDD basis sets are clearly superior to the remaining density functional methods in predicting the structures of cis-[Pt(CH 3CN) 2Cl 2]. Mean deviation between the calculated harmonic and observed fundamental vibrational frequencies for each method is also calculated. The results indicate that mPW1PW91 and PBE1PBE methods at SDD basis sets are also the best to predict vibrational spectra of cis-[Pt(CH 3CN) 2Cl 2].
Harmonic resonance structure and chaotic dynamics in the earth-vibrator system
Walker, D.
1995-05-01
Source-generated energy in seismic vibrator records includes ultraharmonics, sub-harmonics, ultra-subharmonics and possibly chaotic oscillatory behavior. Non-linear behaviors can be modeled using a ``hard-spring`` form of the Duffing equation. Modeling indicates that a qualitatively similar harmonic resonance structure is present for a broad range of possible mathematical descriptions. Qualitative global system behaviors may be examined without knowledge of actual earth parameters. Non-linear resonances become stronger, relative to fundamental sweep frequencies, as the driving force increases or damping decreases. System response energy levels are highest when non-linear resonances are strong. The presence of chaotic energy can indicate the highest energy state of a system response. Field data examples are consistent with behaviors predicted by modeling. Conventional correlation and stack uses a fraction of the energy produced in the earth-vibrator system. A correlation and filtering process that uses a representation of the source dynamics based on the system response can reduce signal degradation due to non-linear resonance.
On the effect of acoustic coupling on random and harmonic plate vibrations
NASA Technical Reports Server (NTRS)
Frendi, A.; Robinson, J. H.
1993-01-01
The effect of acoustic coupling on random and harmonic plate vibrations is studied using two numerical models. In the coupled model, the plate response is obtained by integration of the nonlinear plate equation coupled with the nonlinear Euler equations for the surrounding acoustic fluid. In the uncoupled model, the nonlinear plate equation with an equivalent linear viscous damping term is integrated to obtain the response of the plate subject to the same excitation field. For a low-level, narrow-band excitation, the two models predict the same plate response spectra. As the excitation level is increased, the response power spectrum predicted by the uncoupled model becomes broader and more shifted towards the high frequencies than that obtained by the coupled model. In addition, the difference in response between the coupled and uncoupled models at high frequencies becomes larger. When a high intensity harmonic excitation is used, causing a nonlinear plate response, both models predict the same frequency content of the response. However, the level of the harmonics and subharmonics are higher for the uncoupled model. Comparisons to earlier experimental and numerical results show that acoustic coupling has a significant effect on the plate response at high excitation levels. Its absence in previous models may explain the discrepancy between predicted and measured responses.
Vibrational spectra and DFT calculations of sonderianin diterpene
NASA Astrophysics Data System (ADS)
Oliveira, I. M. M.; Santos, H. S.; Sena, D. M.; Cruz, B. G.; Teixeira, A. M. R.; Freire, P. T. C.; Braz-Filho, R.; Sousa, J. W.; Albuquerque, M. R. J. R.; Bandeira, P. N.; Bernardino, A. C. S. S.; Gusmo, G. O. M.; Bento, R. R. F.
2015-11-01
In the present study, the natural product sonderianin diterpene (C21H26O4), a diterpenoid isolated from Croton blanchetianus, with potential application in the drug industry, was characterized by nuclear magnetic resonance, infrared and Raman spectroscopy. Vibrational spectra were supported by Density Functional Theory calculations. Infrared and Raman spectra of sonderianin were recorded at ambient temperature in the regions from 400cm-1 to 3600cm-1 and from 40cm-1 to 3500cm-1, respectively. DFT calculations with the hybrid functional B3LYP and the basis set 6-31G(d,p) were performed with the purpose of obtaining information on the structural and vibrational properties of this organic compound. A comparison with experimental spectra allowed us to assign all of the normal modes of the crystal. The assignment of the normal modes was carried out by means of potential energy distribution.
Molecular structure and vibrational spectra of ibuprofen using density function theory calculations
NASA Astrophysics Data System (ADS)
Liu, Lekun; Gao, Hongwei
2012-04-01
The molecular geometry and the theoretical harmonic frequencies and infrared intensities of ibuprofen were calculated for all the molecules using five different density functional methods (mPW1PW91, B3PW91, B3LYP, HCTH and LSDA) with five basic sets, including 6-311G, 6-311++G, 6-311+G (d, p), 6-311++G (d, p) and 6-311++G (2d, 2p). The purpose of this research was to compare the performance of different DFT methods at different basis sets in predicting geometry and vibration spectrum of ibuprofen. The optimized geometric band lengths and bond angles obtained by using mPW1PW91 at 6-311++G (d, p) and 6-311++G (2d, 2p) basic sets show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of ibuprofen with calculated results indicates that the B3PW91/6-311++G (2d, 2p) level is superior to all the remaining levels for predicting all the vibration spectra on average for ibuprofen.
Calculation of ground vibration spectra from heavy military vehicles
NASA Astrophysics Data System (ADS)
Krylov, V. V.; Pickup, S.; McNuff, J.
2010-07-01
The demand for reliable autonomous systems capable to detect and identify heavy military vehicles becomes an important issue for UN peacekeeping forces in the current delicate political climate. A promising method of detection and identification is the one using the information extracted from ground vibration spectra generated by heavy military vehicles, often termed as their seismic signatures. This paper presents the results of the theoretical investigation of ground vibration spectra generated by heavy military vehicles, such as tanks and armed personnel carriers. A simple quarter car model is considered to identify the resulting dynamic forces applied from a vehicle to the ground. Then the obtained analytical expressions for vehicle dynamic forces are used for calculations of generated ground vibrations, predominantly Rayleigh surface waves, using Green's function method. A comparison of the obtained theoretical results with the published experimental data shows that analytical techniques based on the simplified quarter car vehicle model are capable of producing ground vibration spectra of heavy military vehicles that reproduce basic properties of experimental spectra.
Vibrational and structural study of onopordopicrin based on the FTIR spectrum and DFT calculations.
Chain, Fernando E; Romano, Elida; Leyton, Patricio; Paipa, Carolina; Cataln, Csar A N; Fortuna, Mario; Brandn, Silvia Antonia
2015-11-01
In the present work, the structural and vibrational properties of the sesquiterpene lactone onopordopicrin (OP) were studied by using infrared spectroscopy and density functional theory (DFT) calculations together with the 6-31G(?) basis set. The harmonic vibrational wavenumbers for the optimized geometry were calculated at the same level of theory. The complete assignment of the observed bands in the infrared spectrum was performed by combining the DFT calculations with Pulay's scaled quantum mechanical force field (SQMFF) methodology. The comparison between the theoretical and experimental infrared spectrum demonstrated good agreement. Then, the results were used to predict the Raman spectrum. Additionally, the structural properties of OP, such as atomic charges, bond orders, molecular electrostatic potentials, characteristics of electronic delocalization and topological properties of the electronic charge density were evaluated by natural bond orbital (NBO), atoms in molecules (AIM) and frontier orbitals studies. The calculated energy band gap and the chemical potential (?), electronegativity (?), global hardness (?), global softness (S) and global electrophilicity index (?) descriptors predicted for OP low reactivity, higher stability and lower electrophilicity index as compared with the sesquiterpene lactone cnicin containing similar rings. PMID:26057092
NASA Astrophysics Data System (ADS)
Balci, K.; Akyuz, S.
2005-06-01
A detailed investigation of the geometric structure, force field, electro-optical parameters, relative IR intensities and harmonic vibrational wavenumbers of free 4-aminopyrimidine molecule (4APM) in the electronically ground state has been carried out by using both the DFT-B3LYP (with 6-31++G(d,p) double and 6-311++G(d,p) triple basis sets) and force field refinement calculation methods. The vibrational wavenumbers calculated with DFT method were scaled by using two different methods: (1) scaling with dual scaling factors, (2) deriving the scaling factors from the graph of observed versus calculated wavenumbers. In the case of force field refinement method, the force constants of the pyrimidine were slightly refined so as to fit the calculated wavenumbers to the experimental ones. In order to define the contributions of the internal coordinates of the molecule on its each normal vibrational mode, P.E.D. calculations were performed. In wavenumber and PED calculations, both methods have yield results in agreement with the experimental assignment and also with each other, particularly for ring vibrations. The relative IR intensities calculated by the force field refinement method are considerably in good agreement with experimental ones, however, the results of the IR intensities, obtained from the DFT method are found to be significantly different from the experimental values.
An improved filtered spherical harmonic method for transport calculations
Ahrens, C.; Merton, S.
2013-07-01
Motivated by the work of R. G. McClarren, C. D. Hauck, and R. B. Lowrie on a filtered spherical harmonic method, we present a new filter for such numerical approximations to the multi-dimensional transport equation. In several test problems, we demonstrate that the new filter produces results with significantly less Gibbs phenomena than the filter used by McClarren, Hauck and Lowrie. This reduction in Gibbs phenomena translates into propagation speeds that more closely match the correct propagation speed and solutions that have fewer regions where the scalar flux is negative. (authors)
NASA Astrophysics Data System (ADS)
Pfeiffer, Florian; Rauhut, Guntram; Feller, David; Peterson, Kirk A.
2013-01-01
Anharmonic zero point vibrational energies (ZPVEs) calculated using both conventional CCSD(T) and MP2 in combination with vibrational second-order perturbation theory (VPT2) are compared to explicitly correlated CCSD(T)-F12 and MP2-F12 results that utilize vibrational configuration interaction (VCI) theory for 26 molecules of varying size. Sequences of correlation consistent basis sets are used throughout. It is found that the explicitly correlated methods yield results close to the basis set limit even with double-zeta quality basis sets. In particular, the anharmonic contributions to the ZPVE are accurately recovered at just the MP2 (or MP2-F12) level of theory. Somewhat surprisingly, the best vibrational CI results agreed with the VPT2 values with a mean unsigned deviation of just 0.09 kJ/mol and a standard deviation of just 0.11 kJ/mol. The largest difference was observed for C4H4O (0.34 kJ/mol). A simplified version of the vibrational CI procedure that limited the modal expansion to at most 2-mode coupling yielded anharmonic corrections generally within about 0.1 kJ/mol of the full 3- or 4-mode results, except in the cases of C3H8 and C4H4O where the contributions were underestimated by 1.3 and 0.8 kJ/mol, respectively (34% and 40%, respectively). For the molecules considered in this work, accurate anharmonic ZPVEs are most economically obtained by combining CCSD(T)-F12a/cc-pVDZ-F12 harmonic frequencies with either MP2/aug-cc-pVTZ/VPT2 or MP2-F12/cc-pVDZ-F12/VCI anharmonic corrections.
Calculation of the vibrational spectra of betaine hydrochloride
NASA Astrophysics Data System (ADS)
Szafran, Miroslaw; Koput, Jacek
1997-02-01
The molecular geometries of betaine hydrochloride, BETHCl, and free protonated betaine, BETH +, were calculated with the 6-31G(d,p) basis set at the SCF, MP2 and DFT levels of theory. At the SCF level, the minimum energy corresponds to the ionic pair, B +Htctdot;A -, however, the equilibrium Otctdot;Cl distance is 0.14 shorter than the X-ray value. Inclusion of the correlation effects, both at the MP2 and DFT levels, predicts a minimum energy for the molecular complex, Btctdot;H-A, with the equilibrium Otctdot;Cl distance close to the experimental value. The frequencies and intensities of the vibrational bands of BETHCl, BETDCl and BETH + were calculated at the SCF and DFT levels and compared with the solid IR spectra. All measured IR bands were interpreted in term of the calculated vibrational modes. The rms deviations between the experimental and calculated SCF frequencies were 21 and 29 cm -1 for BETHCl and BETDCl, respectively. The computed band intensities agree qualitatively with the experimental data. The coupling of the CO stretching and OH bending modes are discussed. The summation bands are probably enhanced in intensity by Fermi resonance with the fundamentals responsible for the main ?(OH) (?(OD) absorption region.
NASA Astrophysics Data System (ADS)
Howard, J. Coleman; Enyard, Jordan D.; Tschumper, Gregory S.
2015-12-01
A wide range of density functional theory (DFT) methods (37 altogether), including pure, hybrid, range-separated hybrid, double-hybrid, and dispersion-corrected functionals, have been employed to compute the harmonic vibrational frequencies of eight small water clusters ranging in size from the dimer to four different isomers of the hexamer. These computed harmonic frequencies have been carefully compared to recently published benchmark values that are expected to be very close to the CCSD(T) complete basis set limit. Of the DFT methods examined here, ?B97 and ?B97X are the most consistently accurate, deviating from the reference values by less than 20 cm-1 on average and never more than 60 cm-1. The performance of double-hybrid methods including B2PLYP and mPW2-PLYP is only slightly better than more economical approaches, such as the M06-L pure functional and the M06-2X hybrid functional. Additionally, dispersion corrections offer very little improvement in computed frequencies.
NASA Technical Reports Server (NTRS)
Papavassiliou, I.; Venkatesan, C.; Friedmann, P. P.
1990-01-01
A fundamental study of vibration prediction and vibration reduction in helicopters using active controls was performed. The nonlinear equations of motion for a coupled rotor/flexible fuselage system have been derived using computer algebra on a special purpose symbolic computing facility. The details of the derivation using the MACSYMA program are described. The trim state and vibratory response of the helicopter are obtained in a single pass by applying the harmonic balance technique and simultaneously satisfying the trim and the vibratory response of the helicopter for all rotor and fuselage degrees of freedom. The influence of the fuselage flexibility on the vibratory response is studied. It is shown that the conventional single frequency higher harmonic control (HHC) capable of reducing either the hub loads or only the fuselage vibrations but not both simultaneously. It is demonstrated that for simultaneous reduction of hub shears and fuselage vibrations a new scheme called multiple higher harmonic control (MHHC) is required. The fundamental aspects of this scheme and its uniqueness are described in detail, providing new insight on vibration reduction in helicopters using HHC.
Laury, Marie L; Boesch, Scott E; Haken, Ian; Sinha, Pankaj; Wheeler, Ralph A; Wilson, Angela K
2011-08-01
Scale factors for (a) low (<1000 cm(-1)) and high harmonic vibrational frequencies, (b) thermal contributions to enthalpy and entropy, and (c) zero-point vibrational energies have been determined for five hybrid functionals (B3P86, B3PW91, PBE1PBE, BH&HLYP, MPW1K), five pure functionals (BLYP, BPW91, PBEPBE, HCTH93, and BP86), four hybrid meta functionals (M05, M05-2X, M06, and M06-2X) and one double-hybrid functional (B2GP-PLYP) in combination with the correlation consistent basis sets [cc-pVnZ and aug-cc-pVnZ, n = D(2),T(3),Q(4)]. Calculations for vibrational frequencies were carried out on 41 organic molecules and an additional set of 22 small molecules was used for the zero-point vibrational energy scale factors. Before scaling, approximately 25% of the calculated frequencies were within 3% of experimental frequencies. Upon application of the derived scale factors, nearly 90% of the calculated frequencies deviated less than 3% from the experimental frequencies for all of the functionals when the augmented correlation consistent basis sets were used. PMID:21598273
Vibrational spectroscopic studies and DFT calculations of 4-bromo-o-xylene
NASA Astrophysics Data System (ADS)
Arivazhagan, M.; Meenakshi, R.
2012-06-01
In the present work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of 4-bromo-o-xylene (BOX). The FT-IR (400-4000 cm-1) and FT-Raman spectra (50-3500 cm-1) of BOX were recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of BOX in the ground state have been calculated by using the density functional B3LYP method with 6-311++G(d,p)/6-311+G(d,p) higher basis sets. The energy and oscillator strength are calculated by time-dependent density functional theory (TD-DFT). To determine conformational flexibility, molecular energy profile of BOX was obtained by B3LYP method with 6-311++G(d,p) basis set with respect to selected degree of torsional freedom, which gives three stable conformers. Besides, molecular electrostatic potential (MEP), non-linear properties and NMR analysis were performed at DFT level of theory.
Vibrational spectroscopic studies and DFT calculations of 4-bromo-o-xylene.
Arivazhagan, M; Meenakshi, R
2012-06-01
In the present work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of 4-bromo-o-xylene (BOX). The FT-IR (400-4000 cm(-1)) and FT-Raman spectra (50-3500 cm(-1)) of BOX were recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of BOX in the ground state have been calculated by using the density functional B3LYP method with 6-311++G(d,p)/6-311+G(d,p) higher basis sets. The energy and oscillator strength are calculated by time-dependent density functional theory (TD-DFT). To determine conformational flexibility, molecular energy profile of BOX was obtained by B3LYP method with 6-311++G(d,p) basis set with respect to selected degree of torsional freedom, which gives three stable conformers. Besides, molecular electrostatic potential (MEP), non-linear properties and NMR analysis were performed at DFT level of theory. PMID:22430759
NASA Astrophysics Data System (ADS)
Soobbarayen, K.; Besset, S.; Sinou, J.-. J.
2015-01-01
The acoustic response associated with squeal noise radiations is a hard issue due to the need to consider non-linearities of contact and friction, to solve the associated nonlinear dynamic problem and to calculate the noise emissions due to self-excited vibrations. In this work, the focus is on the calculation of the sound pressure in free space generated during squeal events. The calculation of the sound pressure can be performed by the Boundary Element Method (BEM). The inputs of this method are a boundary element model, a field of normal velocity characterized by a unique frequency. However, the field of velocity associated with friction-induced vibrations is composed of several harmonic components. So, the BEM equation has to be solved for each frequency and in most cases, the number of harmonic components is significant. Therefore, the computation time can be prohibitive. The reduction of the number of harmonic component is a key point for the quick estimation of the squeal noise. The proposed approach is based on the detection and the selection of the predominant harmonic components in the mean square velocity. It is applied on two cases of squeal and allows us to consider only few frequencies. In this study, a new method will be proposed in order to quickly well estimate the noise emission in free space. This approach will be based on an approximated acoustic power of brake system which is assumed to be a punctual source, an interpolated directivity and the decrease of the acoustic power levels. This method is applied on two classical cases of squeal with one and two unstable modes. It allows us to well reconstruct the acoustic power levels map. Several error estimators are introduced and show that the reconstructed field is close to the reference calculated with a complete BEM.
NASA Astrophysics Data System (ADS)
Hansen, Mikkel Bo; Christiansen, Ove; Httig, Christof
2009-10-01
Quadratic response functions are derived and implemented for a vibrational configuration interaction state. Combined electronic and vibrational quadratic response functions are derived using Born-Oppenheimer vibronic product wave functions. Computational tractable expressions are derived for determining the total quadratic response contribution as a sum of contributions involving both electronic and vibrational linear and quadratic response functions. In the general frequency-dependent case this includes a new and more troublesome type of electronic linear response function. Pilot calculations for the FH, H2O, CH2O, and pyrrole molecules demonstrate the importance of vibrational contributions for accurate comparison to experiment and that the vibrational contributions in some cases can be very large. The calculation of transition properties between vibrational states is combined with sum-over-states expressions for analysis purposes. On the basis of this some simple analysis methods are suggested. Also, a preliminary study of the effect of finite lifetimes on quadratic response functions is presented.
Large vibrational effects upon calculated phase boundaries in Al-Sc.
Ozoliņs, V; Asta, M
2001-01-15
The fcc portion of the Al-Sc phase diagram is calculated from first principles including contributions to alloy free energies associated with ionic vibrations. It is found that vibrational entropy accounts for a 27-fold increase in the calculated solubility limits for Sc in fcc Al at high temperatures, bringing calculated and measured values into very good agreement. The present work gives a clear example demonstrating a large effect of vibrational entropy upon calculated phase boundaries in substitutional alloys. PMID:11177852
Darkhalil, Ikhlas D; Paquet, Charles; Waqas, Mohammad; Gounev, Todor K; Durig, James R
2015-02-01
Variable temperature (-60 to -100 C) studies of ethyldichlorophosphine, CH3CH2PCl2, of the infrared spectra (4000-400 cm(-1)) dissolved in liquid xenon have been carried out. From these data, the two conformers have been identified and the enthalpy difference has been determined between the more stable trans conformer and the less stable gauche form to be 889 cm(-1) (1.040.11 kJ/mol). The percentage of abundance of the gauche conformer is estimated to be 57% at ambient temperature. The conformational stabilities have been predicted from ab initio calculations by utilizing many different basis sets up to aug-cc-pVTZ for both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been provided for both conformers which have been predicted by MP2(full)/6-31G(d) ab initio calculations to predict harmonic force fields, wavenumbers of the fundamentals, infrared intensities, Raman activities and depolarization ratios for both conformers. Estimated r0 structural parameters have been obtained from adjusted MP2(full)/6-311+G(d,p) calculations. The results are discussed and compared to the corresponding properties of some related molecules. PMID:24618201
NASA Astrophysics Data System (ADS)
Sangeetha, V.; Govindarajan, M.; Kanagathara, N.; Gunasekaran, S.; Rajakumar, P. R.; Anbalagan, G.
2014-06-01
Single crystals of melaminium bis (hydrogen oxalate) (MOX) were grown by slow evaporation method. X-ray powder diffraction analysis indicates that MOX crystallizes in monoclinic system (space group C2/c) and the calculated lattice constants are a = 20.075 0.123 ?, b = 8.477 0.045 ?, c = 6.983 0.015, ? = ? 90 and ? = 102.6 0.33. Thermal analysis confirms that MOX is thermally stable up to 250 C. A detailed interpretation of the FT-IR, FT-Raman and NMR spectra were reported. The equilibrium geometry, bonding features, and harmonic vibrational frequencies have been investigated with the help of PM6, HF and DFT/B3LYP methods. The potential energy curve shows that MOX molecule has two stable structures and the computational results diagnose that Rot I is the most stable conformer. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge-Invariant Atomic Orbital (GIAO) method. Stability of the molecule, arising from hyperconjugative interactions and charge delocalization, has been analyzed using Natural Bond Orbital (NBO) analysis. The electronic properties, such as HOMO and LUMO energies, were calculated by Time-Dependent DFT (TD-DFT) approach. To estimate chemical reactivity of the molecule, the molecular electrostatic potential (MEP) surface map is calculated for the optimized geometry of the molecule.
Guirgis, Gamil A; Dukes, Horace W; Wyatt, Justin K; Nielsen, Claus J; Horn, Anne; Aleksa, Valdemaras; Klaeboe, Peter
2015-02-01
Raman spectra of 1,1-difluoro-1-silacyclohexane as a liquid, and as a solid at 78 K were recorded and depolarization data obtained. The infrared spectra of the vapour, liquid and amorphous and crystalline solids have been studied. In the low temperature IR and Raman spectra eight and three bands, respectively, were shifted a few cm(-1) when the sample crystallized. No bands vanished after crystallization in agreement with the assumption that only one conformer (chair) was present in all the states of aggregation. The compound exists in the stable chair conformation, whereas in the parent silacyclohexane a possible twist form should have more than 15 kJ mol(-1) higher energies than the chair, as derived from various calculations. The wavenumbers of the vibrational modes were calculated in the harmonic and anharmonic approximation employing B3LYP/cc-pVTZ calculations. The 27 A' and 21 A? fundamentals were assigned on the basis of the calculations, infrared vapour contours, Raman depolarization measurements and infrared and Raman band intensities. An average, relative deviation of 1.5% was found between the observed and the anharmonic wavenumbers for the 48 modes. PMID:24238936
Spectral Analysis of Vibrational Harmonic Motion by use of a Continuous-Wave CO2 Doppler Lidar
NASA Technical Reports Server (NTRS)
Jarzembski, Maurice A.; Srivastava, Vandana
1999-01-01
Vibrational motion of a harmonic oscillator was investigated using a focused continuous wave CO2 Doppler lidar at 9.1 microns wavelength. A continuum of frequencies along with many discrete, equally spaced, resonant frequency modes was observed. The frequency modes are similar in structure to the oscillatory longitudinal modes of a laser cavity and arise because of interference of the natural resonant frequency of the oscillator with specific frequencies within the continuum. The spectra revealed departures from linear motion for vigorous vibrations of the oscillator. Each consecutive resonant frequency mode occurred for a movement of the oscillator much less than the wavelength of incident lidar radiation.
Spectral analysis of vibrational harmonic motion by use of a continuous-wave CO2 Doppler lidar.
Jarzembski, M A; Srivastava, V
2000-10-01
Vibrational motion of a harmonic oscillator was investigated with a focused continuous-wave (cw) CO2 Doppler lidar at 9.1-microm wavelength. A continuum of frequencies along with many discrete, equally spaced, resonant frequency modes was observed. The frequency modes are similar in structure to the oscillatory longitudinal modes of a laser cavity and arise because of interference of the natural resonant frequency of the oscillator with specific frequencies within the continuum. Each consecutive resonant frequency mode occurred for a movement of the oscillator much less than the wavelength of incident lidar radiation. For vigorous vibration of the oscillator, the observed spectra may be indicating nonlinear motion. PMID:11028532
Calculation and manipulation of the chirp rates of high-order harmonics
Murakami, M.; Mauritsson, J.; Schafer, K.J.; Gaarde, M.B.; L'Huillier, A.
2005-01-01
We calculate the linear chirp rates of high-order harmonics in argon, generated by intense, 810 nm laser pulses, and explore the dependence of the chirp rate on harmonic order, driving laser intensity, and pulse duration. By using a time-frequency representation of the harmonic fields we can identify several different linear chirp contributions to the plateau harmonics. Our results, which are based on numerical integration of the time-dependent Schroedinger equation, are in good agreement with the adiabatic predictions of the strong field approximation for the chirp rates. Extending the theoretical analysis in the recent paper by Mauritsson et al. [Phys. Rev. A 70, 021801(R) (2004)], we also manipulate the chirp rates of the harmonics by adding a chirp to the driving pulse. We show that the chirp rate for harmonic q is given by the sum of the intrinsic chirp rate, which is determined by the new duration and peak intensity of the chirped driving pulse, and q times the external chirp rate.
NASA Astrophysics Data System (ADS)
Kongsted, Jacob; Christiansen, Ove
2006-09-01
An automatic and general procedure for the calculation of geometrical derivatives of the energy and general property surfaces for molecular systems is developed and implemented. General expressions for an n-mode representation are derived, where the n-mode representation includes only the couplings between n or less degrees of freedom. The general expressions are specialized to derivative force fields and property surfaces, and a scheme for calculation of the numerical derivatives is implemented. The implementation is interfaced to electronic structure programs and may be used for both ground and excited electronic states. The implementation is done in the context of a vibrational structure program and can be used in combination with vibrational self-consistent field (VSCF), vibrational configuration interaction (VCI), vibrational Mller-Plesset, and vibrational coupled cluster calculations of anharmonic wave functions and calculation of vibrational averaged properties at the VSCF and VCI levels. Sample calculations are presented for fundamental vibrational energies and vibrationally averaged dipole moments and frequency dependent polarizabilities and hyperpolarizabilities of water and formaldehyde.
Detection Enhancement of Protein Structural Vibrations: Measurements and Calculations
NASA Astrophysics Data System (ADS)
Niessen, Katherine; Xu, Mengyang; Snell, Edward; Cody, Vivian; Pace, James; Schmidt, Marius; Markelz, Andrea
2015-03-01
Narrow band intramolecular protein vibrations have been successfully measured using crystal anisotropy THz microscopy (CATM), a near-field technique, on protein crystals. To address the question of how these motions are related to protein function we developed a variation of this technique to rapidly measure a variety of protein crystals. The variation anisotropy measurement consists of introducing a wire-grid polarizer in the THz path and rotating the polarizer between measurements, instead of the sample. While the resulting anisotropic spectra confirm reproducibility and protein specific nature of the response the signal is not directly related to the absorption spectra and in fact shows more structure than CATM. This is due to the polarization sensitivity of the electro-optical detection crystal and the changing THz polarization direction and amplitude at the detector. This combination leads to an enhancement of specific resonances and increased sensitivity to rotation of the THz polarization from the sample itself. Preliminary calculations suggest that the technique is sensitive to the birefringence associated with anisotropic absorbance. The results and significance of these measurements on protein and sucrose crystals and the calculated expected response will be discussed.
Calculated vibrational states of ozone up to dissociation.
Ndengu, Steve; Dawes, Richard; Wang, Xiao-Gang; Carrington, Tucker; Sun, Zhigang; Guo, Hua
2016-02-21
A new accurate global potential energy surface for the ground electronic state of ozone [R. Dawes et al., J. Chem. Phys. 139, 201103 (2013)] was published fairly recently. The topography near dissociation differs significantly from previous surfaces, without spurious submerged reefs and corresponding van der Waals wells. This has enabled significantly improved descriptions of scattering processes, capturing the negative temperature dependence and large kinetic isotope effects in exchange reaction rates. The exchange reactivity was found to depend on the character of near-threshold resonances and their overlap with reactant and product wavefunctions, which in turn are sensitive to the potential. Here we present global "three-well" calculations of all bound vibrational states of three isotopic combinations of ozone ((48)O3, (16)O2 (18)O, (16)O2 (17)O) for J = 0 and J = 1 with a focus on the character and density of highly excited states and discuss their impact on the ozone isotopic anomaly. The calculations were done using a parallel symmetry-adapted Lanczos method with the RV3 code. Some comparisons were made with results obtained with the improved relaxation method implemented in the Heidelberg multi-configuration time-dependent Hartree code. PMID:26896981
NASA Astrophysics Data System (ADS)
Godtliebsen, Ian H.; Christiansen, Ove
2015-10-01
It is demonstrated how vibrational IR and Raman spectra can be calculated from damped response functions using anharmonic vibrational wave function calculations, without determining the potentially very many eigenstates of the system. We present an implementation for vibrational configuration interaction and vibrational coupled cluster, and describe how the complex equations can be solved using iterative techniques employing only real trial vectors and real matrix-vector transformations. Using this algorithm, arbitrary frequency intervals can be scanned independent of the number of excited states. Sample calculations are presented for the IR-spectrum of water, Raman spectra of pyridine and a pyridine-silver complex, as well as for the infra-red spectrum of oxazole, and vibrational corrections to the polarizability of formaldehyde.
NASA Astrophysics Data System (ADS)
Stepšys, A.; Mickevicius, S.; Germanas, D.; Kalinauskas, R. K.
2014-11-01
This new version of the HOTB program for calculation of the three and four particle harmonic oscillator transformation brackets provides some enhancements and corrections to the earlier version (Germanas et al., 2010) [1]. In particular, new version allows calculations of harmonic oscillator transformation brackets be performed in parallel using MPI parallel communication standard. Moreover, higher precision of intermediate calculations using GNU Quadruple Precision and arbitrary precision library FMLib [2] is done. A package of Fortran code is presented. Calculation time of large matrices can be significantly reduced using effective parallel code. Use of Higher Precision methods in intermediate calculations increases the stability of algorithms and extends the validity of used algorithms for larger input values. Catalogue identifier: AEFQ_v4_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEFQ_v4_0.html Program obtainable from: CPC Program Library, Queen’s University of Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 Number of lines in programs, including test data, etc.: 1711 Number of bytes in distributed programs, including test data, etc.: 11667 Distribution format: tar.gz Program language used: FORTRAN 90 with MPI extensions for parallelism Computer: Any computer with FORTRAN 90 compiler Operating system: Windows, Linux, FreeBSD, True64 Unix Has the code been vectorized of parallelized?: Yes, parallelism using MPI extensions. Number of CPUs used: up to 999 RAM(per CPU core): Depending on allocated binomial and trinomial matrices and use of precision; at least 500 MB Catalogue identifier of previous version: AEFQ_v1_0 Journal reference of previous version: Comput. Phys. Comm. 181, Issue 2, (2010) 420-425 Does the new version supersede the previous version? Yes Nature of problem: Calculation of matrices of three-particle harmonic oscillator brackets (3HOB) and four-particle harmonic oscillator brackets (4HOB) in a more effective way, which allows us to calculate matrix of the brackets up to a few hundred times more rapidly and more accurate than in a previous version. Solution method: Using external parallelization libraries and mutable precision we created a pack of numerical codes based on the methods of compact expressions of the three and four-particle harmonics oscillator brackets 3HOB, 4HOB, presented in [3]. Restrictions: For double precision version calculations can be done up to harmonic oscillator (HO) energy quanta e=28. For quadruple precision mantissa is equal to approximately 34 decimal digits, therefore calculations can be done up to HO energy quanta to e=52. Running time: The running time depends on the harmonic oscillator energy quanta, cluster size and the precision of intermediate calculations. More information on Table 1 for 3HOB and Table 2 for 4HOB. Reasons for a new version: The new program version expands the limits of harmonic oscillator energy quanta and gives shorter calculation time. Extend the limits of calculation of HOB First version was able to produce harmonic oscillator transformation brackets for three and four particles if E≤HO energy quanta. With this version of our program, if quadruple or arbitrary precision functions are being used, it is possible to calculate three and four particle harmonic oscillator transformation brackets for greater values of energy and momenta, while sustaining tolerable margin of error. Calculation time As the code of previous version of program was redone using parallelism paradigma, it is now possible to reduce the calculation time of transformation matrices significantly, depending on the size of computing cluster, as the dimensions of matrices are growing very rapidly according to the energy and momenta values. subroutinematrix_4HOB_dimensionCalculates the dimension of 4HOB matrix. subroutinematrix_3HOB_dimensionCalculates the dimension of 3HOB matrix, subroutinematrix_3HOBCalculates the global state array which is used in parallel calculation of 3HOB matrix. subroutinematrix_4HOBCalculates the global state array which is used in parallel calculation of 4HOB matrix. subroutinestate_array_3HOBCreates state array for 3HOB matrix output. subroutinestate_array_4HOBCreates state array for 4HOB matrix output. subroutinecalculate_3HOBPerforms parallel calculations of 3HOB matrix. subroutinecalculate_4HOBPerforms parallel calculations of 4HOB matrix. double precision functiondp_4HOBCalculates matrix element for 4HOB. subroutinedp_binomFills the array of binomial coefficients. subroutinedp_trinomFills the array of trinomial coefficients. integer functiontriFunction for triangle condition testing. double precision functiondp_c6jFunction for 6-j coefficient calculation. double precision functiondp_c9jFunction for 9-j coefficient calculation double precision functiondp_kl0Function for Clebsch-Gordan coefficient with zero projection calculation. double precision functiondp_gFunction for gamma element calculation. double precision functiondp_3HOBCalculates three particle harmonic oscillator transformation bracket. type(fm) functionbinomasFunction for calculation of binomial value using FMLIB function Binomial. type(fm) functionaccess_binomFunction for accessing triangular binomial matrix fm_bin. type(fm) functioncheck_binFunction for checking if required binomial value is located in matrix fm_bin. If not, the value is calculated using FMLIB function Binomial. subroutinewrite_binomFunction for writing calculated binomial value to triangular matrix fm_bin.
Variational Calculations of IR Ro-Vibrational Spectra for Nitric Acid
NASA Astrophysics Data System (ADS)
Pavlyuchko, A. I.; Yurchenko, S. N.; Tennyson, J.
2013-09-01
To model the atmospheric composition of the potentially habitable planets, it is essential to have comprehensive data on the spectroscopic properties of the main molecular absorbers. This is especially true in the infrared region which is dominated by transitions of polyatomic molecules [1]. Nitric acid (HNO3) is an important constituent of the Earth atmosphere where it is a prominent bio-signature. Here we present simulations of the absorption spectra for HNO3. We have developed a variational method to solve the ro-vibrational Schrdinger equation for a general polyatomic molecule. The ro-vibrational Hamiltonian is given by [2] where the internal curvilinear vibrational coordinates qi are used to represent the displacements of the bond lengths and bond angles, ?ij(q) are elements of the matrix of the kinematic coefficients, t is the determinant of this matrix, 'a are the Euler angles, and ?ab(q) is the inverse matrix of the tensor of inertia. The potential energy function, V (q), is given by a fourthorder polynomial expansion in terms of Morse variables xi = 1 - e-iqi for the stretching coordinates and xi = qi for the bending coordinates. The dipole moment of the molecule is presented in the form of a Taylor series of the 2nd order in terms of qi. The parameters of the potential energy and the dipole moment functions of HNO3 were calculated by the quantum chemical method at the CCSD(T)/aug-cc-pVQZ level of theory. With this potential energy function, agreement between the calculated and experimental fundamental frequencies of vibrations is within 5 cm -1. The harmonic part of the potential function was then optimized by fitting to the experimental fundamental frequencies and used to simulate the IR spectra of HNO3. The results are in good agreement with the experimental data. The figure shows an example of the simulated spectra of HNO3 in the area of the strong Fermi resonance between the -5 and 2-9 bands along with an experimental counterpart. The resulting line list can be used for modelling atmospheres of (exo)planets at elevated temperatures.
NASA Astrophysics Data System (ADS)
Seyed-Aghazadeh, Banafsheh; Budz, Collin; Modarres-Sadeghi, Yahya
2015-09-01
Vortex-induced vibration (VIV) of a curved circular cylinder (a quarter of a ring, with no extension added to either end) free to oscillate in the crossflow direction was studied experimentally. Both the concave and the convex orientations (with respect to the oncoming flow direction) were considered. As expected, the amplitude of oscillations in both configurations was decreased compared to a vertical cylinder with the same mass ratio. Flow visualizations showed that the vortices were shed in parallel to the curved cylinder, when the cylinder was free to oscillate. The sudden jump in the phase difference between the flow forces and the cylinder displacement observed in the VIV of vertical cylinders was not observed in the curved cylinders. Higher harmonic force components at frequencies twice and three times the frequency of oscillations were observed in flow forces acting on the vertical cylinder, as well as the curved cylinder. Asymmetry in the wake was responsible for the 2nd harmonic force component and the relative velocity of the structure with respect to the oncoming flow was responsible for the 3rd harmonic force component. The lock-in occurred over the same range of reduced velocities for the curved cylinder in the convex orientation as for a vertical cylinder, but it was extended to higher reduced velocities for a curved cylinder in the concave orientation. Higher harmonic force components were found to be responsible for the extended lock-in range in the concave orientation. Within this range, the higher harmonic forces were even larger than the first harmonic force and the structure was being excited mainly by these higher harmonic forces.
Calculation of Raman optical activity spectra for vibrational analysis.
Mutter, Shaun T; Zielinski, Franois; Popelier, Paul L A; Blanch, Ewan W
2015-05-01
By looking back on the history of Raman Optical Activity (ROA), the present article shows that the success of this analytical technique was for a long time hindered, paradoxically, by the deep level of detail and wealth of structural information it can provide. Basic principles of the underlying theory are discussed, to illustrate the technique's sensitivity due to its physical origins in the delicate response of molecular vibrations to electromagnetic properties. Following a short review of significant advances in the application of ROA by UK researchers, we dedicate two extensive sections to the technical and theoretical difficulties that were overcome to eventually provide predictive power to computational simulations in terms of ROA spectral calculation. In the last sections, we focus on a new modelling strategy that has been successful in coping with the dramatic impact of solvent effects on ROA analyses. This work emphasises the role of complementarity between experiment and theory for analysing the conformations and dynamics of biomolecules, so providing new perspectives for methodological improvements and molecular modelling development. For the latter, an example of a next-generation force-field for more accurate simulations and analysis of molecular behaviour is presented. By improving the accuracy of computational modelling, the analytical capabilities of ROA spectroscopy will be further developed so generating new insights into the complex behaviour of molecules. PMID:25646177
NASA Astrophysics Data System (ADS)
Ba?i?, Z.
1991-09-01
We show that the triatomic adiabatic vibrational eigenstates (AVES) provide a convenient basis for accurate discrete variable representation (DVR) calculation and automatic assignment of highly excited, large amplitude motion vibrational states of floppy triatomic molecules. The DVR-AVES states are eigenvectors of the diagonal (in the stretch states) blocks of the adiabatically rearranged triatomic DVR-ray eigenvector (DVR-REV) Hamiltonian [J. C. Light and Z. Ba?i?, J. Chem. Phys. 87, 4008 (1987)]. The transformation of the full triatomic vibrational Hamiltonian from the DVR-REV basis to the new DVR-AVES basis is simple, and does not involve calculation of any new matrix elements. No dynamical approximation is made in the energy level calculation by the DVR-AVES approach; its accuracy and efficiency are identical to those of the DVR-REV method. The DVR-AVES states, as the adiabatic approximation to the vibrational states of a triatomic molecule, are labeled by three vibrational quantum numbers. Consequently, accurate large amplitude motion vibrational levels obtained by diagonalizing the full vibrational Hamiltonian transformed to the DVR-AVES basis, can be assigned automatically by the code, with the three quantum numbers of the dominant DVR-AVES state associated with the largest (by modulus) eigenvector element in the DVR-AVES basis. The DVR-AVES approach is used to calculate accurate highly excited localized and delocalized vibrational levels of HCN/HNC and LiCN/LiNC. A significant fraction of localized states of both systems, below and above the isomerization barrier, is assigned automatically, without inspection of wave function plots or separate approximate calculations.
Full-wave Calculation of Sheared Poloidal Flow Driven by High Harmonic IBW
NASA Astrophysics Data System (ADS)
Jaeger, E. F.; Berry, L. A.; Batchelor, D. B.; Myra, J. R.; D'Ippolito, D. A.
1999-11-01
Recent experiments on FTU and TFTR have used high harmonic ion Bernstein waves (IBW) to drive sheared poloidal flow near the 4th and 5th harmonic ion cyclotron resonances, respectively. Here we apply a new 1-D full-wave code, AORSA (All ORders Spectral Algorithm) to study the propagation and absorption of high harmonic IBW near the 5th harmonic tritium resonance in a deuterium plasma. Several electromagnetic non-linear models for the rf force terms are used to calculate the driven sheared flow. The simplest fluid model approximates the kinetic pressure tensor by a Reynolds stress. An electromagnetic nonlinear eikonal theoryfootnote J.R. Myra and D.A. D'Ippolito, 13th Topical Conference on Applications of Radio Frequency Power to Plasmas, Annapolis, MD, April 12 -14, 1999. (with k _⊥ ρ ~ 1 and k / k unrestricted) calculates the rf force term including the nonlinear kinetic pressure tensor. An alternate kinetic approach(L.A. Berry, E.F. Jaeger, D.B Batchelor, Phys. Rev. Lett. 82, 1871 (1999).) includes the lowest order dependence on the spectral width, δ k.
Time-independent eigenstate-free calculation of vibronic spectra beyond the harmonic approximation.
Petrenko, Taras; Rauhut, Guntram
2015-12-21
The calculation of vibronic spectra and resonance Raman intensities can be performed on the basis of the Raman wavefunction (RWF) formalism. In general, the well-known sum-over-states (SOS) and time-dependent methods can be applied for calculating the RWF. We present an alternative route in which the RWF is determined pointwise in a spectral range on the basis of the inhomogeneous Schrödinger equation using an iterative subspace method, in which explicit state-by-state calculations of vibrational eigenstates are bypassed. We study this approach within the framework of vibrational configuration interaction theory in conjunction with high-level electronic structure calculations for the multidimensional Born-Oppenheimer potential energy surface. The method benefits from an implicit account of interference effects between vibrational states, so that its computational cost correlates with the required resolution in the spectra. The accuracy and efficiency of the method with respect to comparable SOS calculations are tested for the simulation of the photoelectron spectra of ClO2, HS2 (-), ZnOH(-), and Zn(H2O)(+). PMID:26696045
Time-independent eigenstate-free calculation of vibronic spectra beyond the harmonic approximation
NASA Astrophysics Data System (ADS)
Petrenko, Taras; Rauhut, Guntram
2015-12-01
The calculation of vibronic spectra and resonance Raman intensities can be performed on the basis of the Raman wavefunction (RWF) formalism. In general, the well-known sum-over-states (SOS) and time-dependent methods can be applied for calculating the RWF. We present an alternative route in which the RWF is determined pointwise in a spectral range on the basis of the inhomogeneous Schrdinger equation using an iterative subspace method, in which explicit state-by-state calculations of vibrational eigenstates are bypassed. We study this approach within the framework of vibrational configuration interaction theory in conjunction with high-level electronic structure calculations for the multidimensional Born-Oppenheimer potential energy surface. The method benefits from an implicit account of interference effects between vibrational states, so that its computational cost correlates with the required resolution in the spectra. The accuracy and efficiency of the method with respect to comparable SOS calculations are tested for the simulation of the photoelectron spectra of ClO2, HS2 - , ZnOH-, and Zn(H2O)+.
Calculation of optical second-harmonic susceptibilities and optical activity for crystals
Levine, Z.H.
1994-12-31
A new generation of nearly first-principles calculations predicts both the linear and second-harmonic susceptibilities for a variety of insulating crystals, including GaAs, GaP, AlAs, AlP, Se, {alpha}-quartz, and c-urea. The results are typically in agreement with experimental measurements. The calculations have been extended to optical activity, with somewhat less success to date. The theory, based on a simple self-energy correction to the local density approximation, and results are reviewed herein.
Revised calculation of four-particle harmonic-oscillator transformation brackets matrix
NASA Astrophysics Data System (ADS)
Mickevi?ius, S.; Germanas, D.; Kalinauskas, R. K.
2013-02-01
In this article we present a new, considerably enhanced and more rapid method for calculation of the matrix of four-particle harmonic-oscillator transformation brackets (4HOB). The new method is an improved version of 4HOB matrix calculations which facilitates the matrix calculation by finding the eigenvectors of the 4HOB matrix explicitly. Using this idea the new Fortran code for fast and 4HOB matrix calculation is presented. The calculation time decreases more than a few hundred times for large matrices. As many problems of nuclear and hadron physics structure are modeled on the harmonic oscillator (HO) basis our presented method can be useful for large-scale nuclear structure and many-particle identical fermion systems calculations. Program summaryTitle of program: HOTB_M Catalogue identifier: AEFQ_v3_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFQ_v3_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License version 3 No. of lines in distributed program, including test data, etc.: 2149 No. of bytes in distributed program, including test data, etc.: 17576 Distribution format: tar.gz Programming language: Fortran 90. Computer: Any computer with Fortran 90 compiler. Operating system: Windows, Linux, FreeBSD, True64 Unix. RAM: Up to a few Gigabytes (see Tables 1 and 2 included in the distribution package) Classification: 17.16, 17.17. Catalogue identifier of previous version: AEFQ_v2_0 Journal reference of previous version: Comput. Phys. Comm. 182(2011)1377 Does the new version supersede the previous version?: Yes Nature of problem: Calculation of the matrix of the 4HOB in a more effective way, which allows us to calculate the matrix of the brackets up to a few hundred times more rapidly than in a previous version. Solution method: The method is based on compact expressions of 4HOB, presented in [1] and its simplifications presented in this paper. Reasons for new version: We facilitated the calculation of the 4HOB, based on the method presented in the section 'Theoretical aspects'. The new program version gives shorter calculation times for the 4HOB Summary of revisions: New subroutines for calculation of the matrix of the 4HOB. For theoretical issues of revision see the section 'Theoretical aspects'. Restrictions: The 4HOB matrices up to e=28. Running time: Depends on the dimension of the 4HOB matrix (see Tables 1 and 2 included in the distribution file). References: [1] D. Germanas, S. Mickevicius, R.K. Kalinauskas, Calculation of four-particle harmonic-oscillator transformation brackets, Computer Physics Communications 181, 420-425 (2010).
Balachandran, V; Parimala, K
2012-09-01
This study is a comparative analysis of FT-IR and FT-Raman spectra of vanillin (3-methoxy-4-hydroxybenzaldehyde) and isovanillin (3-hydroxy-4-methoxybenzaldehyde). The molecular structure, vibrational wavenumbers, infrared intensities, Raman scattering activities were calculated for both molecules using the B3LYP density functional theory (DFT) with the standard 6-311++G(∗∗) basis set. The computed values of frequencies are scaled using multiple scaling factors to yield good coherence with the observed values. The calculated harmonic vibrational frequencies are compared with experimental FT-IR and FT-Raman spectra. The geometrical parameters and total energies of vanillin and isovanillin were obtained for all the eight conformers (a-h) from DFT/B3LYP method with 6-311++G(∗∗) basis set. The computational results identified the most stable conformer of vanillin and isovanillin as in the "a" form. Non-linear properties such as electric dipole moment (μ), polarizability (α), and hyperpolarizability (β) values of the investigated molecules have been computed using B3LYP quantum chemical calculation. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecules. PMID:22542395
Tang, Xiaoli; Dong, Jianjun
2009-05-01
We report a recent first-principles calculation of harmonic and anharmonic lattice dynamics of MgO. The 2nd order harmonic and 3rd order anharmonic interatomic interaction terms are computed explicitly, and their pressure dependences are discussed. The phonon mode Grueneisen parameters derived based on our calculated 3rd order lattice anharmonicity are in good agreement with those estimated using the finite difference method. The implications for lattice thermal conductivity at high pressure are discussed based on a simple kinetic transport theory.
Liu, Jinfeng; Zhang, John Z H; He, Xiao
2016-01-21
Geometry optimization and vibrational spectra (infrared and Raman spectra) calculations of proteins are carried out by a quantum chemical approach using the EE-GMFCC (electrostatically embedded generalized molecular fractionation with conjugate caps) method (J. Phys. Chem. A, 2013, 117, 7149). The first and second derivatives of the EE-GMFCC energy are derived and employed in geometry optimization and vibrational frequency calculations for several test systems, including a polypeptide ((GLY)6), an ?-helix (AKA), a ?-sheet (Trpzip2) and ubiquitin (76 residues with 1231 atoms). Comparison of the present results with those obtained from full system QM (quantum mechanical) calculations shows that the EE-GMFCC approach can give accurate molecular geometries, vibrational frequencies and vibrational intensities. The EE-GMFCC method is also employed to simulate the amide I vibration of proteins, which has been widely used for the analysis of peptide and protein structures, and the results are in good agreement with the experimental observations. PMID:26686896
Miller, Y; Chaban, G M; Gerber, R B
2005-07-28
Vibrational frequencies for fundamental, overtone, and combination excitations of sulfuric acid (H2SO4) and of sulfuric acid monohydrate cluster (H2SO4 x H2O) are computed directly from ab initio MP2/TZP potential surface points using the correlation-corrected vibrational self-consistent field (CC-VSCF) method, which includes anharmonic effects. The results are compared with experiment. The computed transitions show in nearly all cases good agreement with experimental data and consistent improvement over the harmonic approximation. The CC-VSCF improvements over the harmonic approximation are largest for the overtone and combination excitations and for the OH stretching fundamental. The agreement between the calculations and experiment also supports the validity of the MP2/TZP potential surfaces. Anharmonic coupling between different vibrational modes is found to significantly affect the vibrational frequencies. Analysis of the mean magnitude of the anharmonic coupling interactions between different pairs of normal modes is carried out. The results suggest possible mechanisms for the internal flow of vibrational energy in H2SO4 and H2SO4 x H2O. PMID:16834003
Thompson, Lee M; Lasoroski, Aurlie; Champion, Paul M; Sage, J Timothy; Frisch, Michael J; van Thor, Jasper J; Bearpark, Michael J
2014-02-11
A systematic comparison of different environmental effects on the vibrational modes of the 4-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI) chromophore using the ONIOM method allows us to model how the molecule's spectroscopic transitions are modified in the Green Fluorescent Protein (GFP). ONIOM(QM:MM) reduces the expense of normal mode calculations when computing the majority of second derivatives only at the MM level. New developments described here for the efficient solution of the CPHF equations, including contributions from electrostatic interactions with environment charges, mean that QM model systems of ?100 atoms can be embedded within a much larger MM environment of ?5000 atoms. The resulting vibrational normal modes, their associated frequencies, and dipole derivative vectors have been used to interpret experimental difference spectra (GFPI2-GFPA), chromophore vibrational Stark shifts, and changes in the difference between electronic and vibrational transition dipoles (mode angles) in the protein environment. PMID:26580050
NASA Astrophysics Data System (ADS)
Li, Mingfeng; Lim, Teik C.; Shepard, W. Steve, Jr.; Guan, Y. H.
2005-10-01
An experimental study of an active shaft transverse vibration control system for suppressing gear mesh vibratory response due to transmission error excitation in a high power density gearbox is presented. The proposed active control concept employs a piezoelectric stack actuator to deliver the control force through a secondary bearing. A versatile test stand that includes a closed-loop, power recirculating, dual-gearbox set-up capable of high load transfer is specially designed for this work. The underlying controller for computing the actuation signal is based on a modified filtered-x LMS algorithm with a robust frequency estimation technique. In order to avoid the common out-of-band overshoot problem, an integrated adaptive linear enhancer is also applied. Both single mesh frequency and multi-harmonic control cases are examined to evaluate the performance of the active control system. Additionally, the impact of the adaptive linear enhancer order as well as the controller adaptation step size on active control performance is evaluated. The experiments performed show more than 10 dB reduction in housing vibrations at certain targeted mesh harmonics over a range of operating speeds.
NASA Astrophysics Data System (ADS)
Deodhar, Bhushan S.; Brenner, Reid E.; Klaassen, Joshua J.; Tubergen, Michael J.; Durig, James R.
2015-09-01
The infrared and Raman spectra (3200-50 cm-1) of the gas, liquid or solution, and solid of fluoroacetyl chloride, FCH2COCl have been recorded. FT-microwave studies have also been carried out and 22 transitions were recorded for the trans conformer. Variable temperature (-50 to -105 °C) studies of the infrared and Raman spectra (3200-50 cm-1) of xenon solutions have been carried out. From these data, the trans, cis and gauche conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 159 ± 11 cm-1 (1.90 ± 0.14 kJ mol-1) with the trans conformer the more stable form than the cis. The energy difference between the cis and gauche form is 222 ± 18 cm-1 (2.66 ± 0.21 kJ/mol) and the energy difference between the trans and gauche forms is 386 ± 13 cm-1 (4.61 ± 0.16 kJ/mol). Vibrational assignments have been made for the observed bands for the three conformers with initial predictions by MP2(full)/6-31G(d) ab initio calculations to obtain harmonic force constants, wavenumbers, infrared intensities, and Raman activities for the three conformers. By utilizing the microwave rotational constants of two isotopomers for trans, combined with the structural parameters predicted from MP2(full)/6-311+G(d,p) calculations, adjusted r0 parameters have been obtained for the trans conformer. The results are discussed and compared to the corresponding properties of some related molecules.
Deodhar, Bhushan S; Brenner, Reid E; Klaassen, Joshua J; Tubergen, Michael J; Durig, James R
2015-09-01
The infrared and Raman spectra (3200-50 cm(-1)) of the gas, liquid or solution, and solid of fluoroacetyl chloride, FCH2COCl have been recorded. FT-microwave studies have also been carried out and 22 transitions were recorded for the trans conformer. Variable temperature (-50 to -105 C) studies of the infrared and Raman spectra (3200-50 cm(-1)) of xenon solutions have been carried out. From these data, the trans, cis and gauche conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 15911 cm(-1) (1.900.14 kJ mol(-1)) with the trans conformer the more stable form than the cis. The energy difference between the cis and gauche form is 22218 cm(-1) (2.660.21 kJ/mol) and the energy difference between the trans and gauche forms is 38613 cm(-1) (4.610.16 kJ/mol). Vibrational assignments have been made for the observed bands for the three conformers with initial predictions by MP2(full)/6-31G(d) ab initio calculations to obtain harmonic force constants, wavenumbers, infrared intensities, and Raman activities for the three conformers. By utilizing the microwave rotational constants of two isotopomers for trans, combined with the structural parameters predicted from MP2(full)/6-311+G(d,p) calculations, adjusted r0 parameters have been obtained for the trans conformer. The results are discussed and compared to the corresponding properties of some related molecules. PMID:25909903
NASA Astrophysics Data System (ADS)
Diniz, Leonardo G.; Mohallem, Jos Rachid; Alijah, Alexander; Pavanello, Michele; Adamowicz, Ludwik; Polyansky, Oleg L.; Tennyson, Jonathan
2013-09-01
Using the core-mass approach, we have generated a vibrational-mass surface for the triatomic H3+. The coordinate-dependent masses account for the off-resonance nonadiabatic coupling and permit a very accurate determination of the rovibrational states using a single potential energy surface. The new, high-precision measurements of 12 rovibrational transitions in the ?2 bending fundamental of H3+ by Wu [Phys. Rev. A1050-294710.1103/PhysRevA.88.032507 88, 032507 (2013)] are used to scale this surface empirically and to derive state-dependent vibrational and rotational masses that reproduce the experimental transition energies to 10-3cm-1. Rotational term values for J?10 are presented for the two lowest vibrational states and equivalent transitions in D3+ considered.
Wang, Liang; Liu, Weimin; Fang, Chong
2015-07-14
Low-frequency vibrations are foundational for material properties including thermal conductivity and chemical reactivity. To resolve the intrinsic molecular conformational dynamics in condensed phase, we implement time-resolved third-harmonic generation (TRTHG) spectroscopy to unravel collective skeletal motions in calcite, water, and aqueous salt solution in situ. The lifetime of three Raman-active modes in polycrystalline calcite at 155, 282 and 703 cm(-1) is found to be ca. 1.6 ps, 1.3 ps and 250 fs, respectively. The lifetime difference is due to crystallographic defects and anharmonic effects. By incorporating a home-built wire-guided liquid jet, we apply TRTHG to investigate pure water and ZnCl2 aqueous solution, revealing ultrafast dynamics of water intermolecular stretching and librational bands below 500 cm(-1) and a characteristic 280 cm(-1) vibrational mode in the ZnCl4(H2O)2(2-) complex. TRTHG proves to be a compact and versatile technique that directly uses the 800 nm fundamental laser pulse output to capture ultrafast low-frequency vibrational motion snapshots in condensed-phase materials including the omnipresent water, which provides the important time dimension to spectral characterization of molecular structure-function relationships. PMID:26062639
Hiremath, C S; Kalkoti, G B; Aralakkanavar, M K
2009-09-15
In the present study, a systematic vibrational spectroscopic investigation for the experimental IR and Raman spectra of 2,3,4-trifluorobenzonitrile (TFB), aided by electronic structure calculations has been carried out. The electronic structure calculations -ab initio (RHF) and hybrid density functional methods (B3LYP) - have been performed with 6-31G* basis set. Molecular equilibrium geometries, electronic energies, IR intensities, harmonic vibrational frequencies, depolarization ratios and Raman activities have been computed. The results of the calculations have been used to simulate IR and Raman spectra for TFB that showed excellent agreement with the observed spectra. Potential energy distribution (PED) and normal mode analysis have also been performed. The assignments proposed based on the experimental IR and Raman spectra have been reviewed. A complete assignment of the observed spectra has been proposed. PMID:19560961
NASA Astrophysics Data System (ADS)
Hiremath, C. S.; Kalkoti, G. B.; Aralakkanavar, M. K.
2009-09-01
In the present study, a systematic vibrational spectroscopic investigation for the experimental IR and Raman spectra of 2,3,4-trifluorobenzonitrile (TFB), aided by electronic structure calculations has been carried out. The electronic structure calculations - ab initio (RHF) and hybrid density functional methods (B3LYP) - have been performed with 6-31G* basis set. Molecular equilibrium geometries, electronic energies, IR intensities, harmonic vibrational frequencies, depolarization ratios and Raman activities have been computed. The results of the calculations have been used to simulate IR and Raman spectra for TFB that showed excellent agreement with the observed spectra. Potential energy distribution (PED) and normal mode analysis have also been performed. The assignments proposed based on the experimental IR and Raman spectra have been reviewed. A complete assignment of the observed spectra has been proposed.
Mathammal, R; Monisha, N R; Yasaswini, S; Krishnakumar, V
2015-03-15
In this work, the vibrational spectral analysis is carried out by using Raman and infrared spectroscopy in the range 4000-400 cm(-1) and 4000-50 cm(-1) respectively for N,N-Diphenyl Formamide (DPF) molecule. The optimized molecular structures, vibrational frequencies and corresponding vibrational assignments, nuclear magnetic resonance (NMR) and ultraviolet-visible (UV-VIS) spectra of the title molecule are evaluated using density functional theory (DFT) with standard B3LYP/6-31G(d,p) basis set. The harmonic vibrational frequencies are calculated and the scaled values have been compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The stability of the molecule arising from hyper conjugative interactions and the charge delocalization has been analyzed using natural bond (NBO) analysis. The possible electronic transitions are determined by HOMO-LUMO orbital shapes and their energies. Thermodynamic properties (heat capacity, entropy and enthalpy) and the first hyperpolarizability of the title compound are calculated. The Mulliken charges and electric dipole moment of the molecule are computed using DFT calculations. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shift of the molecules are calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. PMID:25579654
NASA Technical Reports Server (NTRS)
Sopher, R.; Twomey, W. J.
1990-01-01
NASA-Langley is sponsoring a rotorcraft structural dynamics program with the objective to establish in the U.S. a superior capability to utilize finite element analysis models for calculations to support industrial design of helicopter airframe structures. In the initial phase of the program, teams from the major U.S. manufacturers of helicopter airframes will apply extant finite element analysis methods to calculate loads and vibrations of helicopter airframes, and perform correlations between analysis and measurements. The aforementioned rotorcraft structural dynamics program was given the acronym DAMVIBS (Design Analysis Method for Vibrations). Sikorsky's RDYNE Rotorcraft Dynamics Analysis used for the correlation study, the specifics of the application of RDYNE to the AH-1G, and comparisons of the predictions of the method with flight data for loads and vibrations on the AH-1G are described. RDYNE was able to predict trends of variations of loads and vibrations with airspeed, but in some instances magnitudes differed from measured results by factors of two or three to one. Sensitivities were studied of predictions to rotor inflow modeling, effects of torsional modes, number of blade bending modes, fuselage structural damping, and hub modal content.
Premkumar, S; Jawahar, A; Mathavan, T; Kumara Dhas, M; Sathe, V G; Milton Franklin Benial, A
2014-08-14
The molecular structure of 2-(tert-butoxycarbonyl (Boc) -amino)-5-bromopyridine (BABP) was optimized by the DFT/B3LYP method with 6-311G (d,p), 6-311++G (d,p) and cc-pVTZ basis sets using the Gaussian 09 program. The most stable optimized structure of the molecule was predicted by the DFT/B3LYP method with cc-pVTZ basis set. The vibrational frequencies, Mulliken atomic charge distribution, frontier molecular orbitals and thermodynamical parameters were calculated. These calculations were done at the ground state energy level of BABP without applying any constraint on the potential energy surface. The vibrational spectra were experimentally recorded using Fourier Transform-Infrared (FT-IR) and micro-Raman spectrometer. The computed vibrational frequencies were scaled by scale factors to yield a good agreement with observed experimental vibrational frequencies. The complete theoretically calculated and experimentally observed vibrational frequencies were assigned on the basis of Potential Energy Distribution (PED) calculation using the VEDA 4.0 program. The vibrational modes assignments were performed by using the animation option of GaussView 05 graphical interface for Gaussian program. The Mulliken atomic charge distribution was calculated for BABP molecule. The molecular reactivity and stability of BABP were also studied by frontier molecular orbitals (FMOs) analysis. PMID:24727165
NASA Astrophysics Data System (ADS)
Premkumar, S.; Jawahar, A.; Mathavan, T.; Kumara Dhas, M.; Sathe, V. G.; Milton Franklin Benial, A.
2014-08-01
The molecular structure of 2-(tert-butoxycarbonyl (Boc) -amino)-5-bromopyridine (BABP) was optimized by the DFT/B3LYP method with 6-311G (d,p), 6-311++G (d,p) and cc-pVTZ basis sets using the Gaussian 09 program. The most stable optimized structure of the molecule was predicted by the DFT/B3LYP method with cc-pVTZ basis set. The vibrational frequencies, Mulliken atomic charge distribution, frontier molecular orbitals and thermodynamical parameters were calculated. These calculations were done at the ground state energy level of BABP without applying any constraint on the potential energy surface. The vibrational spectra were experimentally recorded using Fourier Transform-Infrared (FT-IR) and micro-Raman spectrometer. The computed vibrational frequencies were scaled by scale factors to yield a good agreement with observed experimental vibrational frequencies. The complete theoretically calculated and experimentally observed vibrational frequencies were assigned on the basis of Potential Energy Distribution (PED) calculation using the VEDA 4.0 program. The vibrational modes assignments were performed by using the animation option of GaussView 05 graphical interface for Gaussian program. The Mulliken atomic charge distribution was calculated for BABP molecule. The molecular reactivity and stability of BABP were also studied by frontier molecular orbitals (FMOs) analysis.
NASA Astrophysics Data System (ADS)
Mancini, John S.; Bowman, Joel M.
2013-10-01
We present an on-the-fly quantum mechanical method to obtain anharmonic vibrational frequencies for molecular clusters. The basis for the method is the local-monomer model, a "divide and conquer" approach to theoretical spectroscopy, previously applied using full-dimensional surfaces [Y. Wang and J. M. Bowman, J. Chem. Phys. 134, 154510 (2011)]. The model consists of performing a local normal-mode analysis for each monomer in a cluster in the field of the surrounding monomers. Anharmonic vibrational frequencies are then determined for each monomer by numerically solving the Schrdinger equation in terms of the local coordinates using ab initio energies obtained directly. Residual monomer-monomer coupling is accounted for using the Hckel-coupling extension [Y. Wang and J. M. Bowman, J. Chem. Phys. 136, 144113 (2012)]. In addition to the direct local-monomer approach, we propose and demonstrate a composite ab initio technique to reduce computational costs for calculating the anharmonic frequencies of large clusters. This technique utilizes two ab initio methods, a lower level of theory to compute geometries and perform harmonic analyses and a subsequent higher level of theory to compute the energies used in the anharmonic frequency calculations. We demonstrate the on-the-fly approach on hydrogen chloride clusters ranging in size from the dimer to the hexamer. Comparisons of the theoretical frequencies are made to previous experiments. We find the method to be an effective and computationally efficient approach to compute anharmonic frequencies.
Boyarinov, V. F.; Davidenko, V. D.; Polismakov, A. A.; Tsibulsky, V. F.
2006-07-01
Development of the SUHAM-U code for burnup calculations of VVER-1000 fuel assemblies with uranium and MOX fuel is described. Developed SUHAM-U code has capacity to calculate burnup in each fuel or poison zone of each cell of VVER-1000 fuel assembly. In so doing Surface Harmonics Method is used for calculation of the detail neutron spectra in fuel assembly at separated burnup values. Verification of SUHAM-U code by burnup calculations of VVER-1000 fuel assemblies with uranium and MOX fuel has been carried out. Comparisons were carried out with calculations by UNK and RECOL codes. UNK code uses the first collisions probabilities method for solution of the neutron transport equation and RECOL code uses Monte-Carlo method with point-wise continues energy presentation of cross-sections. The main conclusion of all comparisons is the SUHAM-U code calculates the fuel burnup of VVER-1000 fuel assemblies with uranium and MOX fuel with enough high accuracy. Time expenditures are adduced. (authors)
Nonlinear vibrational excitations in molecular crystals molecular mechanics calculations
NASA Astrophysics Data System (ADS)
Pumilia, P.; Abbate, S.; Baldini, G.; Ferro, D. R.; Tubino, R.
1992-03-01
The coupling constant for vibrational solitons χ has been examined in a molecular mechanics model for acetanilide (ACN) molecular crystal. According to A.C. Scott, solitons can form and propagate in solid acetanilide over a threshold energy value. This can be regarded as a structural model for the spines of hydrogen bond chains stabilizing the α helical structure of proteins. A one dimensional hydrogen bond chain of ACN has been built, for which we have found that, even though experimental parameters are correctly predicted, the excessive rigidity of the isolated chain prevents the formation of a localized distortion around the excitation. Yet, C=O coupling value with softer lattice modes could be rather high, allowing self-trapping to take place.
Arapiraca, A F C; Jonsson, Dan; Mohallem, J R
2011-12-28
We report an upgrade of the Dalton code to include post Born-Oppenheimer nuclear mass corrections in the calculations of (ro-)vibrational averages of molecular properties. These corrections are necessary to achieve an accuracy of 10(-4) debye in the calculations of isotopic dipole moments. Calculations on the self-consistent field level present this accuracy, while numerical instabilities compromise correlated calculations. Applications to HD, ethane, and ethylene isotopologues are implemented, all of them approaching the experimental values. PMID:22225162
Sawant, Dattatray K; Klaassen, Joshua J; Gounev, Todor K; Durig, James R
2015-12-01
The infrared and Raman spectra (3100-50 cm(-1)) of the gas, liquid or solution, and solid have been recorded of cyanocyclopentane, c-C5H9CN. Variable temperature (-60 to -100C) studies of the infrared spectra (3100-400cm(-1)) of the sample dissolved in liquid xenon have been carried out. From these data, both the envelope-equatorial (Eq) and Ax conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 55 12 cm(-1) (0.66 0.14 kJ/mol) with the Eq conformer the more stable form. The percentage of the Ax conformer is estimated to be 451% at ambient temperature. The conformational stabilities have been predicted from ab initio calculations by utilizing several different basis sets up to aug-cc-pVTZ from both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been made for the observed bands for both conformers with initial predictions by MP2(full)/6-31G(d) ab initio calculations to obtain harmonic force constants, wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. The r0 structural parameter values for the Eq[Ax] form are; for the heavy atom distances (): CN=1.160 [1.160] (3); C?-C=1.463 [1.463] (3); C?-C?, C?'=1.543 [1.545] (3); C?-C?, C?'=1.540 [1.541] (3); C?-C?'=1.552 [1.553] (3) and angles (): ?C?-CN=179.0 [178.9] (5); ?C?C?-C=113.1 [110.1] (5); ?C?C?C?'=103.0 [102.1] (5); ?C?C?C?=104.1 [104.8] (5); ?C?C?C?'=106.3 [106.0] (5). The results are discussed and compared to the corresponding properties of some related molecules. PMID:26151436
NASA Astrophysics Data System (ADS)
Durig, James R.; Klaassen, Joshua J.; Sawant, Dattatray K.; Deodhar, Bhushan S.; Panikar, Savitha S.; Gurusinghe, Ranil M.; Darkhalil, Ikhlas D.; Tubergen, Michael J.
2015-02-01
The infrared and Raman spectra (3200-50 cm-1) of the gas, liquid or solution, and solid have been recorded of isocyanocyclopentane, c-C5H9NC. FT-microwave studies have also been carried out and 23 transitions were recorded for the envelope-axial (Ax) conformer. Variable temperature (-65 to -100 °C) studies of the infrared spectra (3200-400 cm-1) dissolved in liquid xenon have been carried out. From these data, both the Ax and envelope-equatorial (Eq) conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 102 ± 10 cm-1 (1.21 ± 0.11 kJ mol-1) with the Ax conformer the more stable form. The percentage of the Eq conformer is estimated to be 38 ± 1% at ambient temperature. The conformational stabilities have been predicted from ab initio calculations by utilizing several different basis sets up to aug-cc-pVTZ from both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been made for the observed bands for both conformers with initial predictions by MP2(full)/6-31G(d) ab initio calculations to obtain harmonic force constants, wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. The structural parameter values for the Ax form are; for the heavy atom distances (Å): Ctbnd N = 1.176 (3); Cαsbnd N = 1.432 (3); Cαsbnd Cβ,Cβ‧ = 1.534 (3); Cβsbnd Cγ,Cγ‧ = 1.542 (3); Cγsbnd Cγ‧ = 1.554 (3) and angles (°): ∠Cαsbnd Ntbnd C = 177.8 (5); ∠CβCαsbnd N = 110.4 (5); ∠CβCαCβ‧ = 102.9 (5); ∠CαCβCγ = 103.6 (5); ∠CβCγCγ‧ = 105.9 (5). The results are discussed and compared to the corresponding properties of some related molecules.
Tuning natural modes of vibration by prestress in the design of a harmonic gong.
McLachlan, Neil; Adams, Ryan; Burvill, Colin
2012-01-01
Prestresses are purposefully added to an object to improve its performance, such as tuning a guitar string by adding tension. This paper reports how the normal modes of a sheet metal component can be tuned through the prestresses generated by cold-forging small dimples. Finite element analysis showed that the frequencies of specific mode shapes were differentially affected by the location of residual stress fields due to dimple formation in relation to modal stress fields. The frequencies of overtones were most sensitive to the depth of the dimples located near the maxima of modal stresses. Using this approach a series of musical gongs were designed with up to the first five overtones tuned to within 5% of the harmonic series. The balance of harmonic and inharmonic overtones in these gongs that are well resolved by the human cochlea may constitute a set of recognizable musical timbres with sufficient harmonicity to produce an unambiguous pitch for most listeners. Since many other mechanical properties of sheet metal components are affected by residual stresses this manufacturing technique may have broader application in design engineering. PMID:22280715
Reactive scattering calculations for D + H2 in vibrationally excited states at ultralow temperature
NASA Astrophysics Data System (ADS)
Simbotin, Ion; Coté, Robin
2006-05-01
We calculate total cross sections for the D + H2(v,j ) collision, and investigate their dependence on the vibrational quantum number v of the initial state of H2. The cross sections increase quasi-exponentially with the excitation energy of the initial vibrational state. This is similar to the exponential dependence observed in the vibrational predissociation of van der Waals complexes. We attempt to explain this simple relationship in terms of the short range details of the single channel atom--molecule wavefunctions and the couplings between the initial and final channels.
A computationally efficient software application for calculating vibration from underground railways
NASA Astrophysics Data System (ADS)
Hussein, M. F. M.; Hunt, H. E. M.
2009-08-01
The PiP model is a software application with a user-friendly interface for calculating vibration from underground railways. This paper reports about the software with a focus on its latest version and the plans for future developments. The software calculates the Power Spectral Density of vibration due to a moving train on floating-slab track with track irregularity described by typical values of spectra for tracks with good, average and bad conditions. The latest version accounts for a tunnel embedded in a half space by employing a toolbox developed at K.U. Leuven which calculates Green's functions for a multi-layered half-space.
NASA Technical Reports Server (NTRS)
Ehlers, F. E.; Weatherill, W. H.; Yip, E. L.
1984-01-01
A finite difference method to solve the unsteady transonic flow about harmonically oscillating wings was investigated. The procedure is based on separating the velocity potential into steady and unsteady parts and linearizing the resulting unsteady differential equation for small disturbances. The differential equation for the unsteady velocity potential is linear with spatially varying coefficients and with the time variable eliminated by assuming harmonic motion. An alternating direction implicit procedure was investigated, and a pilot program was developed for both two and three dimensional wings. This program provides a relatively efficient relaxation solution without previously encountered solution instability problems. Pressure distributions for two rectangular wings are calculated. Conjugate gradient techniques were developed for the asymmetric, indefinite problem. The conjugate gradient procedure is evaluated for applications to the unsteady transonic problem. Different equations for the alternating direction procedure are derived using a coordinate transformation for swept and tapered wing planforms. Pressure distributions for swept, untaped wings of vanishing thickness are correlated with linear results for sweep angles up to 45 degrees.
Calculation of vibrational spectra of an icosahedral quasicrystal AlCuFe
Rudenko, A. N. Mazurenko, V. G.
2007-11-15
Vibrational spectra of an icosahedral quasicrystal AlCuFe have been calculated on the basis of a crystalline 1/1 approximant by the recurrence method. To describe the interaction of atoms in a quasicrystal, the semiempirical EAM model was used. It is shown that the calculated spectra are in satisfactory agreement with the experimental neutron inelastic scattering data.
Anharmonic vibrational studies of L-aspartic acid using HF and DFT calculations
NASA Astrophysics Data System (ADS)
Alam, Mohammad Jane; Ahmad, Shabbir
2012-10-01
The experimental and theoretical studies on the structure, molecular properties and vibrational spectra of L-aspartic acid are presented. The molecular structure, harmonic and anharmonic vibrational frequencies, molecular properties, MEP mapping, NBO analysis and electronic spectra of L-aspartic acid have been reported. Computed geometrical parameters and anharmonic frequencies of fundamental, combination and overtone transitions were found in satisfactory agreement with the experimental data. The UV-Vis spectrum of present molecule has been recorded and the electronic properties such as HOMO and LUMO energies and few low lying excited states were carried out by using time dependent density functional theory (TD-DFT) approach. Natural Bond Orbital (NBO) analysis has been performed for analyzing charge delocalization throughout the molecule. Molecular electrostatic potential map has also been used for quantitative measure of the chemical activities of various sites of the molecule.
NASA Astrophysics Data System (ADS)
Moutinho, Carlos
2015-05-01
This paper is focused on the control problems related to semi-active tuned mass dampers (TMDs) used to reduce harmonic vibrations, specially involving civil structures. A simplified version of the phase control law is derived and its effectiveness is investigated and evaluated. The objective is to improve the functioning of control systems of this type by simplifying the measurement process and reducing the number of variables involved, making the control system more feasible and reliable. Because the control law is of ON/OFF type, combined with appropriate trigger conditions, the activity of the actuation system may be significantly reduced, which may be of few seconds a day in many practical cases, increasing the durability of the device and reducing its maintenance. Moreover, due to the ability of the control system to command the motion of the inertial mass, the semi-active TMD is relatively insensitive to its initial tuning, resulting in the capability of self-tuning and in the possibility of controlling several vibration modes of a structure over a significant broadband frequency.
RESEARCH NOTE: On the efficient calculation of ordinary and generalized spherical harmonics
NASA Astrophysics Data System (ADS)
Masters, Guy; Richards-Dinger, Keith
1998-10-01
Algorithms for the stable computation of generalized and ordinary spherical harmonics are presented. The algorithms are fast and have the useful property that they can compute harmonics for isolated harmonic degrees. fortran and C programs implementing these algorithms are available from the authors.
OJ287: Post-Newtonian Calculation in Harmonic Coordinate and Pulsar Timing Residual Confirmation
NASA Astrophysics Data System (ADS)
Cheng, Bin; Zhang, Yang
2015-07-01
We calculate and discuss the motion of the binary black hole OJ287 based on Post-Newtonian approximation in a harmonic coordinate. With gravitational waveform obtained, theoretical timing residual of PSR B1855+09 induced by gravitational radiation of OJ287 is presented and compared with observed data, further shows that hypothesis referring to OJ287 as a binary BH system might be proper. The energy flux of gravitational radiation from binary is also provided, from which we find that the flux changes sign successively: ĖN > 0, Ė1PN < 0, Ė2PN > 0, in agreement with the relative signs of forces of each PN order, revealed in the previous work. Supported by National Natural Science Foundation of China under Grant Nos. 11275187, 11421303, and the Strategic Priority Research Program “The Emergence of Cosmological Structures” of the Chinese Academy of Sciences under Grant No. XDB09000000
Moro, A. M.; Arias, J. M.; Gomez-Camacho, J.; Perez-Bernal, F.
2009-11-15
A new method for continuum discretization in continuum-discretized coupled-channels calculations is proposed. The method is based on an analytic local-scale transformation of the harmonic-oscillator wave functions proposed for other purposes in a recent work [Karatagladis et al., Phys. Rev. C 71, 064601 (2005)]. The new approach is compared with the standard method of continuum discretization in terms of energy bins for the reactions d+{sup 58}Ni at 80 MeV, {sup 6}Li+{sup 40}Ca at 156 MeV, and {sup 6}He+{sup 208}Pb at 22 MeV and 240 MeV/nucleon. In all cases very good agreement between both approaches is found.
NASA Astrophysics Data System (ADS)
Liu, Shuai; Zhang, Guo-Yong; He, Zhiwei; Zhan, Meng
2015-06-01
The parameter diversity effect in coupled nonidentical elements has attracted persistent interest in nonlinear dynamics. Of fundamental importance is the so-called optimal configuration problem for how the spatial position of elements with different parameters precisely determines the dynamics of the whole system. In this work, we study the optimal configuration problem for the vibration spectra in the classical mass-spring model with a ring configuration, paying particular attention to how the configuration of different masses affects the second smallest vibration frequency ( ? 2) and the largest one ( ? N ). For the extreme values of ? 2 and ? N , namely, ( ? 2)min, ( ? 2)max, ( ? N )min, and ( ? N )max, we find some explicit organization rules for the optimal configurations and some approximation rules when the explicit organization rules are not available. The different distributions of ? 2 and ? N are compared. These findings are interesting and valuable for uncovering the underlying mechanism of the parameter diversity effect in more general cases.
NASA Astrophysics Data System (ADS)
Moorthy, N.; Jobe Prabakar, P. C.; Ramalingam, S.; Periandy, S.; Parasuraman, K.
2016-04-01
In order to explore the unbelievable NLO property of prepared Benzophenone thiosemicarbazone (BPTSC), the experimental and theoretical investigation has been made. The theoretical calculations were made using RHF and CAM-B3LYP methods at 6-311++G(d,p) basis set. The title compound contains Cdbnd S ligand which helps to improve the second harmonic generation (SHG) efficiency. The molecule has been examined in terms of the vibrational, electronic and optical properties. The entire molecular behavior was studied by their fundamental IR and Raman wavenumbers and was compared with the theoretical aspect. The molecular chirality has been studied by performing vibrational circular dichroism (circularly polarized infrared radiation). The Mulliken charge levels of the compound ensure the perturbation of atomic charges according to the ligand. The molecular interaction of frontier orbitals emphasizes the modification of chemical properties of the compound through the reaction path. The enormous amount of NLO activity was induced by the Benzophenone in thiosemicarbazone. The Gibbs free energy was evaluated at different temperature and from which the enhancement of chemical stability was stressed. The VCD spectrum was simulated and the optical dichroism of the compound has been analyzed.
Assessment of CCSD(T)-F12 Approximations and Basis Sets for Harmonic Vibrational Frequencies.
Martin, Jan M L; Kesharwani, Manoj K
2014-05-13
We consider basis set convergence and the effect of various approximations to CCSD(T)-F12 for a representative sample of harmonic frequencies (the HFREQ2014 set). CCSD(T*)(F12*)/cc-pVDZ-F12 offers a particularly favorable compromise between accuracy and computational cost: its RMSD <3 cm(-1) from the valence CCSD(T) limit is actually less than the remaining discrepancy with the experimental value at the valence CCSD(T) limit (about 5 cm(-1) RMSD). CCSD(T)-F12a and CCSD(T)-F12b appear to benefit from error compensation between CCSD and (T). PMID:26580535
Rittiger, J.; Kulicke, B.
1995-10-01
In order to study the effects of large HVDC converters to the feeding ac networks, it is of importance to explain and to calculate harmonic phenomena which are a result of converter operation. During commissioning of real HVDC converters it could be seen, that harmonics resulting from unsymmetries in the system voltages or from unsymmetries in converter operation led to significant difficulties concerning the system design. For this reason, not only the effects of characteristic but also the effects of noncharacteristic converter harmonics must be taken into account. The aim is to describe the steady state harmonic behavior of the converter. The harmonic spectra are not determined by time domain analysis but instead the solution is found by frequency domain calculations. This can result in reduced calculation time in comparison to conventional fourier analysis of the time functions. The converter is interpreted as an amplitude modulator with voltage and current converter functions which describe the coupling of the dc circuit and the ac network through the converter. To verify the theory, comparison of frequency domain with time domain calculations were carried out.
Finite Element Analysis of Forced Vibration for a Pipe Conveying Harmonically Pulsating Fluid
NASA Astrophysics Data System (ADS)
Seo, Young Soo; Jeong, Weui Bong; Jeong, Seok Hyeon; Oh, Jun Suk; Yoo, Wan Suk
It is well known that the natural frequencies of a pipe become lower as uniform internal fluid velocity increases. The pipe becomes unstable if the fluid is faster than the critical velocity. But in the case of a pipe conveying harmonically pulsating fluid, resonances will occur even though the mean velocity of the fluid is below the critical velocity. Therefore, for improved analysis, the effects of pulsating fluid in the pipe should also be taken into consideration. In this study, a finite element formulation for the pipe was carried out while taking into consideration the effects of the fluid pulsating harmonically in the pipe. The damping and stiffness matrices in the finite element equation vary with time. A stability analysis based on the Bolotin method was carried out. And, a method to directly estimate the forced response of the pipe that does not need to solve a time data from time-variant system is presented. Several numerical examples are given in this paper that validate of this method.
van Neer, Paul L M J; Blaak, Sandra; Bosch, Johan G; Lance, Charles T; Prins, Christian; van der Steen, Anton F W; de Jong, Nico
2012-10-01
Transesophageal echocardiography (TEE) uses the esophagus as an imaging window to the heart. This enables cardiac imaging without interference from the ribs or lungs and allows for higher frequency ultrasound to be used compared with transthoracic echocardiography (TTE). TEE facilitates the successful imaging of obese or elderly patients, where TTE may be unable to produce images of satisfactory quality. Recently, three-dimensional (3-D) TEE has been introduced, which greatly improves the image quality and diagnostic value of TEE by adding an extra dimension. Further improvement could be achieved by optimizing 3-D TEE for harmonic imaging. This article describes the optimal geometry and element configuration for a matrix probe for 3-D second harmonic TEE. The array concept features separated transmit and receive subarrays. The element geometry was studied using finite element modeling and a transmit subarray prototype was examined both acoustically and with laser interferometry. The transmit subarray is suitable for its role, with a 3 MHz resonance frequency, a 40%-50% -3 dB bandwidth and crosstalk levels <-27 dB. The proposed concept for the receive subarray has a 5.6 MHz center frequency and a 50% -3 dB bandwidth. PMID:22958515
A numerical model for calculating vibration from a railway tunnel embedded in a full-space
NASA Astrophysics Data System (ADS)
Hussein, M. F. M.; Hunt, H. E. M.
2007-08-01
Vibration generated by underground railways transmits to nearby buildings causing annoyance to inhabitants and malfunctioning to sensitive equipment. Vibration can be isolated through countermeasures by reducing the stiffness of railpads, using floating-slab tracks and/or supporting buildings on springs. Modelling of vibration from underground railways has recently gained more importance on account of the need to evaluate accurately the performance of vibration countermeasures before these are implemented. This paper develops an existing model, reported by Forrest and Hunt, for calculating vibration from underground railways. The model, known as the Pipe-in-Pipe model, has been developed in this paper to account for anti-symmetrical inputs and therefore to model tangential forces at the tunnel wall. Moreover, three different arrangements of supports are considered for floating-slab tracks, one which can be used to model directly-fixed slabs. The paper also investigates the wave-guided solution of the track, the tunnel, the surrounding soil and the coupled system. It is shown that the dynamics of the track have significant effect on the results calculated in the wavenumber-frequency domain and therefore an important role on controlling vibration from underground railways.
Calculation of rotor impedance for use in design analysis of helicopter airframe vibrations
NASA Technical Reports Server (NTRS)
Nygren, Kip P.
1990-01-01
Excessive vibration is one of the most prevalent technical obstacles encountered in the development of new rotorcraft. The inability to predict these vibrations is primarily due to deficiencies in analysis and simulation tools. The Langley Rotorcraft Structural Dynamics Program was instituted in 1984 to meet long term industry needs in the area of rotorcraft vibration prediction. As a part of the Langley program, this research endeavors to develop an efficient means of coupling the rotor to the airframe for preliminary design analysis of helicopter airframe vibrations. The main effort was to modify the existing computer program for modeling the dynamic and aerodynamic behavior of rotorcraft called DYSCO (DYnamic System COupler) to calculate the rotor impedance. DYSCO was recently developed for the U.S. Army and has proven to be adaptable for the inclusion of new solution methods. The solution procedure developed to use DYSCO for the calculation of rotor impedance is presented. Verification of the procedure by comparison with a known solution for a simple wind turbine model is about 75 percent completed, and initial results are encouraging. After the wind turbine impedance is confirmed, the verification effort will continue by comparison to solutions of a more sophisticated rotorcraft model. Future work includes determination of the sensitivity of the rotorcraft airframe vibrations to helicopter flight conditions and rotor modeling assumptions. When completed, this research will ascertain the feasibility and efficiency of the impedance matching method of rotor-airframe coupling for use in the analysis of airframe vibrations during the preliminary rotorcraft design process.
Critical free vibrations of screw centrifuges and calculation of damping devices
Fainerman, I.A.
1985-05-01
In the operation of settling screw centrifuges, free vibrations may induce pulsation of the moment, which in turn triggers the protective mechanism of the reduction gear at a performance far below the theoretical one. With the aid of a diagram the author describes the construction and operation of a screw centrifuge with a damping device, and he sets forth equations whereby he can analyze the amplitude and frequency of such vibrations. He then calculates the optimum parameters of effectiveness for a damping device and establishes a sequence of calculation for the design of such a device.
Calculation of Vibrational Spectra of Coordinated Perchlorate Ion in Dipolar Aprotic Solvents
NASA Astrophysics Data System (ADS)
Mikhailov, G. P.
2014-09-01
The vibrational spectrum of perchlorate ion coordinated to Li+, Na+, and Mg2+ cations in dipolar aprotic solvents (DAS) was studied using Hartree-Fock methods not taking into account (RHF) and accounting partially for electron correlation (MP2) and B3LYP density functional theory within the polarized continuum model (PCM). Experimental and calculated spectrum-structure correlations for coordinated perchlorate-ion complexes in DAS were analyzed. It was found that the best fi t of the experimental and calculated vibrational spectra was achieved by taking into account the electron correlation and non-specific solvation.
Meier, Patrick; Oschetzki, Dominik; Rauhut, Guntram; Berger, Robert
2014-05-14
A transformation of potential energy surfaces (PES) being represented by multi-mode expansions is introduced, which allows for the calculation of anharmonic vibrational spectra of any isotopologue from a single PES. This simplifies the analysis of infrared spectra due to significant CPU-time savings. An investigation of remaining deviations due to truncations and the so-called multi-level approximation is provided. The importance of vibrational-rotational couplings for small molecules is discussed in detail. In addition, an analysis is proposed, which provides information about the quality of the transformation prior to its execution. Benchmark calculations are provided for a set of small molecules.
NASA Astrophysics Data System (ADS)
Keeli, Murat; Hirata, So; Yagi, Kiyoshi
2010-07-01
The frequencies of the infrared- and/or Raman-active (k =0) vibrations of polyethylene and polyacetylene are computed by taking account of the anharmonicity in the potential energy surfaces (PESs) and the resulting phonon-phonon couplings explicitly. The electronic part of the calculations is based on Gaussian-basis-set crystalline orbital theory at the Hartree-Fock and second-order Mller-Plesset (MP2) perturbation levels, providing one-, two-, and/or three-dimensional slices of the PES (namely, using the so-called n-mode coupling approximation with n =3), which are in turn expanded in the fourth-order Taylor series with respect to the normal coordinates. The vibrational part uses the vibrational self-consistent field, vibrational MP2, and vibrational truncated configuration-interaction (VCI) methods within the ? approximation, which amounts to including only k =0 phonons. It is shown that accounting for both electron correlation and anharmonicity is essential in achieving good agreement (the mean and maximum absolute deviations less than 50 and 90 cm-1, respectively, for polyethylene and polyacetylene) between computed and observed frequencies. The corresponding values for the calculations including only one of such effects are in excess of 120 and 300 cm-1, respectively. The VCI calculations also reproduce semiquantitatively the frequency separation and intensity ratio of the Fermi doublet involving the ?2(0) fundamental and ?8(?) first overtone in polyethylene.
NASA Astrophysics Data System (ADS)
Saleem, H.; Subashchandrabose, S.; Ramesh Babu, N.; Syed Ali Padusha, M.
2015-05-01
The FT-IR, FT-Raman and UV-Vis spectra of the Schiff base compound (E)-N?-(4-methoxybenzylidene) benzohydrazide (MBBH) have been recorded and analyzed. The optimized geometrical parameters were calculated. The complete vibrational assignments were performed on the basis of TED of the vibrational modes, calculated with the help of SQM method. NBO analysis has been carried out to explore the hyperconjugative interactions and their second order stabilization energy within the molecule. The molecular orbitals (MO's) and its energy gap were studied. The first order hyperpolarizability (?0) and related properties (?, ?0, ??) of MBBH are also calculated. All theoretical calculations were performed on the basis of B3LYP/6-311++G(d,p) level of theory.
Calculation of optical excitations in cubic semiconductors. II. Second-harmonic generation
NASA Astrophysics Data System (ADS)
Huang, Ming-Zhu; Ching, W. Y.
1993-04-01
The second-harmonic generations in 15 noncentral symmetric cubic semiconductors are systematically studied by the first-principles full band-structure method. The crystals studied are the III-V compounds AlP, AlAs, AsSb, GaP, GaAs, GaSb, InP, InAs, InSb; and the II-VI compounds ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe. Calculations are focused on the frequency-dependent complex second-order nonlinear optical susceptibilities ?(2)(?) up to 10 eV and their zero-frequency limits ?(2)(0). A simple scissor operator is applied to adjust the band gaps from the local-density calculations to the experimental values. Large numbers of k points in the sum over Brillouin zone are used which are important in resolving structures in the dispersion curves. Comparison with available experimental data on ?(2)(0) and ?(2)(?) shows general good agreement. It is shown that for a well-converged result, sufficiently high conduction-band (CB) states at least 40 eV from the top of the valence band must be included because of the large CB-CB transition-matrix elements. Correlations between the calculated nonlinear optical parameters and other physical parameters such as band-gap and static dielectric constants are also investigated. It is shown that the validity of the Miller's rule with regard to the ratio between linear and nonlinear susceptibilities is limited to the low-frequency range.
NASA Astrophysics Data System (ADS)
Kwak, Moon K.; Yang, Dong-Ho
2013-09-01
This paper is concerned with the suppression of vibrations and radiated sound of a ring-stiffened circular cylindrical shell in contact with unbounded external fluid by means of piezoelectric sensors and actuators. The dynamic model of a circular cylindrical shell based on the Sanders shell theory was considered together with a ring stiffener model. The mass and stiffness matrices for a ring stiffener were newly derived in this study and added to the mass and stiffness matrices of the cylindrical shell, respectively. The fluid-added mass matrix, which was derived by using the baffled shell theory, was also added to the mass matrix. Finally, the equations representing the piezoelectric sensor measurement and piezoelectric actuation complete the theoretical model for the addressed problem. The natural vibration characteristics of the ring-stiffened cylindrical shell both in air and in water were investigated both theoretically and experimentally. The theoretical predictions were in good agreement with the experimental results. An active vibration controller which can cope with a harmonic disturbance was designed by considering the modified higher harmonic control, which is, in fact, a band rejection filter. An active vibration control experiment on the submerged cylindrical shell was carried out in a water tank and the digital control system was used. The experimental results showed that both vibrations and radiation sound of the submerged cylindrical shell were suppressed by a pair of piezoelectric sensor and actuator.
Calculations of lattice vibrational mode lifetimes using Jazz: a Python wrapper for LAMMPS
NASA Astrophysics Data System (ADS)
Gao, Y.; Wang, H.; Daw, M. S.
2015-06-01
Jazz is a new python wrapper for LAMMPS [1], implemented to calculate the lifetimes of vibrational normal modes based on forces as calculated for any interatomic potential available in that package. The anharmonic character of the normal modes is analyzed via the Monte Carlo-based moments approximation as is described in Gao and Daw [2]. It is distributed as open-source software and can be downloaded from the website http://jazz.sourceforge.net/.
NASA Astrophysics Data System (ADS)
Song, L.; Balakrishnan, N.; Walker, K. M.; Stancil, P. C.; Thi, W. F.; Kamp, I.; van der Avoird, A.; Groenenboom, G. C.
2015-11-01
We present calculated rate coefficients for ro-vibrational transitions of CO in collisions with H atoms for a gas temperature range of 10 K ? T ? 3000 K, based on the recent three-dimensional ab initio HCO interaction potential of Song et al. Rate coefficients for ro-vibrational v=1,j=0-30\\to v\\prime =0,j\\prime transitions were obtained from scattering cross sections previously computed with the close-coupling (CC) method by Song et al. Combining these with the rate coefficients for vibrational v=1-5\\to v\\prime \\lt v quenching obtained with the infinite-order sudden approximation, we propose a new extrapolation scheme that yields the rate coefficients for ro-vibrational v=2-5,j=0-30\\to v\\prime ,j\\prime de-excitation. Cross sections and rate coefficients for ro-vibrational v=2,j=0-30\\to v\\prime =1,j\\prime transitions calculated with the CC method confirm the effectiveness of this extrapolation scheme. Our calculated and extrapolated rates are very different from those that have been adopted in the modeling of many astrophysical environments. The current work provides the most comprehensive and accurate set of ro-vibrational de-excitation rate coefficients for the astrophysical modeling of the HCO collision system. The application of the previously available and new data sets in astrophysical slab models shows that the line fluxes typically change by 20%70% in high temperature environments (800 K) with an H/H2 ratio of 1; larger changes occur for lower temperatures.
Molecular structure and vibrational spectra of dithionite ion by ab initio calculations
NASA Astrophysics Data System (ADS)
Leszczynski, Jerzy; Zerner, Michael C.
1989-07-01
The structure of the dithionite ion, S 2O 42-, is examined using quantum chemical calculations. These studies strongly suggest that only the C 2h (trans) isomer is stable in solution. The C 2v (cis) form reported in Na 2S 2O 42H 2O is stabilized by crystal forces. The calculated vibrational spectrum of the C 2h form is in excellent agreement with that observed in aqueous solution. Taking into account the negative frequency calculated for the C 2v structure yields a calculated spectrum in good agreement with that observed for the crystal.
NASA Astrophysics Data System (ADS)
Buyukmurat, Y.; Akyuz, S.
2005-06-01
The molecular geometry and molecular vibrations of 3-aminophenol and its some deuterated derivatives have been investigated with the aid of quantum chemical calculations, normal coordinate analysis using force field refinement method and vibrational spectroscopy. The barrier of the OH group pointing in the direction of the amino group with respect to the anti conformer for 3-aminophenol was computed to be 2.44 kJ/mol. The spectroscopic and theoretical results are compared to the corresponding properties for some similar molecules.
Rotational spectrum, ring-puckering vibration and ab initio calculations on tetrahydrothiophene
NASA Astrophysics Data System (ADS)
Marguls, Laurent; Eugenia Sanz, M.; Kassi, Samir; Petitprez, Denis; Wlodarczak, Georges; Lpez, Juan C.; Boggs, James E.
2001-01-01
The rotational spectra of tetrahydrothiophene, c-C 4H 8S, in the ground state (including spectra of isotopic species) and several excited vibrational states have been reinvestigated in the centimeter and the millimeter wave range up to 300 GHz. Ab initio calculations were performed for structural and conformational analysis, which confirm the experimental values. The low-lying vibrational states were analyzed within the pseudorotation description and from the pseudorotation dependence of the rotational constants the resulting potential energy function was determined.
NASA Astrophysics Data System (ADS)
Mareishi, Soraya; Kalhori, Hamed; Rafiee, Mohammad; Hosseini, Seyedeh Marzieh
2015-01-01
This paper presents an analytical solution for nonlinear free and forced vibration response of smart laminated nano-composite beams resting on nonlinear elastic foundation and under external harmonic excitation. The structure is under a temperature change and an electric excitation through the piezoelectric layers. Different distribution patterns of the single walled aligned and straight carbon nanotubes (SWCNTs) through the thickness of the beam are considered. The beam complies with Euler-Bernoulli beam theory and von Krmn geometric nonlinearity. The nonlinearity is due to the mid-plane stretching of the beam and the nonlinear stiffness of the elastic foundation. The Multiple Time Scales perturbation scheme is used to perform the nonlinear dynamical analysis of functionally graded carbon nanotube-reinforced beams. Analytical expressions of the nonlinear natural frequencies, nonlinear dynamic response and frequency response of the system in the case of primary resonance have been presented. The effects of different parameters including applied voltage, temperature change, beam geometry, the volume fraction and distribution pattern of the carbon nanotubes on the nonlinear natural frequencies and frequency-response curves are presented. It is found that the volume fractions of SWCNTs as well as their distribution pattern significantly change the behavior of the system.
Meier, Patrick; Oschetzki, Dominik; Pfeiffer, Florian; Rauhut, Guntram
2015-12-28
Resonating vibrational states cannot consistently be described by single-reference vibrational self-consistent field methods but request the use of multiconfigurational approaches. Strategies are presented to accelerate vibrational multiconfiguration self-consistent field theory and subsequent multireference configuration interaction calculations in order to allow for routine calculations at this enhanced level of theory. State-averaged vibrational complete active space self-consistent field calculations using mode-specific and state-tailored active spaces were found to be very fast and superior to state-specific calculations or calculations with a uniform active space. Benchmark calculations are presented for trans-diazene and bromoform, which show strong resonances in their vibrational spectra. PMID:26723655
Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms.
Song, Lei; Balakrishnan, N; van der Avoird, Ad; Karman, Tijs; Groenenboom, Gerrit C
2015-05-28
We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 - 30 to v' = 0, j' are calculated using the close coupling method for collision energies between 0.1 and 15,000 cm(-1) based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ? 3 to v' = 0, j' are reported for the first time at this level of theory. Also calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to H-CO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of H-CO collisions in astrophysical models. PMID:26026443
Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms
Song, Lei; Avoird, Ad van der; Karman, Tijs; Groenenboom, Gerrit C.; Balakrishnan, N.
2015-05-28
We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 ? 30 to v? = 0, j? are calculated using the close coupling method for collision energies between 0.1 and 15?000 cm{sup ?1} based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ? 3 to v? = 0, j? are reported for the first time at this level of theory. Also calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to HCO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of HCO collisions in astrophysical models.
Suresh, S; Gunasekaran, S; Srinivasan, S
2014-05-01
The solid phase FT-IR and FT-Raman spectra of 2-[2-[2-[(2,6-dichlorophenyl)amino]phenyl]acetyl] oxyacetic acid (Aceclofenac) have been recorded in the region 4000-400 and 4000-100 cm(-1) respectively. The optimized molecular geometry and fundamental vibrational frequencies are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method and a comparative study between Hartree Fork (HF) method 6-311++G(d,p) level basis set. The calculated harmonic vibrational frequencies were scaled and have been compared with experimental by obtained FT-IR and FT-Raman spectra. A detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated potential energy distribution (PED). The time dependent DFT method employed to study its absorption energy and oscillator strength. The linear polarizability (α) and the first order hyper polarizability (β) values of the investigated molecule have been computed. The electronic properties, such as HOMO and LUMO energies, molecular electrostatic potential (MESP) were also performed. Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. PMID:24556133
NASA Astrophysics Data System (ADS)
Suresh, S.; Gunasekaran, S.; Srinivasan, S.
The solid phase FT-IR and FT-Raman spectra of 2-[2-[2-[(2,6-dichlorophenyl)amino]phenyl]acetyl] oxyacetic acid (Aceclofenac) have been recorded in the region 4000-400 and 4000-100 cm-1 respectively. The optimized molecular geometry and fundamental vibrational frequencies are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method and a comparative study between Hartree Fork (HF) method 6-311++G(d,p) level basis set. The calculated harmonic vibrational frequencies were scaled and have been compared with experimental by obtained FT-IR and FT-Raman spectra. A detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated potential energy distribution (PED). The time dependent DFT method employed to study its absorption energy and oscillator strength. The linear polarizability (α) and the first order hyper polarizability (β) values of the investigated molecule have been computed. The electronic properties, such as HOMO and LUMO energies, molecular electrostatic potential (MESP) were also performed. Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis.
Xuan, Xiaopeng; Wang, Na; Xue, Zaikun
2012-10-01
In this paper, the structure of 1-carboxymethyl-3-methylimidazolium chloride was studied by X-ray diffraction, density functional theory, and FT-IR and Raman spectroscopic techniques for the first time. Title compound crystallizes in the orthorhombic space group Pca2(1) with the cell dimensions a=13.445 (6) , b=6.382 (3) , c=9.727 (5) and V=834.6 (7) (3). All the geometrical parameters have been calculated using by B3LYP with 6-311G++(d,p) basis set. Optimized geometries have been compared with the experimental data, and the hydrogen bond and short contact interactions were discussed. The vibrational frequencies, infrared intensities and Raman scattering activities of the title compound were calculated at the same level. The observed bands were assigned based on the theoretical calculations. The scaled vibrational frequencies seem to coincide with the experimental data with acceptable deviations. PMID:22728234
An Ab Initio Calculation of the Low-Frequency Vibrational Energies of the HCl Dimer
NASA Astrophysics Data System (ADS)
Gomez, P. C.; Bunker, P. R.; Karpfen, A.; Lischka, H.
1994-08-01
With the two HCl bond lengths held fixed at the monomer vibrational ground state value ( r0 = 1.284 ) we have calculated a four-dimensional ab initio potential energy surface of the HCl dimer at 400 nuclear geometries covering energies within 1000 cm -1 of the minimum. The electronic basis set is larger than that used earlier (A. Karpfen, P.R. Bunker, and P. Jensen, Chem. Phys. 149, 299-309, (1991) to obtain a surface on which dynamical calculations were carried out. We calculate the lowest 33 vibrational energies (up to 230 cm -1) involving the four large-amplitude modes on this surface using an adiabatic separation of the van der Waals stretching coordinate from the three large-amplitude bending coordinates (following S.C. Althorpe, D.C. Clary, and P. R. Bunker, Chem, Phys. Lett. 187, 345-353, (1991), and we contrast the results with those obtained using electrostatic potentials.
Novel calculation of HVDC converter harmonics by linearization in the time-domain
Perkins, B.K.; Iravani, M.R.
1997-04-01
There is an increasing interest in the steady-state analysis of high power converter circuits for the computation of both characteristic and uncharacteristic harmonics. Uncharacteristic harmonics arise due to asymmetries in excitation/operation and are of particular interest given their overall adverse effect on the power system. Frequency domain methods for harmonic analysis are efficient though not necessarily comprehensive; that is not all the necessary details of the system are simultaneously modeled. This paper presents a novel technique that is both efficient and comprehensive as the time domain nature of the differential/algebraic equations describing the converter operation is retained. Efficient convergence of the time domain boundary value problem is assured by an appropriate linearization. Subsequent Fourier analysis of the time domain solution yields the harmonic spectra. Comparison is made with time domain steady-state solutions obtained by brute-force computation.
Morita, Masato; Takahashi, Kaito
2013-09-28
Multidimensional local mode calculations are performed for OH stretching vibrations of the gas phase OH(-)(H2O)2 and OH(-)(H2O)2Ar clusters in the 1000-4000 cm(-1) energy range. The potential energies and the associated dipole moment values are calculated with MP2/6-311++G(3df,3pd). To fully take into account the anharmonic effects for the stretching vibrations of the ionic hydrogen bonded OHs (IHB OHs), those donating H to the O atom in OH(-), the vibrational Hamiltonian represented by the discrete variable representation (DVR) technique is diagonalized without using any truncation/contraction scheme for the basis. The necessary potential energies and dipole moment values at the DVR grid points are supplied by the polynomial inter- and extrapolations based on the values calculated at fine spatial grid points. We found that the peaks at 2700 cm(-1) should be assigned to the first overtone (?: 0 ? 2) of the IHB OH stretching vibrations rather than the previous assignment of the fundamental of the IHB OH based on harmonic frequencies. The relevant fundamental peaks should be observed around 1600-2000 cm(-1) where no experimental observation has been performed. This prediction of the fundamental peak positions leads to a simple correlation between the magnitude of the red-shift of the IHB OH stretching vibrational peak position and the cluster size of OH(-)(H2O)n for n = 1-3. Furthermore, to determine important contributions toward the assignment of the experimental spectrum, detailed analyses are performed from the following 3 viewpoints: (1) mode coupling between the inter water IHB OH stretching vibrations, (2) coupling between the IHB OH and the low-frequency OO stretching vibrations and (3) argon attachment to OH(-)(H2O)2. We found that the overall shape of the vibrational spectrum can be essentially described by considering only factor (1). However, fairly large peak shifts are caused by factors (2) and (3). PMID:23912845
NASA Astrophysics Data System (ADS)
Schmidt, Matthew; Nooijen, Marcel
2011-06-01
Recent years have seen increasing interest in the structure and dynamics of molecular clusters formed when a chromophore molecule such as CO_2, OCS or N_2O is solvated by number of He atoms and/or para-H_2 molecules. A key experimental probe of their behaviour is the shift of a chromophore's vibrational transition frequency which occurs when the solvent species are attached to it. Such shifts are driven by the changes in the solvent-chromophore interaction potential upon vibrational excitation of the probe molecule. While `conventional' supermolecule calculations can often provide realistic predictions of such changes in the potential well and repulsive wall region, they become increasingly unreliable for describing the weak interactions at long range where most of the solvent species in a large cluster are located. It is therefore important to have accurate relative-orientation and monomer-stretching dependent long-range C_6, C_8 and C10 dispersion coefficients to incorporate into the models for the interaction potential and for its dependence on the chromophore's vibrational state. This paper describes how those coefficients can be obtained from calculated monomer dipole, quadrupole, and octupole polarizabilities for imaginary frequencies, and by making use of the Casimir-Polder relation and angular momentum coupling to extract orientation-dependent quantities. The calculations are performed using a modified version of the ACES2 program system which allows the calculation of dipole, quadrupole and octupole polarizabilities at the EOM-CCSD level, and of static multipole moments using CCSD(T) calculations and adequate basis sets. For each relevant level of the chromophore, vibrational averaging is performed by calculating the imaginary frequency polarizabilities at judiciously chosen geometries and performing a numerical integration using the free-molecule vibrational wavefunction. Subsequent work will involve merging this long-range part of the potential with a short-range part obtained from 'conventional' CCSD(T) calculations and using it in PIMC simulations of cluster behaviour. H. Li, N. Blinov, P.-N. Roy and R.J. Le Roy, J. Chem. Phys. 130, 144305 (2009).
Shin, Hee Won; Ocola, Esther J.; Kim, Sunghwan; Laane, Jaan
2014-01-01
The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S1(?,?*) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S0 and S1(?,?*) electronic states. In each case the decreased ? bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S0 and S1(?,?*) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S1(?,?*) excited state. PMID:25669377
Shin, Hee Won; Ocola, Esther J.; Laane, Jaan; Kim, Sunghwan
2014-01-21
The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S{sub 1}(π,π{sup *}) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S{sub 0} and S{sub 1}(π,π{sup *}) electronic states. In each case the decreased π bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S{sub 0} and S{sub 1}(π,π{sup *}) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S{sub 1}(π,π{sup *}) excited state.
Fornaro, Teresa; Biczysko, Malgorzata; Monti, Susanna; Barone, Vincenzo
2014-06-01
Computational spectroscopy techniques have become in the last few years an effective means to analyze and assign infrared (IR) spectra of molecular systems of increasing dimensions and in different environments. However, transition from compilation of harmonic data to fully anharmonic simulations of spectra is still underway. The most promising results for large systems have been obtained, in our opinion, by perturbative vibrational approaches based on potential energy surfaces computed by hybrid (especially B3LYP) density functionals and medium size (e.g. SNSD) basis sets. In this framework, we are actively developing a comprehensive and robust computational protocol aimed at quantitative reproduction of the spectra of nucleic acid base complexes and their adsorption on solid supports (organic/inorganic). In this contribution we report the essential results of the first step devoted to isolated monomers and dimers. It is well known that in order to model the vibrational spectra of weakly bound molecular complexes dispersion interactions should be taken into proper account. In this work we have chosen two popular and inexpensive approaches to model dispersion interactions, namely the semi-empirical dispersion correction (D3) and pseudopotential based (DCP) methodologies both in conjunction with the B3LYP functional. These have been used for simulating fully anharmonic IR spectra of nucleobases and their dimers through generalized second order vibrational perturbation theory (GVPT2). We have studied, in particular, isolated adenine, hypoxanthine, uracil, thymine and cytosine, the hydrogen-bonded and stacked adenine and uracil dimers, and the stacked adenine-naphthalene heterodimer. Anharmonic frequencies are compared with standard B3LYP results and experimental findings, while the computed interaction energies and structures of complexes are compared to the best available theoretical estimates. PMID:24531740
Fornaro, Teresa; Biczysko, Malgorzata; Monti, Susanna; Barone, Vincenzo
2015-01-01
Computational spectroscopy techniques have become in the last years effective means to analyze and assign infrared (IR) spectra for molecular systems of increasing dimensions and in different environments. However, transition from compilations of harmonic data to full anharmonic simulations of spectra is still under way. The most promising results for large systems have been obtained, in our opinion, by perturbative vibrational approaches based on potential energy surfaces computed by hybrid (especially B3LYP) density functionals and medium size (e.g. SNSD) basis sets. In this framework, we are actively developing a comprehensive and robust computational protocol aimed to a quantitative reproduction of the spectra of nucleic acid bases complexes and their adsorption on solid supports (organic/inorganic). In this contribution we report the essential results of the first step devoted to isolated monomers and dimers. It is well known that in order to model the vibrational spectra of weakly bound molecular complexes dispersion interactions should be taken into proper account. In this work, we have chosen two popular and inexpensive approaches to model dispersion interaction, namely the semi-empirical dispersion correction (D3) and pseudopotential based (DCP) methodologies both in conjunction with the B3LYP functional. These have been used for simulating fully anharmonic IR spectra of nucleobases and their dimers through generalized second order vibrational perturbation theory (GVPT2). We have studied, in particular, isolated adenine, hypoxanthine, uracil, thymine and cytosine, the hydrogen-bonded and stacked adenine and uracil dimers, and the stacked adenine-naphthalene heterodimer. Anharmonic frequencies are compared with standard B3LYP results and experimental findings, while the computed interaction energies and structures of complexes are compared to the best available theoretical estimates. PMID:24531740
A simplified spherical harmonic method for coupled electron-photon transport calculations
Josef, J.A.
1996-12-01
In this thesis we have developed a simplified spherical harmonic method (SP{sub N} method) and associated efficient solution techniques for 2-D multigroup electron-photon transport calculations. The SP{sub N} method has never before been applied to charged-particle transport. We have performed a first time Fourier analysis of the source iteration scheme and the P{sub 1} diffusion synthetic acceleration (DSA) scheme applied to the 2-D SP{sub N} equations. Our theoretical analyses indicate that the source iteration and P{sub 1} DSA schemes are as effective for the 2-D SP{sub N} equations as for the 1-D S{sub N} equations. Previous analyses have indicated that the P{sub 1} DSA scheme is unstable (with sufficiently forward-peaked scattering and sufficiently small absorption) for the 2-D S{sub N} equations, yet is very effective for the 1-D S{sub N} equations. In addition, we have applied an angular multigrid acceleration scheme, and computationally demonstrated that it performs as well for the 2-D SP{sub N} equations as for the 1-D S{sub N} equations. It has previously been shown for 1-D S{sub N} calculations that this scheme is much more effective than the DSA scheme when scattering is highly forward-peaked. We have investigated the applicability of the SP{sub N} approximation to two different physical classes of problems: satellite electronics shielding from geomagnetically trapped electrons, and electron beam problems. In the space shielding study, the SP{sub N} method produced solutions that are accurate within 10% of the benchmark Monte Carlo solutions, and often orders of magnitude faster than Monte Carlo. We have successfully modeled quasi-void problems and have obtained excellent agreement with Monte Carlo. We have observed that the SP{sub N} method appears to be too diffusive an approximation for beam problems. This result, however, is in agreement with theoretical expectations.
Nagabalasubramanian, P B; Periandy, S; Karabacak, Mehmet; Govindarajan, M
2015-06-15
The solid phase FT-IR and FT-Raman spectra of 4-vinylcyclohexene (abbreviated as 4-VCH) have been recorded in the region 4000-100cm(-1). The optimized molecular geometry and vibrational frequencies of the fundamental modes of 4-VCH have been precisely assigned and analyzed with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method at 6-311++G(d,p) level basis set. The theoretical frequencies were properly scaled and compared with experimentally obtained FT-IR and FT-Raman spectra. Also, the effect due the substitution of vinyl group on the ring vibrational frequencies was analyzed and a detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated total energy distribution (TED). The time dependent DFT (TD-DFT) method was employed to predict its electronic properties, such as electronic transitions by UV-Visible analysis, HOMO and LUMO energies, molecular electrostatic potential (MEP) and various global reactivity and selectivity descriptors (chemical hardness, chemical potential, softness, electrophilicity index). Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Atomic charges obtained by Mulliken population analysis and NBO analysis are compared. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures are also calculated. PMID:25795608
Accurate quantum dynamics calculations of vibrational spectrum of dideuteromethane CH2D2.
Yu, Hua-Gen
2015-05-21
We report a rigorous variational study of the infrared (IR) vibrational spectra of both CH2D2 and (13)CH2D2 isotopomers using an exact molecular Hamiltonian. Calculations are carried out using a recently developed multi-layer Lanczos algorithm based on the accurate refined Wang and Carrington potential energy surface of methane and the low-order truncated ab initio dipole moment surface of Yurchenko et al. [J. Mol. Spectrosc. 291, 69 (2013)]. All well converged 357 vibrational energy levels up to 6100 cm(-1) of CH2D2 are obtained, together with a comparison to previous calculations and 91 experimental bands available. The calculated frequencies are in excellent agreement with the experimental results and give a root-mean-square error of 0.67?cm(-1). In particular, we also compute the transition intensities from the vibrational ground state for both isotopomers. Based on the theoretical results, 20 experimental bands are suggested to be re-assigned. Surprisingly, an anomalous C isotopic effect is discovered in the n?5 modes of CH2D2. The predicted IR spectra provide useful information for understanding those unknown bands. PMID:26001461
NASA Astrophysics Data System (ADS)
Nagabalasubramanian, P. B.; Periandy, S.; Karabacak, Mehmet; Govindarajan, M.
2015-06-01
The solid phase FT-IR and FT-Raman spectra of 4-vinylcyclohexene (abbreviated as 4-VCH) have been recorded in the region 4000-100 cm-1. The optimized molecular geometry and vibrational frequencies of the fundamental modes of 4-VCH have been precisely assigned and analyzed with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method at 6-311++G(d,p) level basis set. The theoretical frequencies were properly scaled and compared with experimentally obtained FT-IR and FT-Raman spectra. Also, the effect due the substitution of vinyl group on the ring vibrational frequencies was analyzed and a detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated total energy distribution (TED). The time dependent DFT (TD-DFT) method was employed to predict its electronic properties, such as electronic transitions by UV-Visible analysis, HOMO and LUMO energies, molecular electrostatic potential (MEP) and various global reactivity and selectivity descriptors (chemical hardness, chemical potential, softness, electrophilicity index). Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Atomic charges obtained by Mulliken population analysis and NBO analysis are compared. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures are also calculated.
Dai, Peng; Jiang, Nan; Tan, Ren-Xiang
2016-01-01
Elucidation of absolute configuration of chiral molecules including structurally complex natural products remains a challenging problem in organic chemistry. A reliable method for assigning the absolute stereostructure is to combine the experimental circular dichroism (CD) techniques such as electronic and vibrational CD (ECD and VCD), with quantum mechanics (QM) ECD and VCD calculations. The traditional QM methods as well as their continuing developments make them more applicable with accuracy. Taking some chiral natural products with diverse conformations as examples, this review describes the basic concepts and new developments of QM approaches for ECD and VCD calculations in solution and solid states. PMID:26880597
Vibrationally resolved photoelectron imaging of Cu2H- and AgCuH- and theoretical calculations.
Xie, Hua; Li, Xiaoyi; Zhao, Lijuan; Liu, Zhiling; Qin, Zhengbo; Wu, Xia; Tang, Zichao; Xing, Xiaopeng
2013-02-28
Vibrationally resolved photoelectron spectra have been obtained for Cu(2)H(-) and AgCuH(-) using photoelectron imaging at 355 nm. Two transition bands X and A are observed for each spectrum. The X bands in both spectra show the vibration progressions of the Cu-H stretching mode and the broad peaks of these progressions indicate significant structural changes from Cu(2)H(-) and AgCuH(-) to their neutral ground states. The A bands in the spectra of Cu(2)H(-) and CuAgH(-) show stretching progressions of Cu-Cu and Ag-Cu, respectively. The contours of these two progressions are pretty narrow, indicating relatively small structural changes from Cu(2)H(-) and AgCuH(-) to their neutral excited states. Calculations based on density functional theory indicate that the ground states of Cu(2)H(-) and AgCuH(-) and the first excited states of their neutrals are linear, whereas their neutral ground states are bent. The photoelectron detachment energies and vibrational frequencies from these calculations are in good agreement with the experimental observations. Especially, the theoretical predication of linear structures for the anions and the neutral excited states are supported by the spectral features of A bands, in which the bending modes are inactive. Comparisons among the vertical detachment energies of Cu(2)H(-), AgCuH(-), and their analogs help to elucidate electronic characteristics of coinage metal elements and hydrogen in small clusters. PMID:23388039
Joseph, Lynnette; Sajan, D; Reshmy, R; Arun Sasi, B S; Erdogdu, Y; Thomas, K Kurien
2012-12-01
The powder form NIR-FT Raman and FT-IR spectra of 3-acetyl-7-methoxycoumarin (3A7MC) have been recorded in the regions 4000-400 and 3500-100 cm(-1), respectively. The equilibrium geometry, vibrational frequencies, band intensities, NMR spectra, NBO analysis and UV-Vis spectral studies of the most stable conformer have been calculated by density functional B3LYP method with the 6-311G(d,p) basis set. A complete vibrational analysis has been attempted on the basis of experimental infrared and Raman spectra, the calculated wavenumber and intensity of the vibrational bands and the potential energy distribution over the internal coordinates. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping the electron density isosurface with electrostatic potential surfaces (ESP). Natural bond orbital analysis has been carried out to understand the nature of different interactions responsible for the electron delocalization and the intramolecular charge transfer between the orbitals (n??(?), n??(?), ???(?)). PMID:23078790
NASA Astrophysics Data System (ADS)
Ladetto, Mara F.; Mrquez, Mara B.; Brandn, Silvia A.
2014-10-01
In this work, we have presented a structural and vibrational study on the properties in gas and aqueous solution phases of oxcarbazepine, a polymorphic anticonvulsant substance, combining the available IR and Raman spectra with Density Functional Theory (DFT) calculations. Two stable C1 and C2 forms for the title molecule were theoretically determined by using the hybrid B3LYP/6-31G* method. The integral equation formalism variant polarised continuum model (IEFPCM) was employed to study the solvent effects by means of the self-consistent reaction field (SCRF) method. The vibrational spectra for the two forms of oxcarbazepine were completely assigned together with two dimeric species also observed in the solid phase. The presences of the two C1 and C2 forms together with the two dimeric species are supported by the IR and Raman bands between 1424 and 125 cm-1. Here, the properties for both forms of oxcarbazepine are compared and discussed.
NASA Astrophysics Data System (ADS)
Scribano, Yohann; Benoit, David M.
2008-06-01
We adapt a variation-perturbation method to perform vibrational configuration interaction (VCI) calculations on large molecular systems. Starting from a self-consistent vibrational wave function, we use the vibrational configuration interaction with perturbation selected interactions (VCIPSI) algorithm to select an active VCI space iteratively. We then extend this approach to use a reduced-coupling description of potential energy surfaces. The accuracy of the method is tested on methane and benzoic acid molecules. The significant reduction in the size of the VCI basis obtained using the VCIPSI scheme does not affect the quality of the computed vibrational frequencies and reduces computational time dramatically.
NASA Astrophysics Data System (ADS)
Lamichhane, Hari; Hastings, Gary
2009-11-01
Density functional theory (DFT) based vibrational frequency calculations of Fe4S4(SR)4^n- clusters show that the intense iron-sulfur stretching modes lie in the frequency region between 300-400 cm-1. Among them the iron-sulfur ligand (Fe-S^t) stretching modes are more intense and ˜ 30 cm-1 lower in frequency than the iron-sulfur body (Fe-S^b) stretching modes. Calculations in tetrahydrofuran (THF) show that all these iron-sulfur stretching modes of vibration downshift by ˜ 20 cm-1 upon reduction of the molecule. On the other hand, we have not observed any intense bands from chlorophyll a in the frequency region 400 to 320 cm-1 from the calculations. In an attempt to detect modes associated with iron sulfur clusters in PS I we have obtained light induced (P700^+ - P700) FTIR difference spectra for PSI particles from S. 6803 in the far infrared region. We observe difference bands at many frequencies in the 600-300 cm-1 region. Based on our calculations and literature values we claim that the negative bands at 388 cm-1 and 353 cm-1 in the (P700^+ - P700) FTIR difference spectra be assigned to Fe-S^b and Fe-S^t stretching modes of the ground state of the iron-sulfur cluster FB.
NASA Technical Reports Server (NTRS)
Chaban, Galina M.; Gerber, R. Benny; Kwak, Dochan (Technical Monitor)
2001-01-01
Anharmonic vibrational frequencies and intensities are computed for hydrogen fluoride clusters (HF)n with n=3,4 and mixed clusters of hydrogen fluoride with water (HF)n(H2O)n where n=1,2. For the (HF)4(H2O)4 complex, the vibrational spectra are calculated at the harmonic level, and anharmonic effects are estimated. Potential energy surfaces for these systems are obtained at the MP2/TZP level of electronic structure theory. Vibrational states are calculated from the potential surface points using the correlation-corrected vibrational self-consistent field (CC-VSCF) method. The method accounts for the anharmonicities and couplings between all vibrational modes and provides fairly accurate anharmonic vibrational spectra that can be directly compared with experimental results without a need for empirical scaling. For (HF)n, good agreement is found with experimental data. This agreement shows that the MP2 potential surfaces for these systems are reasonably reliable. The accuracy is best for the stiff intramolecular modes, which indicates the validity of MP2 in describing coupling between intramolecular and intermolecular degrees of freedom. For (HF)n(H2O)n experimental results are unavailable. The computed intramolecular frequencies show a strong dependence on cluster size. Intensity features are predicted for future experiments.
NASA Technical Reports Server (NTRS)
Chaban, Galina M.; Gerber, R. Benny
2002-01-01
Anharmonic vibrational frequencies and intensities are computed for hydrogen fluoride clusters (HF)n, with n = 3, 4 and mixed clusters of hydrogen fluoride with water (HF)n(H2O)n where n = 1, 2. For the (HF)4(H2O)4 complex, the vibrational spectra are calculated at the harmonic level, and anharmonic effects are estimated. Potential energy surfaces for these systems are obtained at the MP2/TZP level of electronic structure theory. Vibrational states are calculated from the potential surface points using the correlation-corrected vibrational self-consistent field method. The method accounts for the anharmonicities and couplings between all vibrational modes and provides fairly accurate anharmonic vibrational spectra that can be directly compared with experimental results without a need for empirical scaling. For (HF)n, good agreement is found with experimental data. This agreement shows that the Moller-Plesset (MP2) potential surfaces for these systems are reasonably reliable. The accuracy is best for the stiff intramolecular modes, which indicates the validity of MP2 in describing coupling between intramolecular and intermolecular degrees of freedom. For (HF)n(H2O)n experimental results are unavailable. The computed intramolecular frequencies show a strong dependence on cluster size. Intensity features are predicted for future experiments.
NASA Technical Reports Server (NTRS)
Gregurick, Susan K.; Chaban, Galina M.; Gerber, R. Benny; Kwak, Dochou (Technical Monitor)
2001-01-01
The second-order Moller-Plesset ab initio electronic structure method is used to compute points for the anharmonic mode-coupled potential energy surface of N-methylacetamide (NMA) in the trans(sub ct) configuration, including all degrees of freedom. The vibrational states and the spectroscopy are directly computed from this potential surface using the Correlation Corrected Vibrational Self-Consistent Field (CC-VSCF) method. The results are compared with CC-VSCF calculations using both the standard and improved empirical Amber-like force fields and available low temperature experimental matrix data. Analysis of our calculated spectroscopic results show that: (1) The excellent agreement between the ab initio CC-VSCF calculated frequencies and the experimental data suggest that the computed anharmonic potentials for N-methylacetamide are of a very high quality; (2) For most transitions, the vibrational frequencies obtained from the ab initio CC-VSCF method are superior to those obtained using the empirical CC-VSCF methods, when compared with experimental data. However, the improved empirical force field yields better agreement with the experimental frequencies as compared with a standard AMBER-type force field; (3) The empirical force field in particular overestimates anharmonic couplings for the amide-2 mode, the methyl asymmetric bending modes, the out-of-plane methyl bending modes, and the methyl distortions; (4) Disagreement between the ab initio and empirical anharmonic couplings is greater than the disagreement between the frequencies, and thus the anharmonic part of the empirical potential seems to be less accurate than the harmonic contribution;and (5) Both the empirical and ab initio CC-VSCF calculations predict a negligible anharmonic coupling between the amide-1 and other internal modes. The implication of this is that the intramolecular energy flow between the amide-1 and the other internal modes may be smaller than anticipated. These results may have important implications for the anharmonic force fields of peptides, for which N-methylacetamide is a model.
NASA Astrophysics Data System (ADS)
Mishra, Rashmi; Srivastava, Anubha; Sharma, Anamika; Tandon, Poonam; Baraldi, Cecilia; Gamberini, Maria Christina
2013-01-01
The global problem of advancing bacterial resistance to newer drugs has led to renewed interest in the use of Chloramphenicol Palmitate (C27H42Cl2N2O6) [Palmitic acid alpha ester with D-threo-(-),2-dichloro-N-(beta-hydroxy-alpha-(hydroxymethyl)-p-nitrophenethyl)acetamide also known as Detereopal]. The characterization of the three polymorphic forms of Chloramphenicol Palmitate (CPP) was done spectroscopically by employing FT-IR and FT-Raman techniques. The equilibrium geometry, various bonding features, and harmonic wavenumbers have been investigated for most stable form A with the help of DFT calculations and a good correlation was found between experimental data and theoretical values. Electronic properties have been analyzed employing TD-DFT for both gaseous and solvent phase. The theoretical calculation of thermodynamical properties along with NBO analysis has also been performed to have a deep insight into the molecule for further applications.
Gravitational Harmonics from Shallow Resonant Orbits. [GEOS 2 satellite - orbit calculation
NASA Technical Reports Server (NTRS)
Wagner, C. A.; Klosko, S. M.
1975-01-01
Five gravitational constraints were derived for the GEOS 2 orbit (order 13, to 30th degree) whose principal resonant period is 6 days. The constraints explain the sinusoidal variation with argument of perigee of a lumped harmonic found from 41 6-day arcs of optical and laser data. The condition equations, derived from elementary perturbation theory are shown to account for almost all of the resonant information in the tracking data.
NASA Astrophysics Data System (ADS)
Pirmohammadi, A. A.; Pourseifi, M.; Rahmani, O.; Hoseini, S. A. H.
2014-07-01
This paper investigates active vibration suppression of a single-walled carbon nanotube (SWCNT) under the action of a moving harmonic load using Eringen's nonlocal elasticity theory. The SWCNT is modeled according to the nonlocal Euler-Bernoulli beam theory. A Dirac-delta function is used to describe the position of the moving load along the SWCNT. Next, a linear classical optimal control algorithm with displacement-velocity feedback is used to suppress vibration in the SWCNT with control forces acting as actuators. The effects of a small-scale parameter, slenderness ratio, moving load velocity, and the excitation frequency of a moving load on the dynamic deflection of the SWCNT are examined. Finally, the ability of the control algorithm to suppress the response of the SWCNT under the effects of a moving load with a number of controlled modes and control forces is surveyed.
NASA Astrophysics Data System (ADS)
Stanke, Monika; Adamowicz, Ludwik
2014-10-01
We report very accurate calculations of the complete pure vibrational spectrum of the T2 molecule with an approach where the Born-Oppenheimer (BO) approximation is not assumed. As the considered states correspond to the zero total angular momentum, their non-BO wave functions are spherically symmetric and are expanded in terms of all-particle, one-center, spherically symmetric explicitly correlated Gaussian functions multiplied by even nonnegative powers of the internuclear distance. The nonrelativistic energies of the states obtained in the non-BO calculations are corrected for the relativistic effects of the order of ?2 (where ? is the fine structure constant) calculated as expectation values of the operators representing these effects.
A three-dimensional tunnel model for calculation of train-induced ground vibration
NASA Astrophysics Data System (ADS)
Forrest, J. A.; Hunt, H. E. M.
2006-07-01
The frequency range of interest for ground vibration from underground urban railways is approximately 20 to 100 Hz. For typical soils, the wavelengths of ground vibration in this frequency range are of the order of the spacing of train axles, the tunnel diameter and the distance from the tunnel to nearby building foundations. For accurate modelling, the interactions between these entities therefore have to be taken into account. This paper describes an analytical three-dimensional model for the dynamics of a deep underground railway tunnel of circular cross-section. The tunnel is conceptualised as an infinitely long, thin cylindrical shell surrounded by soil of infinite radial extent. The soil is modelled by means of the wave equations for an elastic continuum. The coupled problem is solved in the frequency domain by Fourier decomposition into ring modes circumferentially and a Fourier transform into the wavenumber domain longitudinally. Numerical results for the tunnel and soil responses due to a normal point load applied to the tunnel invert are presented. The tunnel model is suitable for use in combination with track models to calculate the ground vibration due to excitation by running trains and to evaluate different track configurations.
NASA Astrophysics Data System (ADS)
Carney, G. D.; Adler-Golden, S. M.; Lesseski, D. C.
1986-04-01
This paper reports (1) improved values for low-lying vibration intervals of H3(+), H2D(+), D2H(+), and D3(+) calculated using the variational method and Simons-Parr-Finlan (1973) representations of the Carney-Porter (1976) and Dykstra-Swope (1979) ab initio H3(+) potential energy surfaces, (2) quartic normal coordinate force fields for isotopic H3(+) molecules, (3) comparisons of variational and second-order perturbation theory, and (4) convergence properties of the Lai-Hagstrom internal coordinate vibrational Hamiltonian. Standard deviations between experimental and ab initio fundamental vibration intervals of H3(+), H2D(+), D2H(+), and D3(+) for these potential surfaces are 6.9 (Carney-Porter) and 1.2/cm (Dykstra-Swope). The standard deviations between perturbation theory and exact variational fundamentals are 5 and 10/cm for the respective surfaces. The internal coordinate Hamiltonian is found to be less efficient than the previously employed 't' coordinate Hamiltonian for these molecules, except in the case of H2D(+).
Selective calculation of high-intensity vibrations in molecular resonance Raman spectra
NASA Astrophysics Data System (ADS)
Kiewisch, Karin; Neugebauer, Johannes; Reiher, Markus
2008-11-01
We present an intensity-driven approach for the selective calculation of vibrational modes in molecular resonance Raman spectra. The method exploits the ideas of the mode-tracking algorithm [M. Reiher and J. Neugebauer, J. Chem. Phys. 118, 1634 (2003)] for the calculation of preselected molecular vibrations and of Heller's gradient approximation [Heller et al., J. Phys. Chem. 86, 1822 (1982)] for the estimation of resonance Raman intensities. The gradient approximation allows us to construct a basis vector for the subspace iteration carried out in the mode-tracking calculation, which corresponds to an artificial collective motion of the molecule that contains the entire intensity in the resonance Raman spectrum. Subsequently, the algorithm generates new basis vectors from which normal mode approximations are obtained. It is then possible to provide estimates for (i) the accuracy of the normal mode approximations and (ii) the intensity of these modes in the final resonance Raman spectrum. This approach is tested for the examples of uracil and a structural motif from the E colicin binding immunity protein Im7, in which a few aromatic amino acids dominate the resonance Raman spectrum at wavelengths larger than 240 nm.
Accurate variational calculations and analysis of the HOCl vibrational energy spectrum
Skokov, S.; Qi, J.; Bowman, J.M.; Yang, C.; Gray, S.K.; Peterson, K.A.; Mandelshtam, V.A.
1998-12-01
Large scale variational calculations for the vibrational states of HOCl are performed using a recently developed, accurate {ital ab initio} potential energy surface. Three different approaches for obtaining vibrational states are employed and contrasted; a truncation/recoupling scheme with direct diagonalization, the Lanczos method, and Chebyshev iteration with filter diagonalization. The complete spectrum of bound states for nonrotating HOCl is computed and analyzed within a random matrix theory framework. This analysis indicates almost entirely regular dynamics with only a small degree of chaos. The nearly regular spectral structure allows us to make assignments for the most significant part of the spectrum, based on analysis of coordinate expectation values and eigenfunctions. Ground state dipole moments and dipole transition probabilities are also calculated using accurate {ital ab initio} data. Computed values are in good agreement with available experimental data. Some exact rovibrational calculations for J=1, including Coriolis coupling, are performed. The exact results are nearly identical with those obtained from the adiabatic rotation approximation and very close to those from the centrifugal sudden approximation, thus indicating a very small degree of asymmetry and Coriolis coupling for the HOCl molecule. {copyright} {ital 1998 American Institute of Physics.}
Calculation of low-frequency vibrational modes of biologically important isomers
NASA Astrophysics Data System (ADS)
Jones, Inke; Rainsford, Tamath J.; Fischer, Bernd M.; Abbott, Derek
2007-12-01
In this paper we compare the value of different molecular modeling techniques for the prediction of vibrational modes, especially in the mid- and far-infrared region. There is a wide range of different levels of theory available for molecular modelling - the choice depending on the kind of system to be investigated. For our calculations we use different theoretical approaches such as Hartree-Fock and Density functional theory. We also compare the performances of two available electronic structure programs-Gamess-US and Gaussian03. As examples, we use two different retinoids - all-trans retinal and all-trans retinoic acid - derivatives of Vitamin A.
Using symmetry-adapted optimized sum-of-products basis functions to calculate vibrational spectra
NASA Astrophysics Data System (ADS)
Leclerc, Arnaud; Carrington, Tucker
2016-01-01
Vibrational spectra can be computed without storing full-dimensional vectors by using low-rank sum-of-products (SOP) basis functions. We introduce symmetry constraints in the SOP basis functions to make it possible to separately calculate states in different symmetry subgroups. This is done using a power method to compute eigenvalues and an alternating least squares method to optimize basis functions. Owing to the fact that the power method favours the convergence of the lowest states, one must be careful not to exclude basis functions of some symmetries. Exploiting symmetry facilitates making assignments and improves the accuracy. The method is applied to the acetonitrile molecule.
Krishnakumar, V; Prabavathi, N
2009-05-01
This work deals with the vibrational spectroscopy of 1-chloro-2,4-dinitrobenzene (CDNB) by means of quantum chemical calculations. The FTIR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6-311+G** basis set combinations, and was scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled quantum mechanical force field. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound, which showed excellent agreement with the observed spectra. PMID:19124269
NASA Astrophysics Data System (ADS)
Arivazhagan, M.; Manivel, S.; Jeyavijayan, S.; Meenakshi, R.
2015-01-01
The FTIR and FT-Raman spectra of 2-ethylimidazole (2EIDZ) have been recorded in the region 4000-400 cm-1 and 3500-50 cm-1, respectively. Utilizing the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. The optimized molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, were calculated by ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) methods with 6-311++G(d,p) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared and Raman spectra of 2EIDZ is also reported based on total energy distribution (TED). The values of the total dipole moment (?) and the first-order hyperpolarizability (?) of the compound were computed. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. Besides, HOMO and LUMO analysis, Mulliken's charge analysis and several thermodynamic properties have been calculated.
NASA Astrophysics Data System (ADS)
Cui, Qiang; Karplus, Martin
2000-01-01
Analytical second derivatives for combined QM/MM calculations have been formulated and implemented in the CHARMM program interfaced with the ab initio quantum mechanical GAMESS and CADPAC programs. This makes possible evaluation of vibrational frequencies and infrared intensities in large systems that cannot be treated effectively by QM or MM alone; examples are polarizable molecules in solution and substrates or transition states in enzymes. Test calculations on a number of systems, including formamide in water, butanol, a model transition state structure for triosephosphate isomerase and the active site model of myoglobin, show that the MM description of the environment can capture much of its polarization effects on the QM region. Thus the implementation of analytical second derivatives within the QM/MM framework has considerable potential for the study of large systems.
Castillo, Mara V; Pergomet, Jorgelina L; Carnavale, Gustavo A; Davies, Lilian; Zinczuk, Juan; Brandn, Silvia A
2015-01-01
In this study 3,3',4,4'-tetrachloroazobenzene (TCAB) was prepared and then characterized by infrared, Raman, multidimensional nuclear magnetic resonance (NMR) and ultraviolet-visible spectroscopies. The density functional theory (DFT) together with the 6-31G(*) and 6-311++G(**) basis sets were used to study the structures and vibrational properties of the two cis and trans isomers of TCAB. The harmonic vibrational wavenumbers for the optimized geometries were calculated at the same theory levels. A complete assignment of all the observed bands in the vibrational spectra of TCAB was performed combining the DFT calculations with the scaled quantum mechanical force field (SQMFF) methodology. The molecular electrostatic potentials, atomic charges, bond orders and frontier orbitals for the two isomers of TCAB were compared and analyzed. The comparison of the theoretical ultraviolet-visible spectrum with the corresponding experimental demonstrates a good concordance while the calculated (1)H and (13)C chemicals shifts are in good conformity with the corresponding experimental NMR spectra of TCAB in solution. The npp(*) transitions for both forms were studied by natural bond orbital (NBO) while the topological properties were calculated by employing Bader's Atoms in the Molecules (AIM) theory. This study shows that the cis and trans isomers exhibit different structural and vibrational properties and absorption bands. PMID:25106816
Calculations of N 2 triplet states vibrational populations and band emissions in venusian dayglow
NASA Astrophysics Data System (ADS)
Bhardwaj, Anil; Jain, Sonal Kumar
2012-02-01
A model for N 2 triplet states band emissions in the venusian dayglow has been developed for low and high solar activity conditions. Steady state photoelectron fluxes and volume excitation rates for N 2 triplet states have been calculated using the Analytical Yield Spectra (AYS) technique. Model calculated photoelectron flux is in good agreement with Pioneer Venus Orbiter-observed electron flux. Since inter-state cascading is important for the triplet states of N 2, populations of different levels of N 2 triplet states are calculated under statistical equilibrium considering direct electron impact excitation, and cascading and quenching effects. Densities of all vibrational levels of each triplet state are calculated in the model. Height-integrated overhead intensities of N 2 triplet band emissions are calculated, the values for Vegard-Kaplan (A3?u+-X1?g+), First Positive (B3?g-A3?u+), Second Positive ( C3? u - B3? g), and Wu-Benesch ( W3? u - B3? g) bands of N 2, are 1.9 (3.2), 3 (6), 0.4 (0.8), and 0.5 (1.1) kR, respectively, for solar minimum (maximum) conditions. The intensities of the three strong Vegard-Kaplan bands (0, 5), (0, 6), and (0, 7) are 94 (160), 120 (204), and 114 (194) R, respectively, for solar minimum (maximum) conditions. Limb profiles are calculated for VK (0, 4), (0, 5), (0, 6) and (0, 7) bands. The calculated intensities on Venus are about a factor 10 higher than those on Mars. The present study provides a motivation for a search of N 2 triplet band emissions in the dayglow of Venus.
Heger, Matthias; Suhm, Martin A.; Mata, Ricardo A.
2014-09-14
The discrepancy between experimental and harmonically predicted shifts of the OH stretching fundamental of methanol upon hydrogen bonding to a second methanol unit is too large to be blamed mostly on diagonal and off-diagonal anharmonicity corrections. It is shown that a decisive contribution comes from post-MP2 electron correlation effects, which appear not to be captured by any of the popular density functionals. We also identify that the major deficiency is in the description of the donor OH bond. Together with estimates for the electronic and harmonically zero-point corrected dimer binding energies, this work provides essential constraints for a quantitative description of this simple hydrogen bond. The spectroscopic dissociation energy is predicted to be larger than 18 kJ/mol and the harmonic OH-stretching fundamental shifts by about ?121 cm{sup ?1} upon dimerization, somewhat more than in the anharmonic experiment (?111 cm{sup ?1})
Vibrations of a floating beam on marine waves
Sabaneev, Valentin S.; Tovstik, Petr E.; Tovstik, Tatiana M.; Shekhovtsov, Alexei S.
2015-03-10
Vertical vibrations of a floating pipe-concrete beam caused by a harmonic waves excitation are studied. The apparent additional mass of water, resisting force and the velocity of towing are considered. The vibration amplitude and the maximum deformations of concrete, caused by these fluctuations, are calculated.
Structural and vibrational study of primidone based on monomer and dimer calculations.
Celik, Sefa; Kecel-Gunduz, Serda; Ozel, Aysen E; Akyuz, Sevim
2015-01-01
Primidone (Mysoline), with the chemical formula 5-ethyl-5-phenyl-hexahydropyrimidine- 4,6-dione (C12H14N2O2), has been a valuable drug in the treatment of epilepsy. In the present work, the experimental IR and Raman spectra of solid phase primidone were recorded, and the results were compared with theoretical wavenumber values of monomer and dimer forms of the title molecule. Vibrational spectral simulations in the dimer form were carried out to improve the assignment of the bands in the solid phase experimental spectra. The possible stable conformers of free molecule were searched by means of torsion potential energy surfaces scan studies through two dihedral angles. The molecular geometries of the monomer and dimer forms of title molecule were optimized using DFT method at B3LYP/6-31++G(d,p) level of theory. Using PEDs determined the contributions of internal (stretching, bending, etc.) coordinates to each normal mode of vibration. Further, HOMO-LUMO energy gap and NBO properties of the investigated molecule in monomer and dimer forms were also calculated. PMID:24712318
Tetsassi Feugmo, Conrard Giresse; Ligeois, Vincent
2013-06-01
Using density functional theory, we calculate the IR and Raman signatures of the thiophenol (TP) molecule adsorbed on gold clusters by mimicking the different types of adsorption sites, and we analyze these signatures by using advanced tools implemented into the pyvib2 program. First, we follow the evolution of the vibrational normal modes from the isolated TP molecule to those of TP adsorbed on different clusters to highlight the influence of the site of adsorption on the vibrational motions. The use of the overlap matrix between the modes enables mode permutations, mode mixings, and mode splittings to be highlighted, all of which depend not only on the adsorption but also on the type of cluster and its symmetry. Second, the IR and Raman signatures were analyzed by using group coupling matrices and atomic contribution patterns based on the Hug decomposition scheme. Key results include 1) the fact that Raman spectroscopy is more sensitive than IR spectroscopy with respect to the nature of the coordination site, 2) an IR criterion that distinguishes between on-top coordination (onefold coordinated) with respect to the bridge (twofold coordinated) and hexagonal close-packed hollow site coordination (threefold coordinated), and 3) the best agreement to the experimental Raman spectrum with regard to signatures in the 500 to 1200 cm(-1) region is obtained for bridged, twofold coordination. PMID:23592337
NASA Astrophysics Data System (ADS)
Sullivan, J. F.; Heusel, H. L.; Zunic, W. M.; Durig, J. R.; Cradock, Stephen
1994-03-01
The infrared (3200-30 cm -1) and Raman (3200-10 cm -1) spectra of gaseous and solid methylisocyanate, CH 3NCO, have been recorded. Additionally, the Raman spectrum of the liquid has been obtained and qualitative depolarization ratios have been measured. The CNC bend has been observed in the far infrared and low frequency Raman spectra of the gas at approximately 172 cm -1. An additional far infrared band at ≈50 cm -1 has tentatively been assigned as the methyl torsional mode, although it could be due to the Δν = 1, Δ l = ± 1 transitions of the CNC bending mode. A complete assignment of the vibrational fundamentals is proposed. The structural parameters, force constants, and vibrational frequencies have been determined from ab initio Hartree—Fock gradient calculations using the 6-31G* basis set. Additionally, structural parameters have been obtained with the 6-311 + + G** basis set with electron correlation at the MP2 level which are compared to those obtained from the microwave data and electron diffraction study. These results are compared with the corresponding quantities obtained for similar molecules.
Ottonello, G; Zuccolini, M Vetuschi; Belmonte, D
2010-09-14
We present the results of a computational investigation with ab initio procedures of the structure-energy and vibrational properties of silica clusters in a dielectric continuum with dielectric constant ?=3.8, through density functional theory/B3LYP gas phase calculations coupled with a polarized continuum model approach [integral equation formalism applied to a polarized continuum (IEFPCM)] and those of the periodical structure D(6h) which leads to the ?-cristobalite polymorph of silica when subjected to symmetry operations with the same functional within the linear combination of atomic orbitals (LCAO) approximation and in the framework of Bloch's theorem. Based on the computed energies and vibrational features, an aggregate of the D(6h) network and the monomer locally ordered in the short-medium range and both present in the glass in a mutual arrangement lacking of spatial continuity reproduces satisfactorily the experimentally observed low T heat capacity and the deviation from the Debye T(3) law. Above T(g), the experimental heat capacity of the liquid is perfectly reproduced summing to the internal modes the translational and rotational contributions to the bulk heat capacity and subtracting the (acoustic) terms arising from coherent motion (no longer existent). PMID:20849179
NASA Astrophysics Data System (ADS)
Yu, Hua-Gen
2009-08-01
An exact variational algorithm is presented for calculating vibrational energy levels of pentaatomic molecules without any dynamical approximation. The quantum mechanical Hamiltonian of the system is expressed in a set of orthogonal coordinates defined by four scattering vectors in the body-fixed frame. The eigenvalue problem is solved using a two-layer Lanczos iterative diagonalization method in a mixed grid/basis set. A direct product potential-optimized discrete variable representation (PO-DVR) basis is used for the radial coordinates while a non-direct product finite basis representation (FBR) is employed for the angular variables. The two-layer Lanczos method requires only the actions of the Hamiltonian operator on the Lanczos vectors, where the potential-vector products are accomplished via a pseudo-spectral transform technique. By using Jacobi, Radau and orthogonal satellite vectors, we have proposed 21 types of orthogonal coordinate systems so that the algorithm is capable of describing most five-atom systems with small and/or large amplitude vibrational motions. Finally, an universal program ( PetroVib) has been developed. Its applications to the molecules CH and HO2-, and the van der Waals cluster HeCl are also discussed.
A comparison of several methods for the calculation of vibration mode shape derivatives
NASA Technical Reports Server (NTRS)
Sutter, T. R.; Camarda, C. J.; Walsh, J. L.; Adelman, H. M.
1986-01-01
Four methods for the calculation of derivatives of vibration mode shapes (eigenvectors) with respect to design parameters are reviewed and compared. These methods (finite difference method, Nelson's method, modal method and a modified modal method) are implemented in a general-purpose commercial finite element program and applied to a cantilever beam and a stiffened cylinder with a cutout. A beam tip mass, a beam root height and specific dimensions of the cylinder model comprise the design variables. Data are presented showing the amount of central processor time used to compute the first four eigenvector derivatives for each example problem; errors and rapidity of convergence of the approximate derivative to the exact derivative are taken into account. Nelson's method proved to be most reliable and efficient.
Balachandran, V; Murugan, M; Nataraj, A; Karnan, M; Ilango, G
2014-11-11
In the present study structural properties of p-cresol, and 2-methoxy-p-cresol have been studied by using B3LYP/cc-pvdz and B3PW91/cc-pvdz of Density Functional Theory (DFT) utilizing Becke three exchange functional and Lee Yang Paar correlation functional. The Fourier transform infrared and Fourier transform Raman spectra of title molecules were recorded (solid phase). Optimized geometry, harmonic vibrational frequencies and various thermodynamic parameters of the title compounds were calculated with B3LYP/cc-pvdz, and B3PW91/cc-pvdz basis sets. Non-linear optical (NLO) behavior of the p-cresol and 2-methoxy-p-cresol were investigated by determining of electric dipole moment, polarizability α, and hyperpolarizability β using the above mentioned basis sets. The molecular properties such as ionization potential, electronegativity, chemical potential, electrophilicity have been deduced from HOMO-LUMO analysis employing the same basis sets. A detailed interpretation of the infrared and Raman spectra of title molecules were reported. UV spectrum was measured in different solvent. The energy and oscillator strength are calculated by Time Dependant Density Functional Theory (TD-DFT) results. The calculated HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. The complete assignments were performed on the basis of the potential energy distribution (PED) of vibrational modes, calculated with scaled quantum mechanics (SQM) method. Finally the theoretical FT-IR, FT-Raman, and UV spectra of the title molecules have also been constructed. PMID:24892532
Ramos, J M; de M Cruz, M T; Costa, A C; Ondar, G F; Ferreira, Glaucio B; Raniero, L; Martin, A A; Versiane, O; Tllez Soto, C A
2012-11-01
The aspartateguanidoacetatenickel (II) complex, [Ni(Asp)(GAA)], was synthesized and structural analysis was performed by means of the experimental methods: determination of the C, H, N and O contents, thermogravimetry, infrared and Raman spectroscopy. DFT:B3LYP/6-311G(d, p) calculations have been performed giving optimized structure and harmonic vibrational wavenumbers. Second derivative of the FT-infrared, FT-Raman and Surface Raman Enhanced Scattering (SERS) spectra, and band deconvolution analysis were also performed. Features of the FT-infrared, FT-Raman and SERS confirmed theoretical structure prediction. Full assignment of the vibrational spectrum was also supported by a carefully analysis of the distorted geometries generated by the normal modes. The Natural Bond Orbital analysis (NBO) was also carried out as a way to study the Ni (II) hybridization leading to the pseudo planar geometry of the framework, and the extension of the atomic N and O hybrid orbital of the different amino acids in the bond formation. Bands of charge transfer and d-d transitions were assigned in the UV-Vis spectrum. PMID:22925980
Bozkaya, U?ur; Sherrill, C David
2013-08-01
Orbital-optimized coupled-electron pair theory [or simply "optimized CEPA(0)," OCEPA(0), for short] and its analytic energy gradients are presented. For variational optimization of the molecular orbitals for the OCEPA(0) method, a Lagrangian-based approach is used along with an orbital direct inversion of the iterative subspace algorithm. The cost of the method is comparable to that of CCSD [O(N(6)) scaling] for energy computations. However, for analytic gradient computations the OCEPA(0) method is only half as expensive as CCSD since there is no need to solve the ?2-amplitude equation for OCEPA(0). The performance of the OCEPA(0) method is compared with that of the canonical MP2, CEPA(0), CCSD, and CCSD(T) methods, for equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions between radicals. For bond lengths of both closed and open-shell molecules, the OCEPA(0) method improves upon CEPA(0) and CCSD by 25%-43% and 38%-53%, respectively, with Dunning's cc-pCVQZ basis set. Especially for the open-shell test set, the performance of OCEPA(0) is comparable with that of CCSD(T) (?R is 0.0003 A? on average). For harmonic vibrational frequencies of closed-shell molecules, the OCEPA(0) method again outperforms CEPA(0) and CCSD by 33%-79% and 53%-79%, respectively. For harmonic vibrational frequencies of open-shell molecules, the mean absolute error (MAE) of the OCEPA(0) method (39 cm(-1)) is fortuitously even better than that of CCSD(T) (50 cm(-1)), while the MAEs of CEPA(0) (184 cm(-1)) and CCSD (84 cm(-1)) are considerably higher. For complete basis set estimates of hydrogen transfer reaction energies, the OCEPA(0) method again exhibits a substantially better performance than CEPA(0), providing a mean absolute error of 0.7 kcal mol(-1), which is more than 6 times lower than that of CEPA(0) (4.6 kcal mol(-1)), and comparing to MP2 (7.7 kcal mol(-1)) there is a more than 10-fold reduction in errors. Whereas the MAE for the CCSD method is only 0.1 kcal mol(-1) lower than that of OCEPA(0). Overall, the present application results indicate that the OCEPA(0) method is very promising not only for challenging open-shell systems but also for closed-shell molecules. PMID:23927240
DFT Ab initio Calculation of Vibrational Frequencies in AsSe glass
NASA Astrophysics Data System (ADS)
Shrivastava, Keshav; Kassim, Hasan; Nazrul Rosli, Ahmad
2008-03-01
By using DFT double zeta wave functions, we calculated the structure, bond length (picometer, pm), frequencies(intensities)[degeneracy] for various clusters of arsenic selenide. Our results are as follows. (i) AsSe(diatomic) bond length 216pm, 244.0(1/cm). (ii) As2Se(linear) bond length 228.5 pm, frequencies 27.6(1.9) and 387.6(4.3). (iii) As2Se(triangular) As-Se 243.4 pm, As-As 223.3 pm, frequencies 237.3(2.4) and 332.4(0.05)(1/cm). (iv) As3Se (triangular) bond length 238.4 pm, frequencies 107.5 and 296(weak)(1/cm). (v) As4Se (square) bond length 250.2 pm, 58.5(0.04), 241.3(5.9)(1/cm). (vi) AsSe3 (triangular), bond length 231.2 pm, 75.9(0.003), 103.5(1.26)[2], 350.9(33.2)[2]. From this study we identify that linear As-Se-As for which the calculated frequency is 27.6(1/cm) is in agreement with the data of Nemanich, Phys. Rev. B 16, 1655(1977), J. C. Phillips et al Phys. Rev B 21, 5724(1980). We have successfully calculated several vibrational frequencies accurately which agree with the Raman data. *V. R. Devi et al J. Non-Cryst. Solids 351, 489(2005);353,111(2007)
NASA Astrophysics Data System (ADS)
Robbins, Timothy J.; Wang, Yongmei; Yao, Qi-Zheng; Wang, Zhao-Hui; Cheng, Jingcai; Li, Ying-Sing
2013-09-01
For centuries Danggui Longhui Wan has been used to treat chronic ailments, such as myelocytic leukemia. In the 1960s, the active ingredient in Danggui Longhui Wan was isolated and identified as indirubin. Indirubin has shown potent inhibition of cyclin-dependent kinase through binding to the ATP-binding site. However, indirubin shows poor solubility and low absorption, hence many derivatives have been developed to enhance these properties. One such derivative is 5?-chloro-1-isopropyl-7-azaindirubin-3?-oxime (CIADO), investigated in the current work. Infrared and Raman spectra were collected and compared with predicted spectra using density functional theory. Based on theoretical calculations, the most stable form of CIADO isomer is found to be cis (Z) and trans (E) with respect to the ring system linkage and the 3?-oxime functional group respectively. Also observed were two distinct internal rotational minima for the 1-isoprooyl group separated by a large energy barrier. The presence of two distinct isopropyl conformations observed in our calculations was confirmed with temperature-dependent IR experiments. Assignment of experimental vibrational modes was carried out based on functional group displacement observed in the calculations.
Falcetta, Michael F; Fair, Mark C; Tharnish, Emily M; Williams, Lorna M; Hayes, Nathan J; Jordan, Kenneth D
2016-03-14
The stabilization method is used to calculate the complex potential energy curve of the (2)Π state of CO(-) as a function of bond length, with the refinement that separate potentials are determined for p-wave and d-wave attachment and detachment of the excess electron. Using the resulting complex potentials, absolute vibrational excitation cross sections are calculated as a function of electron energy and scattering angle. The calculated cross sections agree well with experiment. PMID:26979689
NASA Astrophysics Data System (ADS)
Falcetta, Michael F.; Fair, Mark C.; Tharnish, Emily M.; Williams, Lorna M.; Hayes, Nathan J.; Jordan, Kenneth D.
2016-03-01
The stabilization method is used to calculate the complex potential energy curve of the 2Π state of CO- as a function of bond length, with the refinement that separate potentials are determined for p-wave and d-wave attachment and detachment of the excess electron. Using the resulting complex potentials, absolute vibrational excitation cross sections are calculated as a function of electron energy and scattering angle. The calculated cross sections agree well with experiment.
NASA Technical Reports Server (NTRS)
Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Arnold, James O. (Technical Monitor)
1996-01-01
The vibrational frequencies and infrared intensities of naphthalene neutral and cation are studied at the self-consistent-field (SCF), second-order Moller-Plesset (MP2), and density functional theory (DFT) levels using a variety of one-particle basis sets. Very accurate frequencies can be obtained at the DFT level in conjunction with large basis sets if they are scaled with two factors, one for the C-H stretches and a second for all other modes. We also find remarkably good agreement at the B3LYP/4-31G level using only one scale factor. Unlike the neutral PAHs where all methods do reasonably well for the intensities, only the DFT results are accurate for the PAH cations. The failure of the SCF and MP2 methods is caused by symmetry breaking and an inability to describe charge delocalization. We present several interesting cases of symmetry breaking in this study. An assessment is made as to whether an ensemble of PAH neutrals or cations could account for the unidentified infrared bands observed in many astronomical sources.
Park, G. Barratt
2014-10-07
Franck-Condon vibrational overlap integrals for the A{sup ~1}A{sub u}—X{sup ~1}Σ{sup +}{sub g} transition in acetylene have been calculated in full dimension in the harmonic normal mode basis. The calculation uses the method of generating functions first developed for polyatomic Franck-Condon factors by Sharp and Rosenstock [J. Chem. Phys. 41(11), 3453–3463 (1964)], and previously applied to acetylene by Watson [J. Mol. Spectrosc. 207(2), 276–284 (2001)] in a reduced-dimension calculation. Because the transition involves a large change in the equilibrium geometry of the electronic states, two different types of corrections to the coordinate transformation are considered to first order: corrections for axis-switching between the Cartesian molecular frames and corrections for the curvilinear nature of the normal modes at large amplitude. The angular factor in the wave function for the out-of-plane component of the trans bending mode, ν{sub 4}{sup ″}, is treated as a rotation, which results in an Eckart constraint on the polar coordinates of the bending modes. To simplify the calculation, the other degenerate bending mode, ν{sub 5}{sup ″}, is integrated in the Cartesian basis and later transformed to the constrained polar coordinate basis, restoring the conventional v and l quantum numbers. An updated A{sup ~}-state harmonic force field obtained recently in the R. W. Field research group is evaluated. The results for transitions involving the gerade vibrational modes are in qualitative agreement with experiment. Calculated results for transitions involving ungerade modes are presented in Paper II of this series [G. B. Park, J. H. Baraban, and R. W. Field, “Full dimensional Franck–Condon factors for the acetylene A{sup ~1}A{sub u}—X{sup ~1}Σ{sup +}{sub g} transition. II. Vibrational overlap factors for levels involving excitation in ungerade modes,” J. Chem. Phys. 141, 134305 (2014)].
Wirz, Lukas N; Tonner, Ralf; Hermann, Andreas; Sure, Rebecca; Schwerdtfeger, Peter
2016-01-01
We introduce a simple but computationally very efficient harmonic force field, which works for all fullerene structures and includes bond stretching, bending, and torsional motions as implemented into our open-source code Fullerene. This gives accurate geometries and reasonably accurate vibrational frequencies with root mean square deviations of up to 0.05 for bond distances and 45.5 cm(-1) for vibrational frequencies compared with more elaborate density functional calculations. The structures obtained were used for density functional calculations of Goldberg-Coxeter fullerenes up to C980 . This gives a rather large range of fullerenes making it possible to extrapolate to the graphene limit. Periodic boundary condition calculations using density functional theory (DFT) within the projector augmented wave method gave an energy difference between -8.6 and -8.8 kcal/mol at various levels of DFT for the reaction C60 ?graphene (per carbon atom) in excellent agreement with the linear extrapolation to the graphene limit (-8.6 kcal/mol at the Perdew-Burke-Ernzerhof level of theory). 2015 Wiley Periodicals, Inc. PMID:25821044
A Refined Quartic Forcefield for Acetylene: Accurate Calculation of the Vibrational Spectrum
NASA Astrophysics Data System (ADS)
Bramley, M. J.; Carter, S.; Handy, N. C.; Mills, I. M.
1993-02-01
It is now possible to calculate the nine-dimensional rovibrational wavefunctions of sequentially bonded four-atom molecules variationally without dynamical approximation. In the case of HCCH, the simplest such molecule, many hundreds of rovibrational (J = 0, 1, 2) levels can be converged to better than 1.5 cm -1. Variational calculations of this kind are used here systematically to refine the well-known quartic valence-coordinate forcefleld of Strey and Mills [J.Mol. Spectrosc.59, 103-115 (1976)] against experimental term values up to three C-H stretch quanta for the principal and two deuterated isotopomers, yielding a new surface that reproduces the energies of all the known ?, ?, and ? states of these species up to the energy of two C-H stretch quanta with an rms error of 3 cm-1 . The refined forcefield is used to study the resonances associated with the accidental degeneracies (?2 + ?4 + ?5, ?3) and (?2 + 2?5, ?1) in the principal isotopomer, leading to a clarification of the assignment of she experimentally detected states in the 2?3 and 3?3, polyads, and to the finding that vibrational Coriolis (kinetic energy) terms, rather than quartic anharmonicities in the potential, are the primary cause of the resonant interactions. Using a new cubic ab initio electric dipole field to calculate IR absorption coefficients, 24 undetected ? and ? states of 1H12C12C1H and 5 undetected ? states of D12C12CD are identified as candidates for experimental study, and their calculated energies and assignments are given.
NASA Astrophysics Data System (ADS)
Takahashi, Masae; Ishikawa, Yoichi; Ito, Hiromasa
2013-03-01
A weak hydrogen bond (WHB) such as CH-O is very important for the structure, function, and dynamics in a chemical and biological system WHB stretching vibration is in a terahertz (THz) frequency region Very recently, the reasonable performance of dispersion-corrected first-principles to WHB has been proven. In this lecture, we report dispersion-corrected first-principles calculation of the vibrational absorption of some organic crystals, and low-temperature THz spectral measurement, in order to clarify WHB stretching vibration. The THz frequency calculation of a WHB crystal has extremely improved by dispersion correction. Moreover, the discrepancy in frequency between an experiment and calculation and is 10 1/cm or less. Dispersion correction is especially effective for intermolecular mode. The very sharp peak appearing at 4 K is assigned to the intermolecular translational mode that corresponds to WHB stretching vibration. It is difficult to detect and control the WHB formation in a crystal because the binding energy is very small. With the help of the latest intense development of experimental and theoretical technique and its careful use, we reveal solid-state WHB stretching vibration as evidence for the WHB formation that differs in respective WHB networks The research was supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grant No. 22550003).
Anitha, R; Gunasekaran, M; Kumar, S Suresh; Athimoolam, S; Sridhar, B
2015-11-01
The common house hold pharmaceutical drug, paracetamol (PAR), has been synthesized from 4-chloroaniline as a first ever report. After the synthesis, good quality single crystals were obtained for slow evaporation technique under the room temperature. The crystal and molecular structures were re-determined by the single crystal X-ray diffraction. The vibrational spectral measurements were carried out using FT-IR and FT-Raman spectroscopy in the range of 4000-400 cm(-1). The single crystal X-ray studies shows that the drug crystallized in the monoclinic system polymorph (Form-I). The crystal packing is dominated by N-H?O and O-H?O classical hydrogen bonds. The ac diagonal of the unit cell features two chain C(7) and C(9) motifs running in the opposite directions. These two chain motifs are cross-linked to each other to form a ring R4(4)(22) motif and a chain C2(2)(6) motif which is running along the a-axis of the unit cell. Along with the classical hydrogen bonds, the methyl group forms a weak C-H?O interactions in the crystal packing. It offers the support for molecular assembly especially in the hydrophilic regions. Further, the strength of the hydrogen bonds are studied the shifting of vibrational bands. Geometrical optimizations of the drug molecule were done by the Density Functional Theory (DFT) using the B3LYP function and Hartree-Fock (HF) level with 6-311++G(d,p) basis set. The optimized molecular geometry and computed vibrational spectra are compared with experimental results which show significant agreement. The factor group analysis of the molecule was carried out by the various molecular symmetry, site and factor group species using the standard correlation method. The Natural Bond Orbital (NBO) analysis was carried out to interpret hyperconjugative interaction and intramolecular charge transfer (ICT). The chemical softness, chemical hardness, electro-negativity, chemical potential and electrophilicity index of the molecule were found out first time by HOMO-LUMO plot. The frontier orbitals shows lower band gap values signify the possible biological/pharmaceutical activity of the molecule. The thermodynamical properties are also obtained from the calculated frequencies of the optimized structures. PMID:26072380
NASA Astrophysics Data System (ADS)
Arjunan, V.; Balamourougane, P. S.; Saravanan, I.; Mohan, S.
2009-10-01
The Fourier transform infrared (FTIR) and FT-Raman spectra of 2-nitro-m-xylene (2NMX), 4-nitro-m-xylene (4NMX) and 5-nitro-m-xylene (5NMX) have been recorded in the range 4000-400 and 4000-100 cm -1, respectively. The experimental vibrational frequency was compared with that obtained theoretically by ab initio HF and DFT-B3LYP gradient calculations employing the standard 6-31G(d,p) basis set for the optimised geometries of the compounds. The complete vibrational assignment, analysis and correlation of the fundamental modes of the compounds were carried out using the experimental FTIR and FT-Raman data, and ab initio and DFT quantum chemical studies. The geometrical parameters and the wavenumbers of normal modes of vibration obtained from the HF and DFT methods are in good agreement with the experimental values. The potential energy distribution of the fundamental modes was calculated with ab initio force fields utilising Wilson's FG matrix method. The influence of bulky methyl groups on the nitro group fundamental modes and on the ring skeletal vibrations are investigated.
NASA Astrophysics Data System (ADS)
Leadenham, S.; Erturk, A.
2014-11-01
Over the past few years, nonlinear oscillators have been given growing attention due to their ability to enhance the performance of energy harvesting devices by increasing the frequency bandwidth. Duffing oscillators are a type of nonlinear oscillator characterized by a symmetric hardening or softening cubic restoring force. In order to realize the cubic nonlinearity in a cantilever at reasonable excitation levels, often an external magnetic field or mechanical load is imposed, since the inherent geometric nonlinearity would otherwise require impractically high excitation levels to be pronounced. As an alternative to magnetoelastic structures and other complex forms of symmetric Duffing oscillators, an M-shaped nonlinear bent beam with clamped end conditions is presented and investigated for bandwidth enhancement under base excitation. The proposed M-shaped oscillator made of spring steel is very easy to fabricate as it does not require extra discrete components to assemble, and furthermore, its asymmetric nonlinear behavior can be pronounced yielding broadband behavior under low excitation levels. For a prototype configuration, linear and nonlinear system parameters extracted from experiments are used to develop a lumped-parameter mathematical model. Quadratic damping is included in the model to account for nonlinear dissipative effects. A multi-term harmonic balance solution is obtained to study the effects of higher harmonics and a constant term. A single-term closed-form frequency response equation is also extracted and compared with the multi-term harmonic balance solution. It is observed that the single-term solution overestimates the frequency of upper saddle-node bifurcation point and underestimates the response magnitude in the large response branch. Multi-term solutions can be as accurate as time-domain solutions, with the advantage of significantly reduced computation time. Overall, substantial bandwidth enhancement with increasing base excitation is validated experimentally, analytically, and numerically. As compared to the 3 dB bandwidth of the corresponding linear system with the same linear damping ratio, the M-shaped oscillator offers 3200, 5600, and 8900 percent bandwidth enhancement at the root-mean-square base excitation levels of 0.03g, 0.05g, and 0.07g, respectively. The M-shaped configuration can easily be exploited in piezoelectric and electromagnetic energy harvesting as well as their hybrid combinations due to the existence of both large strain and kinetic energy regions. A demonstrative case study is given for electromagnetic energy harvesting, revealing the importance of higher harmonics and the need for multi-term harmonic balance analysis for predicting the electrical power output accurately.
Carter, S.; Bowman, J.M.
2000-03-23
The authors report variational calculations of vibrational energies of CH{sub 4}, CH{sub 3}D, CH{sub 2}D{sub 2}, CHD{sub 3}, and CD{sub 4} using the code Multimode and the ab initio force field of Lee and co-workers [Lee, T.J.; Martin, J.M.L.; Taylor, P.R.--J.Chem.Phys. 1995, 102, 254], re-expressed using Morse variables in the stretch displacements. Comparisons are made with experimental energies for CH{sub 4} with this potential, and then small adjustments are made to the potential to improve agreement with experiment for CH{sub 4}. Calculations for the isotopomers are done using the adjusted potential and compared with experiment. Additional vibrational energies and assignments not reported experimentally are also given for CH{sub 4} and the isotopomers. Exact rotational-vibrational energies of CH{sub 4} are also reported for J = 1.
Ramalingam, S; Periandy, S; Elanchezhian, B; Mohan, S
2011-01-01
FT-IR (4000-100 cm(-1)) and FT-Raman (4000-100 cm(-1)) spectra of solid sample of 4-chloro-2-fluoro toluene (4Cl2FT) have been recorded using Bruker IFS 66 V spectrometer. Ab initio-HF (HF/6-311++G (d, p)) and DFT (B3LYP/6-311++G and B3PW91/6-311++G (d, p)) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, IR intensities, Raman activities. The vibrational frequencies are calculated and scaled values are compared with FT-IR and FT-Raman experimental values. The isotropic HF and DFT analyses showed good agreement with experimental observations. The differences between the observed and scaled wave number values of most of the fundamentals are very small in B3LYP than HF. Comparison of the simulated spectra provides important information about the ability of the computational method (B3LYP) to describe the vibrational modes. The influences of substitutions on the geometry of molecule and its normal modes of vibrations have also been discussed. The changes made by substitutions on the benzene are much responsible for the non-linearity of the molecule. This is an attractive entity for the future studies of non-linear optics. PMID:21146451
Tonannavar, J; Yenagi, Jayashree; Sortur, Veenasangeeta; Jadhav, V B; Kulkarni, M V
2010-10-01
Vibration spectral measurements - Infrared (4000-400 cm(-1)) and Raman (3500-50 cm(-1)) spectra - have been made for the solid samples of 6-Chloro- and 7-Chloro-4-bromomethylcoumarins. Ground electronic state energies, equilibrium geometries, harmonic vibrational spectra and normal modes have been computed using ab initio - RHF/6-31G* - and DFT - B3LYP/6-31G* levels of theory. The optimization yielded three structures for each molecule, with one being a transition state structure. Of the remaining two conformers, one belongs to C(s) symmetry and the other belongs to C(1), the latter being the most stable one. The optimized dihedral angle for -CH(2)Br group is 111 degrees in agreement with X-ray diffraction results reported for the similar molecular systems. Assignment of all the observed spectral bands has been proposed. The absorptions show band pattern revealing isomer characteristics and vibrational coupling in varying degrees; the Raman spectra show structural changes associated with the rings as well as lattice modes. PMID:20638328
Vibrational spectroscopic studies and ab initio calculations of Goniothalamin, a natural product
NASA Astrophysics Data System (ADS)
Harikumar, B.; Varghese, Hema Tresa; Panicker, C. Yohannan; Jayakumar, G.
2008-11-01
5,6-Dihydro-6-styryl-2-pyrone ( Goniothalamin), is isolated from the leaves of Goniothalamus wightii and identified by spectral analysis and X-ray diffraction studies. FT-IR spectroscopy has also been used to characterize the vibrational bands. The vibrational wavenumbers and corresponding vibrational assignments are examined theoretically using the Gaussian03 set of quantum chemistry codes. Predicted IR and Raman intensities are reported.
Gobinath, E; Xavier, R John
2013-03-01
The complete vibrational assignment and analysis of the fundamental modes of 2-bromo-5-nitrothiazole (BNT) was carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the ab initio HF and DFT-B3LYP gradient calculations employing 6-311++G(d,p) basis set. Thermodynamic properties like entropy, heat capacity and zero point energy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of BNT have been computed using B3LYP quantum chemical calculation. PMID:23274373
NASA Astrophysics Data System (ADS)
Nolasco, Mariela M.; Vaz, Patrícia M.; Vaz, Pedro D.; Ribeiro-Claro, Paulo J. A.
2012-11-01
The complete vibrational spectra assignment of dihydrocoumarin is performed through a combined vibrational spectroscopy and DFT calculations approach. To provide effective information, vibrational analysis was also performed for α-pyrone and coumarin related systems. The presence of extra components in the νCdbnd O band profile can only be understood by both Fermi resonance and monomer/dimer equilibrium phenomena, the latter established by C-H···O hydrogen bond with ΔH° value of -8.4 ± 0.9 kJ mol-1. The analysis of the νC-H region indicates that both the methylene and aromatic C-H groups have a significant contribution to the formation of C-H···O bonded dimers in liquid dihydrocoumarin.
NASA Astrophysics Data System (ADS)
Xie, Daiqian; Ma, Guobin; Guo, Hua
1999-11-01
We report quantum mechanical calculations of the X?C emission spectra of SO2 at the red wing of the C absorption band. The near equilibrium potential energy surface of the C 1B2 state is deduced by fitting experimental vibrational frequencies using an exact quantum mechanical Hamiltonian. Low-lying vibrational eigenenergies on this double minimum potential agree well with experimental frequencies and the corresponding eigenstates show some interesting features. Both spectral positions and intensities of the X?C transitions are obtained up to 16 000 cm-1 using a Chebyshev based spectral method, which does not explicitly construct vibrational eigenfunctions in the X state. The emission spectra are in reasonably good agreement with experimental measurements.
NASA Astrophysics Data System (ADS)
Yu, Hua-Gen; Ndengue, Steve; Li, Jun; Dawes, Richard; Guo, Hua
2015-08-01
Accurate vibrational energy levels of the simplest Criegee intermediate (CH2OO) were determined on a recently developed ab initio based nine-dimensional potential energy surface using three quantum mechanical methods. The first is the iterative Lanczos method using a conventional basis expansion with an exact Hamiltonian. The second and more efficient method is the multi-configurational time-dependent Hartree (MCTDH) method in which the potential energy surface is refit to conform to the sums-of-products requirement of MCTDH. Finally, the energy levels were computed with a vibrational self-consistent field/virtual configuration interaction method in MULTIMODE. The low-lying levels obtained from the three methods are found to be within a few wave numbers of each other, although some larger discrepancies exist at higher levels. The calculated vibrational levels are very well represented by an anharmonic effective Hamiltonian.
Zhan, Meng; Liu, Shuai; He, Zhiwei
2013-01-01
The structure-dynamics-function has become one of central problems in modern sciences, and it is a great challenge to unveil the organization rules for different dynamical processes on networks. In this work, we study the vibration spectra of the classical mass spring model with different masses on complex networks, and pay our attention to how the mass spatial configuration influences the second-smallest vibrational frequency () and the largest one (). For random networks, we find that becomes maximal and becomes minimal if the node degrees are point-to-point-positively correlated with the masses. In these cases, we call it point-to-point matching. Moreover, becomes minimal under the condition that the heaviest mass is placed on the lowest-degree vertex, and is maximal as long as the lightest mass is placed on the highest-degree vertex, and in both cases all other masses can be arbitrarily settled. Correspondingly, we call it single-point matching. These findings indicate that the matchings between the node dynamics (parameter) and the node position rule the global systems dynamics, and sometimes only one node is enough to control the collective behaviors of the whole system. Therefore, the matching rules might be the common organization rules for collective behaviors on networks. PMID:24386088
Zhan, Meng; Liu, Shuai; He, Zhiwei
2013-01-01
The structure-dynamics-function has become one of central problems in modern sciences, and it is a great challenge to unveil the organization rules for different dynamical processes on networks. In this work, we study the vibration spectra of the classical mass spring model with different masses on complex networks, and pay our attention to how the mass spatial configuration influences the second-smallest vibrational frequency (?2) and the largest one (?N). For random networks, we find that ?2 becomes maximal and ?N becomes minimal if the node degrees are point-to-point-positively correlated with the masses. In these cases, we call it point-to-point matching. Moreover, ?2 becomes minimal under the condition that the heaviest mass is placed on the lowest-degree vertex, and ?N is maximal as long as the lightest mass is placed on the highest-degree vertex, and in both cases all other masses can be arbitrarily settled. Correspondingly, we call it single-point matching. These findings indicate that the matchings between the node dynamics (parameter) and the node position rule the global systems dynamics, and sometimes only one node is enough to control the collective behaviors of the whole system. Therefore, the matching rules might be the common organization rules for collective behaviors on networks. PMID:24386088
Kodama, Tomoaki; Honda, Yasuhiro; Wakabayashi, Katsuhiko; Iwamoto, Shoichi
1996-09-01
The cheap and compact rubber dampers of shear-type have been widely employed as the torsional vibration control of the crankshaft system of high-speed, automobile diesel engines. The conventional rubber dampers have various rubber forms owing to the thorough investigation of optimum dampers in the design stage. Their rubber forms can be generally grouped into three classes such as the disk type, the bush type and the composite type. The disk type and the bush type rubber dampers are called the basic-pattern rubber dampers hereafter. The composite type rubber part is supposed to consist of the disk type and the bush type parts, regarded respectively as the basic patterns of the rubber part, at large. The dynamic characteristics of the vibration isolator rubber depend generally on temperature, frequency, strain amplitude, shape and size effect,s so it is difficult to estimate accurately their characteristics. With the present technical level, it is also difficult to determine the suitable rubber geometry which optimizes the vibration control effect. The study refers to the calculation method of the torsional vibration of a crankshaft system with a shear-type rubber damper having various rubber forms in order to offer the useful method for optimum design. In this method, the rheological formula of the three-element Maxwell model, from which the torsional stiffness and the damping coefficient of the damper rubber part in the equivalent vibration system are obtained, are adopted in order to decide the dynamic characteristics of the damper rubber part.
NASA Astrophysics Data System (ADS)
Coudeyras, N.; Sinou, J.-J.; Nacivet, S.
2009-01-01
Brake squeal noise is still an issue since it generates high warranty costs for the automotive industry and irritation for customers. Key parameters must be known in order to reduce it. Stability analysis is a common method of studying nonlinear phenomena and has been widely used by the scientific and the engineering communities for solving disc brake squeal problems. This type of analysis provides areas of stability versus instability for driven parameters, thereby making it possible to define design criteria. Nevertheless, this technique does not permit obtaining the vibrating state of the brake system and nonlinear methods have to be employed. Temporal integration is a well-known method for computing the dynamic solution but as it is time consuming, nonlinear methods such as the Harmonic Balance Method (HBM) are preferred. This paper presents a novel nonlinear method called the Constrained Harmonic Balance Method (CHBM) that works for nonlinear systems subject to flutter instability. An additional constraint-based condition is proposed that omits the static equilibrium point (i.e. the trivial static solution of the nonlinear problem that would be obtained by applying the classical HBM) and therefore focuses on predicting both the Fourier coefficients and the fundamental frequency of the stationary nonlinear system. The effectiveness of the proposed nonlinear approach is illustrated by an analysis of disc brake squeal. The brake system under consideration is a reduced finite element model of a pad and a disc. Both stability and nonlinear analyses are performed and the results are compared with a classical variable order solver integration algorithm. Therefore, the objectives of the following paper are to present not only an extension of the HBM (CHBM) but also to demonstrate an application to the specific problem of disc brake squeal with extensively parametric studies that investigate the effects of the friction coefficient, piston pressure, nonlinear stiffness and structural damping.
Pasha, M A; Siddekha, Aisha; Mishra, Soni; Azzam, Sadeq Hamood Saleh; Umapathy, S
2015-02-01
In the present study, 2'-nitrophenyloctahydroquinolinedione and its 3'-nitrophenyl isomer were synthesized and characterized by FT-IR, FT-Raman, (1)H NMR and (13)C NMR spectroscopy. The molecular geometry, vibrational frequencies, (1)H and (13)C NMR chemical shift values of the synthesized compounds in the ground state have been calculated by using the density functional theory (DFT) method with the 6-311++G (d,p) basis set and compared with the experimental data. The complete vibrational assignments of wave numbers were made on the basis of potential energy distribution using GAR2PED programme. Isotropic chemical shifts for (1)H and (13)C NMR were calculated using gauge-invariant atomic orbital (GIAO) method. The experimental vibrational frequencies, (1)H and (13)C NMR chemical shift values were found to be in good agreement with the theoretical values. On the basis of vibrational analysis, molecular electrostatic potential and the standard thermodynamic functions have been investigated. PMID:25440584
NASA Astrophysics Data System (ADS)
Majumder, Moumita; Dawes, Richard; Wang, Xiao-Gang; Carrington, Tucker; Li, Jun; Guo, Hua; Manzhos, Sergei
2014-06-01
New potential energy surfaces for methane were constructed, represented as analytic fits to about 100,000 individual high-level ab initio data. Explicitly-correlated multireference data (MRCI-F12(AE)/CVQZ-F12) were computed using Molpro [1] and fit using multiple strategies. Fits with small to negligible errors were obtained using adaptations of the permutation-invariant-polynomials (PIP) approach [2,3] based on neural-networks (PIP-NN) [4,5] and the interpolative moving least squares (IMLS) fitting method [6] (PIP-IMLS). The PESs were used in full-dimensional vibrational calculations with an exact kinetic energy operator by representing the Hamiltonian in a basis of products of contracted bend and stretch functions and using a symmetry adapted Lanczos method to obtain eigenvalues and eigenvectors. Very close agreement with experiment was produced from the purely ab initio PESs. References 1- H.-J. Werner, P. J. Knowles, G. Knizia, 2012.1 ed. 2012, MOLPRO, a package of ab initio programs. see http://www.molpro.net. 2- Z. Xie and J. M. Bowman, J. Chem. Theory Comput 6, 26, 2010. 3- B. J. Braams and J. M. Bowman, Int. Rev. Phys. Chem. 28, 577, 2009. 4- J. Li, B. Jiang and Hua Guo, J. Chem. Phys. 139, 204103 (2013). 5- S Manzhos, X Wang, R Dawes and T Carrington, JPC A 110, 5295 (2006). 6- R. Dawes, X-G Wang, A.W. Jasper and T. Carrington Jr., J. Chem. Phys. 133, 134304 (2010).
Vibrational spectrum of p-fluoroanisole in the first excited state (S 1) and ab initio calculations
NASA Astrophysics Data System (ADS)
Xiao, Daoqing; Yu, Dan; Xu, Xiling; Yu, Zijun; Du, Yikui; Gao, Zhen; Zhu, Qihe; Zhang, Cunhao
2008-06-01
The vibronic structure of p-fluoroanisole in the first excited state (S 1) has been investigated with mass selected resonance-enhanced two photon ionization spectroscopy. The band origin of S 1 ← S 0 transition of p-fluoroanisole is measured to be 35149 cm -1, which is red-shifted by 1234 cm -1 with respect to that of anisole. Combining with the ab initio calculations, the measured frequencies 397, 487, 559, 840 and 1150 cm -1 in the S 1 state are assigned as the in-plane ring vibrational mode 9 b, 6 a, 6 b, 1 and 9 a, respectively. The optimized molecular geometries and vibrational frequencies of p-fluoroanisole in the ground state (S 0) and cation ground state (D 0) are also achieved from DFT calculations.
NASA Astrophysics Data System (ADS)
Page, Alexander; Uher, Ctirad; Poudeu, Pierre Ferdinand; Van der Ven, Anton
2015-11-01
Previous studies have indicated that the figure of merit (ZT ) of half-Heusler (HH) alloys with composition M NiSn (M =Ti , Zr, or Hf) is greatly enhanced when the alloys contain a nano-scale full-Heusler (FH) MN i2Sn second phase. However, the formation mechanism of the FHnanostructures in the HH matrix and their vibrational properties are still not well understood. We report on first-principles studies of thermodynamic phase equilibria in the MNiSn-MN i2Sn pseudobinary system as well as HH and FH vibrational properties. Thermodynamic phase diagrams as functions of temperature and Ni concentration were developed using density functional theory (DFT) combined with a cluster expansion and Monte Carlo simulations. The phase diagrams show very low excess Ni solubility in HH alloys even at high temperatures, which indicates that any Ni excess will decompose into a two-phase mixture of HH and FH compounds. Vibrational properties of HH and FH alloys are compared. Imaginary vibrational modes in the calculated phonon dispersion diagram of TiN i2Sn indicate a dynamical instability with respect to cubic [001] transverse acoustic modulations. Displacing atoms along unstable vibrational modes in cubic TiN i2Sn reveals lower-energy structures with monoclinic symmetry. The energy of the monoclinic structures is found to depend strongly on the lattice parameter. The origin of the instability in cubic TiN i2Sn and its absence in cubic ZrN i2Sn and HfN i2Sn is attributed to the small size of the Ti 3 d shells compared to those of Zr and Hf atoms. Lattice constants and heat capacities calculated by DFT agree well with experiment.
NASA Astrophysics Data System (ADS)
Bonello, Philip; Minh Hai, Pham
2009-07-01
Current frequency-domain techniques for the rapid computation of the steady-state periodic vibration of unbalanced rotordynamic systems with nonlinear bearings are not suitable for realistic engine structures like aero-engine assemblies. In this paper, a whole-engine receptance harmonic balance method (RHBM) is devised that, for the first time, allows the frequency domain analysis of such a structure. The method uses the receptance functions of the linear part of the structure under non-rotational conditions, obtained from a one-off eigenvalue analysis, to set up the equations for the rotating nonlinear assembly. The unknowns solved for are the Fourier coefficients of the relative displacements at the nonlinear bearings plus a few extra unknowns. These latter unknowns enable solution of the problem in the presence of statically indeterminate rotors that have just one linear point support or none at all. Simulation tests on a realistically sized representative twin-spool engine showed excellent correlation with time-marching results obtained from the recently developed impulsive receptance method (IRM). It is demonstrated that, when used in conjunction with a time-marching solver like the IRM, the RHBM is a very powerful tool that should greatly facilitate the hitherto highly restricted nonlinear dynamic analysis of realistic engine structures.
Brizuela, Alicia Beatriz; Castillo, Mara Victoria; Raschi, Ana Beatriz; Davies, Lilian; Romano, Elida; Brandn, Silvia Antonia
2014-03-31
In the present study, a complete assignment of the vibrational spectra of sucrose in aqueous medium was performed combining Pulay's Scaled Quantum Mechanics Force Field (SQMFF) methodology with self-consistent reaction field (SCRF) calculations. Aqueous saturated solutions of sucrose and solutions at different molar concentrations of sucrose in water were completely characterized by infrared, HATR, and Raman spectroscopies. In accordance with reported data of the literature for sucrose, the theoretical structures of sucrose penta and sucrose dihydrate were also optimized in gas and aqueous solution phases by using the density functional theory (DFT) calculations. The solvent effects for the three studied species were analyzed using the solvation PCM/SMD model and, then, their corresponding solvation energies were predicted. The presence of pure water, sucrose penta-hydrate, and sucrose dihydrate was confirmed by using theoretical calculations based on the hybrid B3LYP/6-31G(?) method and the experimental vibrational spectra. The existence of both sucrose hydrate complexes in aqueous solution is evidenced in the IR and HATR spectra by means of the characteristic bands at 3388, 3337, 3132, 1648, 1375, 1241, 1163, 1141, 1001, 870, 851, 732, and 668cm(-1) while in the Raman spectrum, the groups of bands in the regions 3159-3053cm(-1), 2980, 2954, and 1749-1496cm(-1) characterize the vibration modes of those complexes. The inter and intra-molecular H bond formations in aqueous solution were studied by Natural Bond Orbital (NBO) and Atoms in Molecules theory (AIM) investigation. PMID:24632216
Accurate quantum dynamics calculations of vibrational spectrum of dideuteromethane CH{sub 2}D{sub 2}
Yu, Hua-Gen
2015-05-21
We report a rigorous variational study of the infrared (IR) vibrational spectra of both CH{sub 2}D{sub 2} and {sup 13}CH{sub 2}D{sub 2} isotopomers using an exact molecular Hamiltonian. Calculations are carried out using a recently developed multi-layer Lanczos algorithm based on the accurate refined Wang and Carrington potential energy surface of methane and the low-order truncated ab initio dipole moment surface of Yurchenko et al. [J. Mol. Spectrosc. 291, 69 (2013)]. All well converged 357 vibrational energy levels up to 6100 cm{sup ?1} of CH{sub 2}D{sub 2} are obtained, together with a comparison to previous calculations and 91 experimental bands available. The calculated frequencies are in excellent agreement with the experimental results and give a root-mean-square error of 0.67?cm{sup ?1}. In particular, we also compute the transition intensities from the vibrational ground state for both isotopomers. Based on the theoretical results, 20 experimental bands are suggested to be re-assigned. Surprisingly, an anomalous C isotopic effect is discovered in the n?{sub 5} modes of CH{sub 2}D{sub 2}. The predicted IR spectra provide useful information for understanding those unknown bands.
NASA Astrophysics Data System (ADS)
Kannan, V.; Thirupugalmani, K.; Brahadeeswaran, S.
2013-10-01
Single crystals of N-Succinopyridine (NSP) have been grown from water using solution growth method by isothermal solvent evaporation technique. The solid state Fourier Transform Infrared (FTIR) spectrum of the grown crystal shows a broad absorption extending from 3450 down to 400 cm-1, due to H-bond vibrations and other characteristic vibrations. Fourier Transform Raman (FT-Raman) spectrum of NSP single crystal shows Raman intensities ranging from 3100 to 100 cm-1 due the characteristics vibrations of functional groups present in NSP. The proton and carbon positions of NSP have been described by 1H and 13C NMR spectrum respectively. Ab initio quantum chemical calculations on NSP have been performed by density functional theory (DFT) calculations using B3LYP method with 6-311++G(d,p) basis set. The predicted first hyperpolarizability is found to be 1.29 times greater than that of urea and suggests that the title compound could be an attractive material for nonlinear optical applications. The calculated HOMO-LUMO energies show that charge transfers occur within the molecule and other related molecular properties. Molecular properties such as Mulliken population analysis, thermodynamic functions and perturbation theory energy analysis have also been reported. Electrostatic potential map (ESP) of NSP obtained by electron density isosurface provided the information about the size, shape, charge density distribution and site of chemical reactivity of the title molecule. The molecular stability and bond strength have been investigated through the Natural Bond Orbital (NBO) analysis.
NASA Astrophysics Data System (ADS)
Appalakondaiah, S.; Vaitheeswaran, G.; Lebgue, S.
2014-01-01
The effects of pressure on the structural and vibrational properties of the layered molecular crystal 1,1-diamino-2,2-dinitroethelene (FOX-7) are explored by first principles calculations. We observe significant changes in the calculated structural properties with different corrections for treating van der Waals interactions to Density Functional Theory (DFT), as compared with standard DFT functionals. In particular, the calculated ground state lattice parameters, volume and bulk modulus obtained with Grimme's scheme, are found to agree well with experiments. The calculated vibrational frequencies demonstrate the dependence of the intra and inter-molecular interactions on FOX-7 under pressure. In addition, we also found a significant increment in the N-H...O hydrogen bond strength under compression. This is explained by the change in bond lengths between nitrogen, hydrogen, and oxygen atoms, as well as calculated IR spectra under pressure. Finally, the computed band gap is about 2.3 eV with generalized gradient approximation, and is enhanced to 5.1 eV with the GW approximation, which reveals the importance of performing quasiparticle calculations in high energy density materials.
Appalakondaiah, S; Vaitheeswaran, G; Lebègue, S
2014-01-01
The effects of pressure on the structural and vibrational properties of the layered molecular crystal 1,1-diamino-2,2-dinitroethelene (FOX-7) are explored by first principles calculations. We observe significant changes in the calculated structural properties with different corrections for treating van der Waals interactions to Density Functional Theory (DFT), as compared with standard DFT functionals. In particular, the calculated ground state lattice parameters, volume and bulk modulus obtained with Grimme's scheme, are found to agree well with experiments. The calculated vibrational frequencies demonstrate the dependence of the intra and inter-molecular interactions on FOX-7 under pressure. In addition, we also found a significant increment in the N-H...O hydrogen bond strength under compression. This is explained by the change in bond lengths between nitrogen, hydrogen, and oxygen atoms, as well as calculated IR spectra under pressure. Finally, the computed band gap is about 2.3 eV with generalized gradient approximation, and is enhanced to 5.1 eV with the GW approximation, which reveals the importance of performing quasiparticle calculations in high energy density materials. PMID:24410219
Appalakondaiah, S.; Vaitheeswaran, G.; Lebègue, S.
2014-01-07
The effects of pressure on the structural and vibrational properties of the layered molecular crystal 1,1-diamino-2,2-dinitroethelene (FOX-7) are explored by first principles calculations. We observe significant changes in the calculated structural properties with different corrections for treating van der Waals interactions to Density Functional Theory (DFT), as compared with standard DFT functionals. In particular, the calculated ground state lattice parameters, volume and bulk modulus obtained with Grimme's scheme, are found to agree well with experiments. The calculated vibrational frequencies demonstrate the dependence of the intra and inter-molecular interactions on FOX-7 under pressure. In addition, we also found a significant increment in the N–H...O hydrogen bond strength under compression. This is explained by the change in bond lengths between nitrogen, hydrogen, and oxygen atoms, as well as calculated IR spectra under pressure. Finally, the computed band gap is about 2.3 eV with generalized gradient approximation, and is enhanced to 5.1 eV with the GW approximation, which reveals the importance of performing quasiparticle calculations in high energy density materials.
Erba, Alessandro; Maul, Jefferson; Civalleri, Bartolomeo
2016-01-21
An ab initio quantum-mechanical theoretical framework is presented to compute the thermal properties of molecular crystals. The present strategy combines dispersion-corrected density-functional-theory (DFT-D), harmonic phonon dispersion, quasi-harmonic approximation to the lattice dynamics for thermal expansion and thermodynamic functions, and quasi-static approximation for anisotropic thermo-elasticity. The proposed scheme is shown to reliably describe thermal properties of the urea molecular crystal by a thorough comparison with experimental data. PMID:26670006
NASA Astrophysics Data System (ADS)
Legler, C. R.; Brown, N. R.; Dunbar, R. A.; Harness, M. D.; Nguyen, K.; Oyewole, O.; Collier, W. B.
2015-06-01
The Scaled Quantum Mechanical (SQM) method of scaling calculated force constants to predict theoretically calculated vibrational frequencies is expanded to include a broad array of polarized and augmented basis sets based on the split valence 6-31G and 6-311G basis sets with the B3LYP density functional. Pulay's original choice of a single polarized 6-31G(d) basis coupled with a B3LYP functional remains the most computationally economical choice for scaled frequency calculations. But it can be improved upon with additional polarization functions and added diffuse functions for complex molecular systems. The new scale factors for the B3LYP density functional and the 6-31G, 6-31G(d), 6-31G(d,p), 6-31G+(d,p), 6-31G++(d,p), 6-311G, 6-311G(d), 6-311G(d,p), 6-311G+(d,p), 6-311G++(d,p), 6-311G(2d,p), 6-311G++(2d,p), 6-311G++(df,p) basis sets are shown. The double d polarized models did not perform as well and the source of the decreased accuracy was investigated. An alternate system of generating internal coordinates that uses the out-of plane wagging coordinate whenever it is possible; makes vibrational assignments via potential energy distributions more meaningful. Automated software to produce SQM scaled vibrational calculations from different molecular orbital packages is presented.
Zhang, Feng; Tominaga, Keisuke E-mail: tominaga@kobe-u.ca.jp; Hayashi, Michitoshi E-mail: tominaga@kobe-u.ca.jp Wang, Houng-Wei; Kambara, Ohki; Sasaki, Tetsuo; Nishizawa, Jun-ichi E-mail: tominaga@kobe-u.ca.jp
2014-05-07
The phonon modes of molecular crystals in the terahertz frequency region often feature delicately coupled inter- and intra-molecular vibrations. Recent advances in density functional theory such as DFT-D{sup *} have enabled accurate frequency calculation. However, the nature of normal modes has not been quantitatively discussed against experimental criteria such as isotope shift (IS) and correlation field splitting (CFS). Here, we report an analytical mode-decoupling method that allows for the decomposition of a normal mode of interest into intermolecular translation, libration, and intramolecular vibrational motions. We show an application of this method using the crystalline anthracene system as an example. The relationship between the experimentally obtained IS and the IS obtained by PBE-D{sup *} simulation indicates that two distinctive regions exist. Region I is associated with a pure intermolecular translation, whereas region II features coupled intramolecular vibrations that are further coupled by a weak intermolecular translation. We find that the PBE-D{sup *} data show excellent agreement with the experimental data in terms of IS and CFS in region II; however, PBE-D{sup *} produces significant deviations in IS in region I where strong coupling between inter- and intra-molecular vibrations contributes to normal modes. The result of this analysis is expected to facilitate future improvement of DFT-D{sup *}.
NASA Astrophysics Data System (ADS)
Weber, Wolfgang; Zastrau, Bernd W.; Anders, Bernd
2013-12-01
This contribution deals with the identification of the right-eigenvectors of a linear vibration system with arbitrary n degrees of freedom as given in [1]. Applying the special distribution of stiffnesses and masses given in [1] yields a remarkable sequence of matrices for arbi- trary n. For computing the (right-)eigenvectors a generalised approach allowing the use of Laguerre polynomials is performed.
High-order-harmonic generation from H2+ molecular ions near plasmon-enhanced laser fields
NASA Astrophysics Data System (ADS)
Yavuz, I.; Tikman, Y.; Altun, Z.
2015-08-01
Simulations of plasmon-enhanced high-order-harmonic generation are performed for a H2+ molecular cation near the metallic nanostructures. We employ the numerical solution of the time-dependent Schrdinger equation in reduced coordinates. We assume that the main axis of H2+ is aligned perfectly with the polarization direction of the plasmon-enhanced field. We perform systematic calculations on plasmon-enhanced harmonic generation based on an infinite-mass approximation, i.e., pausing nuclear vibrations. Our simulations show that molecular high-order-harmonic generation from plasmon-enhanced laser fields is possible. We observe the dispersion of a plateau of harmonics when the laser field is plasmon enhanced. We find that the maximum kinetic energy of the returning electron follows 4 Up . We also find that when nuclear vibrations are enabled, the efficiency of the harmonics is greatly enhanced relative to that of static nuclei. However, the maximum kinetic energy 4 Up is largely maintained.
Jonsson, Ulf G; Andersson, Britt M; Lindahl, Olof A
2013-01-01
To gain an understanding of the electroelastic properties of tactile piezoelectric sensors used in the characterization of soft tissue, the frequency-dependent electric impedance response of thick piezoelectric disks has been calculated using finite element modeling. To fit the calculated to the measured response, a new method was developed using harmonic overtones for tuning of the calculated effective elastic, piezoelectric, and dielectric parameters. To validate the results, the impedance responses of 10 piezoelectric disks with diameter-to-thickness ratios of 20, 6, and 2 have been measured from 10 kHz to 5 MHz. A two-dimensional, general purpose finite element partial differential equation solver with adaptive meshing capability run in the frequency-stepped mode, was used. The equations and boundary conditions used by the solver are presented. Calculated and measured impedance responses are presented, and resonance frequencies have been compared in detail. The comparison shows excellent agreement, with average relative differences in frequency of 0.27%, 0.19%, and 0.54% for the samples with diameter-to-thickness ratios of 20, 6, and 2, respectively. The method of tuning the effective elastic, piezoelectric, and dielectric parameters is an important step toward a finite element model that describes the properties of tactile sensors in detail. PMID:23287929
NASA Astrophysics Data System (ADS)
Thore, A.; Dahlqvist, M.; Alling, B.; Rosn, J.
2014-09-01
In this paper, we report the by first-principles predicted properties of the recently discovered magnetic MAX phase Mn2GaC. The electronic band structure and vibrational dispersion relation, as well as the electronic and vibrational density of states, have been calculated. The band structure close to the Fermi level indicates anisotropy with respect to electrical conductivity, while the distribution of the electronic and vibrational states for both Mn and Ga depend on the chosen relative orientation of the Mn spins across the Ga sheets in the Mn-Ga-Mn trilayers. In addition, the elastic properties have been calculated, and from the five elastic constants, the Voigt bulk modulus is determined to be 157 GPa, the Voigt shear modulus 93 GPa, and the Young's modulus 233 GPa. Furthermore, Mn2GaC is found relatively elastically isotropic, with a compression anisotropy factor of 0.97, and shear anisotropy factors of 0.9 and 1, respectively. The Poisson's ratio is 0.25. Evaluated elastic properties are compared to theoretical and experimental results for M2AC phases where M = Ti, V, Cr, Zr, Nb, Ta, and A = Al, S, Ge, In, Sn.
NASA Astrophysics Data System (ADS)
Wang, Xianwei; Zhang, John Z. H.; He, Xiao
2015-11-01
Recent advance in biophysics has made it possible to directly measure site-specific electric field at internal sites of proteins using molecular probes with C = O or C≡N groups in the context of vibrational Stark effect. These measurements directly probe changes of electric field at specific protein sites due to, e.g., mutation and are very useful in protein design. Computational simulation of the Stark effect based on force fields such as AMBER and OPLS, while providing good insight, shows large errors in comparison to experimental measurement due to inherent difficulties associated with point charge based representation of force fields. In this study, quantum mechanical calculation of protein's internal electrostatic properties and vibrational Stark shifts was carried out by using electrostatically embedded generalized molecular fractionation with conjugate caps method. Quantum calculated change of mutation-induced electric field and vibrational Stark shift is reported at the internal probing site of enzyme human aldose reductase. The quantum result is in much better agreement with experimental data than those predicted by force fields, underscoring the deficiency of traditional point charge models describing intra-protein electrostatic properties.
Thore, A. Dahlqvist, M. E-mail: bjoal@ifm.liu.se Alling, B. E-mail: bjoal@ifm.liu.se Rosén, J. E-mail: bjoal@ifm.liu.se
2014-09-14
In this paper, we report the by first-principles predicted properties of the recently discovered magnetic MAX phase Mn₂GaC. The electronic band structure and vibrational dispersion relation, as well as the electronic and vibrational density of states, have been calculated. The band structure close to the Fermi level indicates anisotropy with respect to electrical conductivity, while the distribution of the electronic and vibrational states for both Mn and Ga depend on the chosen relative orientation of the Mn spins across the Ga sheets in the Mn–Ga–Mn trilayers. In addition, the elastic properties have been calculated, and from the five elastic constants, the Voigt bulk modulus is determined to be 157 GPa, the Voigt shear modulus 93 GPa, and the Young's modulus 233 GPa. Furthermore, Mn₂GaC is found relatively elastically isotropic, with a compression anisotropy factor of 0.97, and shear anisotropy factors of 0.9 and 1, respectively. The Poisson's ratio is 0.25. Evaluated elastic properties are compared to theoretical and experimental results for M₂AC phases where M = Ti, V, Cr, Zr, Nb, Ta, and A = Al, S, Ge, In, Sn.
Wang, Xianwei; Zhang, John Z H; He, Xiao
2015-11-14
Recent advance in biophysics has made it possible to directly measure site-specific electric field at internal sites of proteins using molecular probes with C = O or C≡N groups in the context of vibrational Stark effect. These measurements directly probe changes of electric field at specific protein sites due to, e.g., mutation and are very useful in protein design. Computational simulation of the Stark effect based on force fields such as AMBER and OPLS, while providing good insight, shows large errors in comparison to experimental measurement due to inherent difficulties associated with point charge based representation of force fields. In this study, quantum mechanical calculation of protein's internal electrostatic properties and vibrational Stark shifts was carried out by using electrostatically embedded generalized molecular fractionation with conjugate caps method. Quantum calculated change of mutation-induced electric field and vibrational Stark shift is reported at the internal probing site of enzyme human aldose reductase. The quantum result is in much better agreement with experimental data than those predicted by force fields, underscoring the deficiency of traditional point charge models describing intra-protein electrostatic properties. PMID:26567650
NASA Astrophysics Data System (ADS)
Avram, C. N.; Gruia, A. S.; Brik, M. G.; Barb, A. M.
2015-12-01
Calculations of the Cr3+ energy levels, spin-Hamiltonian parameters and vibrational spectra for the layered CrCl3 crystals are reported for the first time. The crystal field parameters and the energy level scheme were calculated in the framework of the Exchange Charge Model of crystal field. The spin-Hamiltonian parameters (zero-field splitting parameter D and g-factors) for Cr3+ ion in CrCl3 crystals were obtained using two independent techniques: i) semi-empirical crystal field theory and ii) density functional theory (DFT)-based model. In the first approach, the spin-Hamiltonian parameters were calculated from the perturbation theory method and the complete diagonalization (of energy matrix) method. The infrared (IR) and Raman frequencies were calculated for both experimental and fully optimized geometry of the crystal structure, using CRYSTAL09 software. The obtained results are discussed and compared with the experimental available data.
Mielke, Steven L. E-mail: truhlar@umn.edu; Truhlar, Donald G. E-mail: truhlar@umn.edu
2015-01-28
We present an improved version of our path-by-path enhanced same path extrapolation scheme for Feynman path integral (FPI) calculations that permits rapid convergence with discretization errors ranging from O(P{sup ?6}) to O(P{sup ?12}), where P is the number of path discretization points. We also present two extensions of our importance sampling and stratified sampling schemes for calculating vibrationalrotational partition functions by the FPI method. The first is the use of importance functions for dihedral angles between sets of generalized Jacobi coordinate vectors. The second is an extension of our stratification scheme to allow some strata to be defined based only on coordinate information while other strata are defined based on both the geometry and the energy of the centroid of the Feynman path. These enhanced methods are applied to calculate converged partition functions by FPI methods, and these results are compared to ones obtained earlier by vibrational configuration interaction (VCI) calculations, both calculations being for the JordanGilbert potential energy surface. The earlier VCI calculations are found to agree well (within ?1.5%) with the new benchmarks. The FPI partition functions presented here are estimated to be converged to within a 2? statistical uncertainty of between 0.04% and 0.07% for the given potential energy surface for temperatures in the range 3003000 K and are the most accurately converged partition functions for a given potential energy surface for any molecule with five or more atoms. We also tabulate free energies, enthalpies, entropies, and heat capacities.
NASA Astrophysics Data System (ADS)
Mielke, Steven L.; Truhlar, Donald G.
2015-01-01
We present an improved version of our "path-by-path" enhanced same path extrapolation scheme for Feynman path integral (FPI) calculations that permits rapid convergence with discretization errors ranging from O(P-6) to O(P-12), where P is the number of path discretization points. We also present two extensions of our importance sampling and stratified sampling schemes for calculating vibrational-rotational partition functions by the FPI method. The first is the use of importance functions for dihedral angles between sets of generalized Jacobi coordinate vectors. The second is an extension of our stratification scheme to allow some strata to be defined based only on coordinate information while other strata are defined based on both the geometry and the energy of the centroid of the Feynman path. These enhanced methods are applied to calculate converged partition functions by FPI methods, and these results are compared to ones obtained earlier by vibrational configuration interaction (VCI) calculations, both calculations being for the Jordan-Gilbert potential energy surface. The earlier VCI calculations are found to agree well (within 1.5%) with the new benchmarks. The FPI partition functions presented here are estimated to be converged to within a 2? statistical uncertainty of between 0.04% and 0.07% for the given potential energy surface for temperatures in the range 300-3000 K and are the most accurately converged partition functions for a given potential energy surface for any molecule with five or more atoms. We also tabulate free energies, enthalpies, entropies, and heat capacities.
Mielke, Steven L; Truhlar, Donald G
2015-01-28
We present an improved version of our "path-by-path" enhanced same path extrapolation scheme for Feynman path integral (FPI) calculations that permits rapid convergence with discretization errors ranging from O(P(-6)) to O(P(-12)), where P is the number of path discretization points. We also present two extensions of our importance sampling and stratified sampling schemes for calculating vibrational-rotational partition functions by the FPI method. The first is the use of importance functions for dihedral angles between sets of generalized Jacobi coordinate vectors. The second is an extension of our stratification scheme to allow some strata to be defined based only on coordinate information while other strata are defined based on both the geometry and the energy of the centroid of the Feynman path. These enhanced methods are applied to calculate converged partition functions by FPI methods, and these results are compared to ones obtained earlier by vibrational configuration interaction (VCI) calculations, both calculations being for the Jordan-Gilbert potential energy surface. The earlier VCI calculations are found to agree well (within ?1.5%) with the new benchmarks. The FPI partition functions presented here are estimated to be converged to within a 2? statistical uncertainty of between 0.04% and 0.07% for the given potential energy surface for temperatures in the range 300-3000 K and are the most accurately converged partition functions for a given potential energy surface for any molecule with five or more atoms. We also tabulate free energies, enthalpies, entropies, and heat capacities. PMID:25637967
NASA Astrophysics Data System (ADS)
Toy, Mehmet; Tanak, Hasan
2016-01-01
In the present work, a combined experimental and theoretical study on ground state molecular structure, spectroscopic and nonlinear optical properties of azo compound 3?-chloro-4-dimethlamino azobenzene are reported. The molecular geometry, vibrational wavenumbers and the first order hyperpolarizability of the title compound were calculated with the help of density functional theory computations. The optimized geometric parameters obtained by using DFT (B3LYP/6-311++G(d,p)) show good agreement with the experimental data. The vibrational transitions were identified based on the recorded FT-IR spectra in the range of 4000-400 cm-1 for solid state. The 1H isotropic chemical shifts with respect to TMS were also calculated using the gauge independent atomic orbital (GIAO) method and compared with the experimental data. Using the TD-DFT method, electronic absorption spectra of the title compound have been predicted, and good agreement is determined with the experimental ones. To investigate the NLO properties of the title compound, the polarizability and the first hyperpolarizability were calculated using the density functional B3LYP method with the 6-311++G(d,p) basis set. According to results, the title compound exhibits non-zero first hyperpolarizability value revealing second order NLO behavior. In addition, DFT calculations of the title compound, molecular electrostatic potential and frontier molecular orbitals were also performed at 6-311++G(d,p) level of theory.
Toy, Mehmet; Tanak, Hasan
2016-01-01
In the present work, a combined experimental and theoretical study on ground state molecular structure, spectroscopic and nonlinear optical properties of azo compound 3'-chloro-4-dimethlamino azobenzene are reported. The molecular geometry, vibrational wavenumbers and the first order hyperpolarizability of the title compound were calculated with the help of density functional theory computations. The optimized geometric parameters obtained by using DFT (B3LYP/6-311++G(d,p)) show good agreement with the experimental data. The vibrational transitions were identified based on the recorded FT-IR spectra in the range of 4000-400cm(-1) for solid state. The (1)H isotropic chemical shifts with respect to TMS were also calculated using the gauge independent atomic orbital (GIAO) method and compared with the experimental data. Using the TD-DFT method, electronic absorption spectra of the title compound have been predicted, and good agreement is determined with the experimental ones. To investigate the NLO properties of the title compound, the polarizability and the first hyperpolarizability were calculated using the density functional B3LYP method with the 6-311++G(d,p) basis set. According to results, the title compound exhibits non-zero first hyperpolarizability value revealing second order NLO behavior. In addition, DFT calculations of the title compound, molecular electrostatic potential and frontier molecular orbitals were also performed at 6-311++G(d,p) level of theory. PMID:25468435
NASA Astrophysics Data System (ADS)
Guirgis, Gamil A.; Zheng, Chao; Nashed, Yasser E.; Mohamed, Tarek A.; Durig, James R.
2003-04-01
Infrared spectra (3500-50 cm -1) of gaseous and solid and Raman spectra (3500-30 cm -1) of liquid and solid dichloromethyldimethyl silane, CHCl 2Si(CH 3) 2H, are reported. Additionally, the depolarization measurements have been obtained from the Raman spectrum of the liquid. The gauche and anti rotamers have been identified in the fluid phases but only the gauche conformer remains in the polycrystalline solid. From temperature dependent FT-infrared spectra of krypton solutions, it is shown that the gauche conformer is more stable than the anti form by 126±13 cm -1 (1.51±0.16 kJ mol -1). At ambient temperature there is 21±2% of the anti conformer present. Complete vibrational assignments are provided for the gauche conformer and several modes are identified for the anti form. Harmonic force constants, fundamental frequencies, infrared intensities, and Raman activities have been obtained from MP2/6-31G(d) calculations with full electron correlation. The optimized geometries and conformational stabilities have also been obtained from ab initio MP2/6-31G(d), MP2/6-311+G(d,p) and MP2/6-311+G(2d,2p) calculations with full electron correlation. The r0 SiH bond distances of 1.482 and 1.485 Å have been obtained for the anti and gauche conformers, respectively, from the silicon-hydrogen stretching frequencies. These results are compared to the corresponding quantities of some similar molecules.
Tabulation of hybrid theory calculated e-N2 vibrational and rotational cross sections
NASA Technical Reports Server (NTRS)
Chandra, N.; Temkin, A.
1976-01-01
Vibrational excitation cross sections of N2 by electron impact are tabulated. Integrated cross sections are given for transitions v yields v prime where o=or v=or 8 in the energy range 0.1 eV=or E=or 10 eV. The energy grid is chosen to be most dense in the resonance region (2 to 4 eV) so that the substructure is present in the numerical results. Coefficients in the angular distribution formula (differential scattering cross section) for transitions v=0 yields v prime = or 8 are also numerically given over the same grid of energies. Simultaneous rotation-vibration coefficients are also given for transitions v=o,j=o; 1 yields v prime=o, j=o,2,4; 1,3,5. All results are obtained from the hybrid theory.
NASA Astrophysics Data System (ADS)
Valds, lvaro; Prosmiti, Rita; Delgado-Barrio, Gerardo
2012-12-01
Full-dimensional multiconfiguration time-dependent Hartree (MCTDH) computations are reported for the vibrational states of the H_5^+ and its H4D+, H3D_2^+, H2D_3^+, HD_4^+, D_5^+ isotopologues employing two recent analytical potential energy surfaces of Xie et al. [J. Chem. Phys. 122, 224307 (2005), 10.1063/1.1927529] and Aguado et al. [J. Chem. Phys. 133, 024306 (2010), 10.1063/1.3454658]. The potential energy operators are constructed using the n-mode representation adapted to a four-combined mode cluster expansion, including up to seven-dimensional grids, chosen adequately to take advantage in representing the MCTDH wavefunction. An error analysis is performed to quantify the convergence of the potential expansion to reproduce the reference surfaces at the energies of interest. An extensive analysis of the vibrational ground state properties of these isotopes and comparison with the reference diffusion Monte Carlo results by Acioli et al. [J. Chem. Phys. 128, 104318 (2008), 10.1063/1.2838847] are presented. It is found that these systems are highly delocalized, interconverting between equivalent minima through rotation and internal proton transfer motions even at their vibrational ground state. Isotopic substitution affects the zero-point energy and structure, showing preference in the arrangements of the H and D within the mixed clusters, and the most stable conformers of each isotopomer are the ones with the H in the central position. Vibrational excited states are also computed and by comparing the energies and structures predicted from the two surfaces, the effect of the potential topology on them is discussed.
Czak, Gbor; Furtenbacher, Tibor; Barletta, Paolo; Csszr, Attila G; Szalay, Viktor; Sutcliffe, Brian T
2007-07-14
A technique has been developed which in principle allows the determination of the full rotational-vibrational eigenspectrum of triatomic molecules by treating the important singularities present in the triatomic rotational-vibrational kinetic energy operator given in Jacobi coordinates and the R(1) embedding. The singular term related to the diatom-type coordinate, R(1), deemed to be unimportant for spectroscopic applications, is given no special attention. The work extends a previous [J. Chem. Phys., 2005, 122, 024101] vibration-only approach and employs a generalized finite basis representation (GFBR) resulting in a nonsymmetric Hamiltonian matrix [J. Chem. Phys., 2006, 124, 014110]. The basis set to be used is obtained by taking the direct product of a 1-D DVR basis, related to R(1), with a 5-D nondirect-product basis, the latter formed by coupling Bessel-DVR functions depending on the distance-type coordinate causing the singularity, associated Legendre polynomials depending on the Jacobi angle, and rotational functions depending on the three Euler angles. The robust implicitly restarted Arnoldi method within the ARPACK package is used for the determination of a number of eigenvalues of the nonsymmetric Hamiltonian matrix. The suitability of the proposed approach is shown by the determination of the rotational-vibrational energy levels of the ground electronic state of H(3)(+) somewhat above its barrier to linearity. Convergence of the eigenenergies is checked by an alternative approach, employing a Hamiltonian expressed in Radau coordinates, a standard direct-product basis, and no treatment of the singularities. PMID:17664964
Ab initio calculation of the ro-vibrational spectrum of H2F+
NASA Astrophysics Data System (ADS)
Kyuberis, Aleksandra A.; Lodi, Lorenzo; Zobov, Nikolai F.; Polyansky, Oleg L.
2015-10-01
An ab initio study of the rotation-vibrational spectrum of the electronic ground state of the (gas-phase) fluoronium ion H2F+ is presented. A new potential energy surface (PES) and a new dipole moment surface (DMS) were produced and used to compute rotation-vibrational energy levels, line positions and line intensities. Our computations achieve an accuracy of 0.15 cm-1 for the fundamental vibrational frequencies, which is about 50 times more accurate than previous ab initio results. The computed room-temperature line list should facilitate the experimental observations of new H2F+ lines, in particular of yet unobserved overtone transitions. The H2F+ molecular ion, which is isoelectronic to water, has a non-linear equilibrium geometry but a low-energy barrier to linearity at about 6000 cm-1. As a result the effects of so-called quantum monodromy become apparent already at low bending excitations. An analysis of excited bends in terms of quantum monodromy is presented.
NASA Astrophysics Data System (ADS)
Bubin, Sergiy; Stanke, Monika; Adamowicz, Ludwik
2011-04-01
All 18 bound pure vibrational levels of the HD molecule have been calculated within the framework that does not assume the Born-Oppenheimer (BO) approximation. The nonrelativistic energies of the states have been corrected for the relativistic effects of the order of ?2 (where ? is the fine structure constant), calculated using the perturbation theory with the nonrelativistic non-BO wave functions being the zero-order approximation. The calculations were performed by expanding the non-BO wave functions in terms of one-center explicitly correlated Gaussian functions multiplied by even powers of the internuclear distance and by performing extensive optimization of the Gaussian nonlinear parameters. Up to 10 000 basis functions were used for each state.
Petrenko, T.; George, S.D.; Aliaga-Alcalde, N.; Bill, E.; Mienert, B.; Xiao, Y.; Guo, Y.; Sturhahn, W.; Cramer, S.P.; Wieghardt, K.; Neese, F.; /Bonn U., LTC /SLAC, SSRL /Max Planck Inst., Mulheim /UC, Davis /Argonne /LBL, Berkeley
2007-10-19
The characterization of high-valent iron species is of interest due to their relevance to biological reaction mechanisms. Recently, we have synthesized and characterized an [Fe(V)-nitrido-cyclam-acetato]+ complex, which has been characterized by M{umlt o}ssbauer, magnetic susceptibility data, and XAS spectroscopies combined with DFT calculations. The results of this study indicated that the [Fe(V)-nitrido-cyclam-acetato]+ complex is an unusual d3 system with a nearly orbitally degenerate S = 1/2 ground state. Although the calculations predicted fairly different Fe-N stretching frequencies for the S = 1/2 and the competing S = 3/2 ground states, a direct experimental determination of this important fingerprint quantity was missing. Here we apply synchrotron-based nuclear resonance vibrational scattering (NRVS) to characterize the Fe-N stretching frequency of an Fe(V)-nitrido complex and its Fe(III)-azide precursor. The NRVS data show a new isolated band at 864 cm-1 in the Fe(V)-nitrido complex that is absent in the precursor. The NRVS spectra are fit and simulated using a DFT approach, and the new feature is unambiguously assigned to a Fe(V)-N stretch. The calculated Fe-N stretching frequency is too high by {approx}75 cm-1. Anharmonic contributions to the Fe-N stretching frequency have been evaluated and have been found to be small (-5.5 cm-1). The NRVS data provided a unique opportunity to obtain this vibrational information, which had eluded characterization by more traditional vibrational spectroscopies.
Yu, Hua-Gen
2015-01-28
We report a rigorous full dimensional quantum dynamics algorithm, the multi-layer Lanczos method, for computing vibrational energies and dipole transition intensities of polyatomic molecules without any dynamics approximation. The multi-layer Lanczos method is developed by using a few advanced techniques including the guided spectral transform Lanczos method, multi-layer Lanczos iteration approach, recursive residue generation method, and dipole-wavefunction contraction. The quantum molecular Hamiltonian at the total angular momentum J = 0 is represented in a set of orthogonal polyspherical coordinates so that the large amplitude motions of vibrations are naturally described. In particular, the algorithm is general and problem-independent. An application is illustrated by calculating the infrared vibrational dipole transition spectrum of CH4 based on the ab initio T8 potential energy surface of Schwenke and Partridge [Spectrochimica Acta, Part A 57, 887 (2001)] and the low-order truncated ab initio dipole moment surfaces of Yurchenko et al. [J. Mol. Spectrosc. 291, 69 (2013)]. A comparison with experiments is made. The algorithm is also applicable for Raman polarizability active spectra. PMID:25637968
Yu, Hua-Gen
2015-01-28
We report a rigorous full dimensional quantum dynamics algorithm, the multi-layer Lanczos method, for computing vibrational energies and dipole transition intensities of polyatomic molecules without any dynamics approximation. The multi-layer Lanczos method is developed by using a few advanced techniques including the guided spectral transform Lanczos method, multi-layer Lanczos iteration approach, recursive residue generation method, and dipole-wavefunction contraction. The quantum molecular Hamiltonian at the total angular momentum J = 0 is represented in a set of orthogonal polyspherical coordinates so that the large amplitude motions of vibrations are naturally described. In particular, the algorithm is general and problem-independent. An application is illustrated by calculating the infrared vibrational dipole transition spectrum of CH₄ based on the ab initio T8 potential energy surface of Schwenke and Partridge and the low-order truncated ab initio dipole moment surfaces of Yurchenko and co-workers. A comparison with experiments is made. The algorithm is also applicable for Raman polarizability active spectra.
Yu, Hua-Gen
2015-01-28
We report a rigorous full dimensional quantum dynamics algorithm, the multi-layer Lanczos method, for computing vibrational energies and dipole transition intensities of polyatomic molecules without any dynamics approximation. The multi-layer Lanczos method is developed by using a few advanced techniques including the guided spectral transform Lanczos method, multi-layer Lanczos iteration approach, recursive residue generation method, and dipole-wavefunction contraction. The quantum molecular Hamiltonian at the total angular momentum J = 0 is represented in a set of orthogonal polyspherical coordinates so that the large amplitude motions of vibrations are naturally described. In particular, the algorithm is general and problem-independent. An applicationmore » is illustrated by calculating the infrared vibrational dipole transition spectrum of CH₄ based on the ab initio T8 potential energy surface of Schwenke and Partridge and the low-order truncated ab initio dipole moment surfaces of Yurchenko and co-workers. A comparison with experiments is made. The algorithm is also applicable for Raman polarizability active spectra.« less
Yu, Hua-Gen
2015-01-28
We report a rigorous full dimensional quantum dynamics algorithm, the multi-layer Lanczos method, for computing vibrational energies and dipole transition intensities of polyatomic molecules without any dynamics approximation. The multi-layer Lanczos method is developed by using a few advanced techniques including the guided spectral transform Lanczos method, multi-layer Lanczos iteration approach, recursive residue generation method, and dipole-wavefunction contraction. The quantum molecular Hamiltonian at the total angular momentum J = 0 is represented in a set of orthogonal polyspherical coordinates so that the large amplitude motions of vibrations are naturally described. In particular, the algorithm is general and problem-independent. An application is illustrated by calculating the infrared vibrational dipole transition spectrum of CH{sub 4} based on the ab initio T8 potential energy surface of Schwenke and Partridge [Spectrochimica Acta, Part A 57, 887 (2001)] and the low-order truncated ab initio dipole moment surfaces of Yurchenko et al. [J. Mol. Spectrosc. 291, 69 (2013)]. A comparison with experiments is made. The algorithm is also applicable for Raman polarizability active spectra.
Yu, Hua-Gen
2015-01-28
We report a rigorous full dimensional quantum dynamics algorithm, the multi-layer Lanczos method, for computing vibrational energies and dipole transition intensities of polyatomic molecules without any dynamics approximation. The multi-layer Lanczos method is developed by using a few advanced techniques including the guided spectral transform Lanczos method, multi-layer Lanczos iteration approach, recursive residue generation method, and dipole-wavefunction contraction. The quantum molecular Hamiltonian at the total angular momentum J = 0 is represented in a set of orthogonal polyspherical coordinates so that the large amplitude motions of vibrations are naturally described. In particular, the algorithm is general and problem-independent. An application is illustrated by calculating the infrared vibrational dipole transition spectrum of CH? based on the ab initio T8 potential energy surface of Schwenke and Partridge and the low-order truncated ab initio dipole moment surfaces of Yurchenko and co-workers. A comparison with experiments is made. The algorithm is also applicable for Raman polarizability active spectra.
Skokov, S.; Peterson, K.A.; Bowman, J.M.
1998-08-01
Accurate {ital ab initio} multireference configuration interaction (CI) calculations with large correlation-consistent basis sets are performed for HOCl. After extrapolation to the complete basis set limit, the {ital ab initio} data are precisely fit to give a semiglobal three-dimensional potential energy surface to describe HOCl{r_arrow}Cl+OH from high overtone excitation of the OH-stretch. The average absolute deviation between the {ital ab initio} and fitted energies is 4.2thinspcm{sup {minus}1} for energies up to 60 kcal/mol relative to the HOCl minimum. Vibrational energies of HOCl including the six overtones of the OH-stretch are computed using a vibrational-Cl method on the fitted potential and also on a slightly adjusted potential. Near-spectroscopic accuracy is obtained using the adjusted potential; the average absolute deviation between theory and experiment for 19 experimentally reported states is 4.8thinspcm{sup {minus}1}. Very good agreement with experiment is also obtained for numerous rotational energies for the ground vibrational state, the ClO-stretch fundamental, and the fifth overtone of the OH-stretch. {copyright} {ital 1998 American Institute of Physics.}
Singh, Swapnil; Singh, Harshita; Srivastava, Anubha; Tandon, Poonam; Sinha, Kirti; Bharti, Purnima; Kumar, Sudhir; Kumar, Padam; Maurya, Rakesh
2014-11-11
In the present work, a detailed conformational study of cladrin (3-(3,4-dimethoxy phenyl)-7-hydroxychromen-4-one) has been done by using spectroscopic techniques (FT-IR/FT-Raman/UV-Vis/NMR) and quantum chemical calculations. The optimized geometry, wavenumber and intensity of the vibrational bands of the cladrin in ground state were calculated by density functional theory (DFT) employing 6-311++G(d,p) basis sets. The study has been focused on the two most stable conformers that are selected after the full geometry optimization of the molecule. A detailed assignment of the FT-IR and FT-Raman spectra has been done for both the conformers along with potential energy distribution for each vibrational mode. The observed and scaled wavenumber of most of the bands has been found to be in good agreement. The UV-Vis spectrum has been recorded and compared with calculated spectrum. In addition, 1H and 13C nuclear magnetic resonance spectra have been also recorded and compared with the calculated data that shows the inter or intramolecular hydrogen bonding. The electronic properties such as HOMO-LUMO energies were calculated by using time-dependent density functional theory. Molecular electrostatic potential has been plotted to elucidate the reactive part of the molecule. Natural bond orbital analysis was performed to investigate the molecular stability. Non linear optical property of the molecule have been studied by calculating the electric dipole moment (μ) and the first hyperpolarizability (β) that results in the nonlinearity of the molecule. PMID:24892542
NASA Astrophysics Data System (ADS)
Afifi, Mahmoud S.; Farag, Rabei S.; Shaaban, Ibrahim A.; Wilson, Lee D.; Zoghaib, Wajdi M.; Mohamed, Tarek A.
2013-07-01
The infrared (4000-200 cm-1) spectrum for 4-amino-5-pyrimidinecarbonitrile (APC, C5H4N4) was acquired in the solid phase. In addition, the 1H and 13C NMR spectra of APC were obtained in DMSO-d6 along with its mass spectrum. Initially, six isomers were hypothesized and then investigated by means of DFT/B3LYP and MP2(full) quantum mechanical calculations using a 6-31G(d) basis set. Moreover, the 1H and 13C NMR chemical shifts were predicted using a GIAO approximation at the 6-311+G(d,p) basis set and the B3LYP method with (and without) solvent effects using PCM method. The correlation coefficients showed good agreement between the experimental/theoretical chemical shift values of amino tautomers (1 and 2) rather than the eliminated imino tautomers (3-6), in agreement with the current quantum mechanical calculations. Structures 3-6 are less stable than the amino tautomers (1 and 2) by about 5206-8673 cm-1 (62.3-103.7 kJ/mol). The MP2(full)/6-31G(d) computational results favor the amino structure 1 with a pyramidal NH2 moiety and calculated real vibrational frequencies, however; structure 2 is considered a transition state owing to the calculated imaginary frequency. It is worth mentioning that, the calculated structural parameters suggest a strong conjugation between the amino nitrogen and pyrimidine ring. Aided by frequency calculations, normal coordinate analysis, force constants and potential energy distributions (PEDs), a complete vibrational assignment for the observed bands is proposed herein. Finally, NH2 internal rotation barriers for the stable non-planar isomer (1) were carried out using MP2(full)/6-31G(d) optimized structural parameters. Our results are discussed herein and compared to structural parameters for similar molecules whenever appropriate.
Elleuch, S; Feki, H; Abid, Y
2007-11-01
The conformational stability and vibrational modes of the N-diethylendiamine organic cation (N-DD(2+)) were studied by experimental (Raman) spectroscopy combined with theoretical calculations. Various ab initio theories were used: Hartree-Fock (HF) theory, Mller-Plesset second-order perturbation (MP2) theory and density functional theory (DFT). Three stable conformers of N-DD(2+), trans-trans, gauche-gauche and gauche-trans were calculated. A comparison between the computed structural parameters of the conformers at both levels of theory and the X-ray data was made. It is demonstrated that the N-DD(2+) cation adopts more probably the gauche-gauche conformation at room temperature. In order to make a more detailed interpretation of the low temperature phase transition of N-DDHP, the Raman spectra of N-DDHP were recorded at room and low temperature in the 200-3400 cm(-1) region. The vibrational frequencies of the different conformers of N-DD(2+) were also calculated using the DFT/B3LYP (6-31G(d)) level of theory. By comparison between the experimental and theoretical results, the conformational dynamic of the N-DD(2+) organic cation was confirmed. It is shown that the N-DD(2+) cation configuration changes from gauche-gauche conformer to gauche-trans conformer when decreasing the temperature. PMID:17317286
Baklouti, Yosra; chaari, Najla; Feki, Habib; Chniba-Boudjada, Nassira; Zouari, Fatma
2015-02-01
Single crystals of a new organic-inorganic compound (C9H24N2) CdCl4 were grown by the slow evaporation technique and characterized by X-ray diffraction, infrared absorption Raman spectroscopy scattering, optical absorption, differential scanning calorimetry (DSC) analysis and dielectric measurements. The title compound belongs to the orthorhombic space group Pbca with the following unit cell parameters: a=11.397(7), b=13.843(4), c=22.678(5)Å and Z=8. In crystal structure, the tetrachlorocadmate anion is connected to organic cations through N-H⋯Cl hydrogen bonds. Theoretical calculations were performed using density functional theory (DFT) with the B3LYP/LanL2DZ level of theory for studying the molecular structure and vibrational spectra of the title compound. Good consistency is found between the calculated results and the experimental structure, IR, and Raman spectra. The detailed interpretation of the vibrational modes was carried out on the basis on our DFT calculations as primary source of assignment and by comparison with spectroscopic studies of similar compounds. The optical properties were investigated by optical absorption and show three bands at 300, 329 and 513 nm. PMID:25311521
Lebedieva, Tetiana; Gubanov, Victor; Dovbeshko, Galyna; Pidhirnyi, Denys
2015-12-01
Different notations of graphene irreducible representations and optical modes could be found in the literature. The goals of this paper are to identify the correspondence between available notations, to calculate the optical modes of graphene in different points of the Brillouin zone, and to compare them with experimental data obtained by Raman and coherent anti-Stokes Raman scattering (CARS) spectroscopy. The mechanism of the resonance enhancement of vibration modes of the molecules adsorbed on graphene in CARS experiments is proposed. The possibility of appearance of the discrete breathing modes is discussed. PMID:26168865
NASA Astrophysics Data System (ADS)
Xie, Congwei; Zeng, Qingfeng; Dong, Dong; Gao, Shuang; Cai, Yongqing; Oganov, Artem R.
2014-05-01
First-principles calculations have been conducted to study the structural, dielectric, and vibrational properties of ferroelectric and paraelectric BaAl2O4. High-frequency and static dielectric constants, and phonon frequencies at the Brillouin zone center are reported. Both BaAl2O4 polymorphs are promising infrared-transparent materials due to their low electronic dielectric constants. The ferroelectric and paraelectric BaAl2O4 have much smaller permittivity compared to the classical ferroelectric materials. From an atomic nanostructure standpoint, the abnormally low permittivity of BaAl2O4 polymorphs is mainly related to low coordination numbers of Ba (9) and Al (4).
NASA Astrophysics Data System (ADS)
Lebedieva, Tetiana; Gubanov, Victor; Dovbeshko, Galyna; Pidhirnyi, Denys
2015-07-01
Different notations of graphene irreducible representations and optical modes could be found in the literature. The goals of this paper are to identify the correspondence between available notations, to calculate the optical modes of graphene in different points of the Brillouin zone, and to compare them with experimental data obtained by Raman and coherent anti-Stokes Raman scattering (CARS) spectroscopy. The mechanism of the resonance enhancement of vibration modes of the molecules adsorbed on graphene in CARS experiments is proposed. The possibility of appearance of the discrete breathing modes is discussed.
Meninno, Sara; Rizzo, Paola; Abbate, Sergio; Longhi, Giovanna; Mazzeo, Giuseppe; Monaco, Guglielmo; Lattanzi, Alessandra; Zanasi, Riccardo
2016-02-01
Density functional theory calculation of the vibrational circular dichroism spectrum was used to assign the absolute configuration of an all-carbon quaternary ?-stereocenter of a ?-butyrolactone recently synthesized through an asymmetric organocatalytic tandem aldol/lactonization sequence. Comparison with the experimental spectrum is satisfactory, on account of the fact that spectroscopic features are weak due to the presence of multiple conformers. As a result, the (R) absolute configuration was assigned to the (+) optical isomer. Chirality 28:110-115, 2016. 2015 Wiley Periodicals, Inc. PMID:26634798
NASA Technical Reports Server (NTRS)
Bauschlicher, Charles W.; Arnold, James O. (Technical Monitor)
1997-01-01
The vibrational frequencies of MO2 are computed at many levels of theory, including HF, B3LYP, BP86, CASSCF, MP2, and CCSD(T). The computed results are compared with the available experimental results. Most of the methods fail for at least one state of the systems considered. The accuracy of the results and the origin of the observed failures are discussed. The B3LYP bond energies are compared with traditional methods for a variety of systems, ranging from FeCOn+ to SiCln and its positive ions. The cases where B3LYP differs from the traditional methods are discussed.
NASA Astrophysics Data System (ADS)
Saja, D.; Joe, I. Hubert; Jayakumar, V. S.
2006-01-01
The NIR-FT Raman, FT-IR spectral analysis of potential NLO material P-Amino Acetanilide is carried out by density functional computations. The optimized geometry shows that NH2 and NHCOCH3 groups substituted in para position of phenyl ring are non-planar which predicts maximum conjugation of molecule with donor and acceptor groups. Vibrational analysis reveals that simultaneous IR and Raman activation of the phenyl ring modes also provide evidence for the charge transfer interaction between the donors and the acceptor can make the molecule highly polarized and the intra molecular charge transfer interaction must be responsible for the NLO properties of PAA.
Balachandran, V; Rajeswari, S; Lalitha, S
2013-09-01
In this work, FT-IR and FT-Raman spectra are recorded on the solid phase of 5-nitro-2-furoic acid (abbreviated as NFA) in the regions 4000-400 cm(-1) and 3500-100 cm(-1) respectively. The geometrical parameters, vibrational assignments, HOMO-LUMO energies and NBO calculations are obtained for the monomer and dimer of NFA from HF and DFT (B3LYP) with 6-311++G (d, p) basis set calculations. Second order perturbation energies and electron density (ED) transfer from filled lone pairs of Lewis base to unfilled Lewis acid sites of NFA are discussed on the basis of NBO analysis. Intermolecular hydrogen bonds exist through COOH groups; give the evidence for the formation of dimer entities in the title molecule. The theoretically calculated harmonic frequencies are scaled by common scale factor. The observed and the calculated frequencies are found to be in good agreement. The thermodynamic functions were obtained for the range of temperature 100-1000 K. The polarizability, first hyperpolarizability, anisotropy polarizability invariant has been computed using quantum chemical calculations. The chemical parameters were calculated from the HOMO and LUMO values. The NMR chemical shielding anisotropy (CSA) parameters were also computed for the title molecule. PMID:23735205
Kostadinova, O.; Chrissanthopoulos, A.; Petkova, T.; Petkov, P.; Yannopoulos, S.N.
2011-02-15
We report an investigation of the structure and vibrational modes of (AgI){sub x} (AsSe){sub 100-x}, bulk glasses using Raman spectroscopy and first principles calculations. The short- and medium-range structural order of the glasses was elucidated by analyzing the reduced Raman spectra, recorded at off-resonance conditions. Three distinct local environments were revealed for the AsSe glass including stoichiometric-like and As-rich network sub-structures, and cage-like molecules (As{sub 4}Se{sub n}, n=3, 4) decoupled from the network. To facilitate the interpretation of the Raman spectra ab initio calculations are employed to study the geometric and vibrational properties of As{sub 4}Se{sub n} molecular units that are parts of the glass structure. The incorporation of AgI causes appreciable structural changes into the glass structure. AgI is responsible for the population reduction of molecular units and for the degradation of the As-rich network-like sub-structure via the introduction of As-I terminal bonds. Ab initio calculations of mixed chalcohalide pyramids AsSe{sub m}I{sub 3-m} provided useful information augmenting the interpretation of the Raman spectra. -- Graphical abstract: Raman scattering and ab initio calculations are employed to study the structure of AgI-AsSe superionic glasses. The role of mixed chalcohalide pyramidal units as illustrated in the figure is elucidated. Display Omitted Research highlights: {yields} Doping binary As-Se glasses with AgI cause dramatic changes in glass structure. {yields} Raman scattering and ab initio calculations determine changes in short- and medium-range order. {yields} Three local environments exist in AsSe glass including a network sub-structure and cage-like molecules. {yields} Mixed chalcohalide pyramids AsSe{sub m}I{sub 3-m} dominate the AgI-doped glass structure.
Voids at the tunnel-soil interface for calculation of ground vibration from underground railways
NASA Astrophysics Data System (ADS)
Jones, Simon; Hunt, Hugh
2011-01-01
Voids at the tunnel-soil interface are not normally considered when predicting ground vibration from underground railways. The soil is generally assumed to be continuously bonded to the outer surface of the tunnel to simplify the modelling process. Evidence of voids around underground railways motivated the study presented herein to quantify the level of uncertainty in ground vibration predictions associated with neglecting to include such voids at the tunnel-soil interface. A semi-analytical method is developed which derives discrete transfers for the coupled tunnel-soil model based on the continuous Pipe-in-Pipe method. The void is simulated by uncoupling the appropriate nodes at the interface to prevent force transfer between the systems. The results from this investigation show that relatively small voids ( 4 m90?) can significantly affect the rms velocity predictions in the near-field and moderately affect predictions in the far-field. Sensitivity of the predictions to void length and void sector angle are both deemed to be significant. The findings from this study suggest that the uncertainty associated with assuming a perfect bond at the tunnel-soil interface in an area with known voidage can reasonably reach 5 dB and thus should be considered in the design process.
Calculation of the harmonic spectrum for one and two-electron atoms in two-colour laser fields
NASA Astrophysics Data System (ADS)
Robinson, D. J.; Parker, J. S.; Moore, L. R.; Taylor, K. T.
2012-11-01
We study the behaviour of hydrogen and helium atoms in intense two-colour linearly-polarised laser fields. Two cases are considered - the case where both fields act with parallel axes of polarisation and the case where the polarisation axes are perpendicular. We report extensions of the HELIUM code and a related hydrogen code to study these two cases of the two-colour problem. The impact of the second laser pulse on the harmonic spectrum is explored.
NASA Technical Reports Server (NTRS)
Schwenke, David W.; Langhoff, Stephen R. (Technical Monitor)
1995-01-01
A description is given of an algorithm for computing ro-vibrational energy levels for tetratomic molecules. The expressions required for evaluating transition intensities are also given. The variational principle is used to determine the energy levels and the kinetic energy operator is simple and evaluated exactly. The computational procedure is split up into the determination of one dimensional radial basis functions, the computation of a contracted rotational-bending basis, followed by a final variational step coupling all degrees of freedom. An angular basis is proposed whereby the rotational-bending contraction takes place in three steps. Angular matrix elements of the potential are evaluated by expansion in terms of a suitable basis and the angular integrals are given in a factorized form which simplifies their evaluation. The basis functions in the final variational step have the full permutation symmetries of the identical particles. Sample results are given for HCCH and BH3.
Sun, Shou -Tian; Jiang, Ling; Liu, J. W.; Heine, Nadja; Yacovitch, Tara I.; Wende, Torsten; Asmis, Knut R.; Neumark, Daniel M.; Liu, Zhi -Feng
2015-06-05
We report infrared multiple photon dissociation (IRMPD) spectra of cryogenically-cooled H2PO4-(H2O)n anions (n = 2–12) in the spectral range of the stretching and bending modes of the solute anion (600–1800 cm-1). The spectra cannot be fully understood using the standard technique of comparison to harmonic spectra of minimum-energy structures; a satisfactory assignment requires considering anharmonic effects as well as entropy-driven hydrogen bond network fluctuations. Aided by finite temperature ab initio molecular dynamics simulations, the observed changes in the position, width and intensity of the IRMPD bands with cluster size are related to the sequence of microsolvation. Due to stronger hydrogenmore » bonding to the two terminal P=O groups, these are hydrated before the two P–OH groups. By n = 6, all four end groups are involved in the hydrogen bond network and by n = 12, the cluster spectra show similarities to the condensed phase spectrum of H2PO4-(aq). Our results reveal some of the microscopic details concerning the formation of the aqueous solvation environment around H2PO4-, provide ample testing grounds for the design of model solvation potentials for this biologically relevant anion, and support a new paradigm for the interpretation of IRMPD spectra of microhydrated ions.« less
NASA Astrophysics Data System (ADS)
Berger, C. E.; Anderson, E. R.; Drut, J. E.
2015-05-01
We determine the ground-state energy and Tan's contact of attractively interacting few-fermion systems in a one-dimensional harmonic trap, for a range of couplings and particle numbers. Complementing those results, we show the corresponding density profiles. The calculations were performed with a lattice Monte Carlo approach based on a nonuniform discretization of space, defined via Gauss-Hermite quadrature points and weights. This particular coordinate basis is natural for systems in harmonic traps, and can be generalized to traps of other shapes. In all cases, it yields a position-dependent coupling and a corresponding nonuniform Hubbard-Stratonovich transformation. The resulting path integral is performed with hybrid Monte Carlo as a proof of principle for calculations at finite temperature and in higher dimensions. We present results for N =4 ,...,20 particles (although the method can be extended beyond that) to cover the range from few- to many-particle systems. This method is exact up to statistical and systematic uncertainties, which we account for—and thus also represents an ab initio calculation of this system, providing a benchmark for other methods and a prediction for ultracold-atom experiments.
Oschetzki, Dominik; Rauhut, Guntram
2014-08-21
The vibrational spectra of a series of small lithium fluoride clusters, i.e. (LiF)n, n = 2-10, were studied by vibrational configuration interaction (VCI) calculations relying on potential energy surfaces including three-mode coupling terms and being obtained from explicitly correlated local coupled cluster calculations. Due to the account for anharmonicity effects, the simulated spectra allow for a direct comparison with experimental data and may thus help to identify clusters in the experiments. Even structurally closely related clusters can clearly be distinguished by infrared spectroscopy. The largest system in this study required more than 1000 basis functions in the electronic structure calculations and more than 10(7) configurations in the vibrational structure calculations and became computationally feasible only due to a combination of different approximations and highly parallelized algorithms. PMID:24981078
NASA Astrophysics Data System (ADS)
Rajesh, P.; Gunasekaran, S.; Gnanasambandan, T.; Seshadri, S.
2015-02-01
The complete vibrational assignment and analysis of the fundamental vibrational modes of Trifluoperazine (TFZ) was carried out using the experimental FT-IR, FT-Raman and UV-Vis data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G (d,p) basis set. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. The HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as first hyperpolarizability of TFZ have been computed using B3LYP quantum chemical calculation.
An efficient method for calculating RMS von Mises stress in a random vibration environment
Segalman, D.J.; Fulcher, C.W.G.; Reese, G.M.; Field, R.V. Jr.
1998-02-01
An efficient method is presented for calculation of RMS von Mises stresses from stress component transfer functions and the Fourier representation of random input forces. An efficient implementation of the method calculates the RMS stresses directly from the linear stress and displacement modes. The key relation presented is one suggested in past literature, but does not appear to have been previously exploited in this manner.
Arivazhagan, M; Subhasini, V P; Austine, A
2012-02-01
The Fourier-transform infrared and FT-Raman spectra of 4-chloro-2-(trifluoromethyl) aniline (4C2TFA) were recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1) respectively. Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of 4C2TFA were carried out by density functional theory (DFT/B3LYP) method with 6-311+G(d,p) and 6-311++G(d,p) basis sets. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The values of the total dipole moment (μ) and the first order hyperpolarizability (β) of the investigated compound were computed using B3LYP/6-311++G(d,p) calculations. The calculated results also show that 4C2TFA might have microscopic non-linear optical (NLO) behavior with non-zero values. A detailed interpretation of infrared and Raman spectra of 4C2TFA is also reported. The calculated HOMO-LUMO energy gap shows that charge transfer occurs within the molecule. PMID:22074887
Strength, hardness, and lattice vibrations of Z-carbon and W-carbon: First-principles calculations
NASA Astrophysics Data System (ADS)
Li, Zhiping; Gao, Faming; Xu, Ziming
2012-04-01
The strength, hardness, and lattice vibrations of two superhard carbon allotropies, Z-carbon and W-carbon are investigated by first-principles calculations. Phonon dispersion calculations indicate that Z-carbon and W-carbon are dynamically stable at least up to 300 GPa. The strength calculations reveal that the failure mode in Z-carbon is dominated by the tensile type, and the [010] direction is the weakest one. In W-carbon, the failure mode is dominated by the shear type, and the (101)[111¯] direction is the weakest one. Although the ideal strength of diamond is distinctly greater than that of Z-carbon and W-carbon, the tensile strength and shear strength for Z-carbon and W-carbon show much lower anisotropies than that of diamond. The hardness calculations indicate that the average hardness of Z-carbon is less than that of diamond but greater than that of the W-carbon, M-carbon, and body-centered-tetragonal-C4 carbon. The simulated Raman spectra show that the Ag modes at 1094 cm-1 for Z-carbon and 1109.7 cm-1 for W-carbon are in agreement with that of 1082 cm-1 observed in the experiment of cold-compressed graphite at 9.8 GPa.
Sun, Shou -Tian; Jiang, Ling; Liu, J. W.; Heine, Nadja; Yacovitch, Tara I.; Wende, Torsten; Asmis, Knut R.; Neumark, Daniel M.; Liu, Zhi -Feng
2015-06-05
We report infrared multiple photon dissociation (IRMPD) spectra of cryogenically-cooled H_{2}PO_{4}^{-}(H_{2}O)_{n} anions (n = 2–12) in the spectral range of the stretching and bending modes of the solute anion (600–1800 cm-1). The spectra cannot be fully understood using the standard technique of comparison to harmonic spectra of minimum-energy structures; a satisfactory assignment requires considering anharmonic effects as well as entropy-driven hydrogen bond network fluctuations. Aided by finite temperature ab initio molecular dynamics simulations, the observed changes in the position, width and intensity of the IRMPD bands with cluster size are related to the sequence of microsolvation. Due to stronger hydrogen bonding to the two terminal P=O groups, these are hydrated before the two P–OH groups. By n = 6, all four end groups are involved in the hydrogen bond network and by n = 12, the cluster spectra show similarities to the condensed phase spectrum of H_{2}PO_{4}^{-}(aq). Our results reveal some of the microscopic details concerning the formation of the aqueous solvation environment around H_{2}PO_{4}^{-}, provide ample testing grounds for the design of model solvation potentials for this biologically relevant anion, and support a new paradigm for the interpretation of IRMPD spectra of microhydrated ions.
NASA Technical Reports Server (NTRS)
Lee, Timothy J.; Langhoff, Stephen R. (Technical Monitor)
1996-01-01
Due to advances in quantum mechanical methods over the last few years, it is now possible to determine ab initio potential energy surfaces in which fundamental vibrational frequencies are accurate to within +/- 8 cm(sup -1) on average, and molecular bond distances are accurate to within +/- 0.001-0.003 A, depending on the nature of the bond. That is, the potential energy surfaces have not been scaled or empirically adjusted in any way, showing that theoretical methods have progressed to the point of being useful in analyzing spectra that are not from a tightly controlled laboratory environment, such as rovibrational spectra from the interstellar medium. Some recent examples demonstrating this accuracy win be presented and discussed. These include the HNO, CH4, C2H4, and ClCN molecules. The HNO molecule is interesting due to the very large H-N anharmonicity, while ClCN has a very large Fermi resonance. The ab initio studies for the CH4 and C2H4 molecules present the first accurate full quartic force fields of any kind (i.e., whether theoretical or empirical) for a five-atom and six-atom system, respectively.
NASA Astrophysics Data System (ADS)
Tagami, Shingo; Shimizu, Yoshifumi R.
2016-02-01
Inclusion of time-odd components into the wave function is important for a reliable description of rotational motion by the angular-momentum-projection method; the cranking procedure with infinitesimal rotational frequency is an efficient way to realize it. In the present work we investigate the effect of this infinitesimal cranking for a triaxially deformed nucleus, where there are three independent cranking axes. It is found that the effects of cranking about three axes on the triaxial energy spectrum are quite different and inclusion of all of them considerably modifies the resultant spectrum from the one obtained without cranking. Employing the Gogny D1S force as an effective interaction, we apply the method to the calculation of the multiple γ vibrational bands in 164Er as a typical example, where the angular-momentum-projected configuration mixing with respect to the triaxial shape degree of freedom is performed. With this method, both the K =0 and the K =4 two-phonon γ vibrational bands are obtained with considerable anharmonicity. Reasonably good agreement, though not perfect, is obtained for both the spectrum and transition probabilities with rather small average triaxial deformation γ ≈9∘ for the ground-state rotational band. The relation to the wobbling motion at high-spin states is also briefly discussed.
NASA Astrophysics Data System (ADS)
Poulin, Nicolas M.; Bramley, Matthew J.; Carrington, Tucker, Jr.; Kjaergaard, Henrik G.; Henry, Bryan R.
1996-05-01
We use the recursive residue generation method (RRGM) with an exact kinetic energy operator to calculate vibrational excitation energies and band intensities for formaldehyde. The basis is a product of one-dimensional potential optimized discrete variable representation (PO-DVR) functions for each coordinate. We exploit the symmetry by using symmetry adapted basis functions obtained by taking linear combinations of PO-DVR functions. Our largest basis set consists of 798 600 functions (per symmetry block). The Lanczos tridiagonal representation of the Hamiltonian is generated iteratively (without constructing matrix elements explicitly) by sequential transformations. We determine a six-dimensional dipole moment function from the ab initio dipole moment values computed at the QCISD level with a 6-311++G(d,p) basis set. We converged all A1, B2 and B1 vibrational states up to the combination band with two quanta in the C-O stretch and one quantum in a C-H stretch at about 6 350 cm-1 above zero point energy. We present a simulated (J=0) infrared spectrum of CH2O for transitions from the ground state.
Higher harmonic control for rotary wing aircraft
NASA Technical Reports Server (NTRS)
Gupta, B. P.; Logan, A. H.; Wood, E. R.
1984-01-01
Higher Harmonic Control reduces helicopter airframe vibration through the exercise of rotor blade pitch control at frequencies that are higher harmonics of rotor rotation. Analysis wind tunnel tests and flight tests of this technology with an OH-6A helicopter have led to vibration reduction levels of the order of more than 80 percent. Blade feathering capability at rotor speed harmonics other than the first also promises the improvement of such rotor characteristics as acoustics, aerodynamic efficiency and ground resonance.
Vibrational spectroscopic study and structure calculation for model compounds and polyurethanes
Wang, Q.
1992-01-01
Vibrational spectroscopy has been applied to the study of a small ring molecule, three model urethane compounds and Poly[4,4[prime]-bis(6-hydroxyhexyloxy)biphenyl-co-2,4-toluenediisocyanate] (2,4-TDI polyurethane) systems. The computer program POLYGRAF was used to estimate the stability of some conformers of the three model compounds. Grazing angle microscopy was used to study the surface structure of thin films of polyurethane. The synthesis, far infrared spectra, temperature dependent mid-infrared spectra and the Fourier transform Raman spectra are reported for polycrystalline samples of three model urethanes, 1,3-phenyl di(methyl carbamate) (1,3-PDI based urethane), 2,6-toluene di(methyl carbamate) (2,6-TDI based urethane), and 2,4-toluene di(methyl carbamate) (2,4-TDI based urethane). Geometry optimization is reported for phenyl methyl carbamate by ab initio and molecular mechanics methods, and of the three model urethanes by molecular mechanics methods using the Dreiding I force field. The results suggest that in isotropic surroundings only a very small number of the many possible conformers of the urethane groups in these molecules contribute appreciably to the structure. The intermolecular interaction, morphology and microstructure of 2,4-TDI polyurethane are studied. A molecular interpretation of hydrogen bonding behavior is given. The temperature dependence of infrared spectra of the 2,4-TDI polyurethane films are reported together with some kinetic data. A very thin film was prepared to study the surface behavior of 2,4-TDI polyurethane. An infrared spectrum was obtained by grazing angle reflection-absorption. The results suggest that 2,4-TDI polyurethane has a layered structure and that most of the NH groups and carbonyl groups are free on the surface. The infrared spectra of 1,4-cyclohexadiene and 1,4-cyclohexadiene-3,3,6,6-d4 were recorded in the gas phase at room temperature.
NASA Astrophysics Data System (ADS)
Ben hassen, C.; Boujelbene, M.; Bahri, M.; Zouari, N.; Mhiri, T.
2014-09-01
The present paper undertakes the study of a new hybrid compound [2-CH3C6H4NH3]2SeO4 characterized by the X-ray diffraction, IR, DFT calculation, TG-DTA, DSC and electrical conductivity. This new organic-inorganic hybrid compound crystallizes in the monoclinic system with P21/c space group and the following parameters a = 14.821 (5) Å; b = 16.245 (5) Å; c = 6.713 (5) Å; ß = 102.844 (5)°, Z = 4 and V = 1575.8 (14) Å3. The atomic arrangement can be described as isolated tetrahedral SeO42- connected with the organic groups by means of Nsbnd H⋯O hydrogen bonds to form infinite sinusoidal chains in the c-direction. BHHLYP/6-311g** method was used to determine the harmonic frequencies for two optimized cluster structures. The calculated modes were animated using the Molden graphical package to give tentative assignments of the observed IR spectra. Thermal analysis of the title compound does not indicate the occurrence of a phase transition in the temperature range of 300-650 K. Dielectric study of this compound has been measured, in order to determine the conductivity. The conductivity relaxation parameters associated with some H+ conduction have been determined from an analysis of the M″/M″max spectrum measured in a wide temperature range.
Identification of hydrogen defects in SrTiO3 by first principles local vibrational mode calculations
T-Thienprasert, J; Fongkaew, Ittipon; Singh, David J; Du, Mao-Hua; Limpijumnong, Sukit
2012-01-01
For over three decades, the infrared spectroscopy peaks of around 3500 cm{sup -1} observed in hydrogen-doped SrTiO{sub 3} samples have been assigned to an interstitial hydrogen (H{sub i}) attached to a lattice oxygen with two possible configuration models: the octahedral edge (OE) and the cubic face (CF) models. Based on our first-principles calculations of H{sub i} around O, both OE and CF configurations are not energetically stable. Starting from either configuration, the H{sub i} would spontaneously relax into an off axis (OA) site; lowering the energy by 0.25 eV or more. The calculated vibrational frequency of 2745 cm{sup -1} for OA invalidates the assignment of H{sub i} to the observed 3500 cm{sup -1} peak. In addition, the calculated diffusion barrier is low, suggesting that H{sub i} can be easily annealed out. We propose that the observed peaks around 3500 cm{sup -1} are associated with defect complexes. A Sr vacancy (V{sub Sr}) can trap H{sub i} and form a H-V{sub Sr} complex which is both stable and has the frequency in agreement with the observed main peak. The complex can also trap another H{sub i} and form 2H-V{sub Sr}; consistent with the observed additional peaks at slightly higher frequencies (3510-3530 cm{sup -1}).
Chowdhry, Babur Z; Ryall, John P; Dines, Trevor J; Mendham, Andrew P
2015-11-19
IR and Raman spectra of eugenol, isoeugenol and methyl eugenol have been obtained in the liquid phase. Vibrational spectroscopic results are discussed in relation to computed structures and spectra of the low energy conformations of these molecules obtained from DFT calculations at the B3LYP/cc-pVTZ level. Although computed differences in vibrational spectra for the different conformers were generally small, close examination, in conjunction with the experimental spectra, enabled conformational analysis of all three molecules. Anharmonic contributions to computed vibrational spectra were obtained from calculations of cubic and quartic force constants at the B3LYP/DZ level. This permitted the determination of the anharmonic fundamentals for comparison with the experimental IR and Raman band positions, leading to an excellent fit between calculated and experimental spectra. Band assignments were obtained in terms of potential energy distributions (ped's). PMID:26496173
NASA Astrophysics Data System (ADS)
Mark, William D.
2015-10-01
The transmission-error frequency spectrum of meshing gear pairs, operating at constant speed and constant loading, is decomposed into harmonics arising from the fundamental period of the gear pair, rotational harmonics of the individual gears of the pair, and tooth-meshing harmonics. In the case of hunting-tooth gear pairs, no rotational harmonics from the individual gears, other than the tooth-meshing harmonics, are shown to occur at the same frequencies. Time-synchronous averages utilizing a number of contiguous revolutions of the gear of interest equal to an integer multiple of the number of teeth on the mating gear is shown to eliminate non-tooth-meshing transmission-error rotational-harmonic contributions from the mating gear, and those from the gear pair, in the case of hunting-tooth gear pairs, and to minimize these contributions in the case of non-hunting-tooth gear pairs. An example computation is shown to illustrate the effectiveness of the suggested time-synchronous-averaging procedure.
Calculation of Dynamic Loads Due to Random Vibration Environments in Rocket Engine Systems
NASA Technical Reports Server (NTRS)
Christensen, Eric R.; Brown, Andrew M.; Frady, Greg P.
2007-01-01
An important part of rocket engine design is the calculation of random dynamic loads resulting from internal engine "self-induced" sources. These loads are random in nature and can greatly influence the weight of many engine components. Several methodologies for calculating random loads are discussed and then compared to test results using a dynamic testbed consisting of a 60K thrust engine. The engine was tested in a free-free condition with known random force inputs from shakers attached to three locations near the main noise sources on the engine. Accelerations and strains were measured at several critical locations on the engines and then compared to the analytical results using two different random response methodologies.
NASA Astrophysics Data System (ADS)
Mezei, J. Zs; Backodissa-Kiminou, R. D.; Tudorache, D. E.; Morel, V.; Chakrabarti, K.; Motapon, O.; Dulieu, O.; Robert, J.; Tchang-Brillet, W.-Ü. L.; Bultel, A.; Urbain, X.; Tennyson, J.; Hassouni, K.; Schneider, I. F.
2015-06-01
The latest molecular data—potential energy curves and Rydberg/valence interactions—characterizing the super-excited electronic states of CO are reviewed, in order to provide inputs for the study of their fragmentation dynamics. Starting from this input, the main paths and mechanisms for CO+ dissociative recombination are analyzed; its cross sections are computed using a method based on multichannel quantum defect theory. Convoluted cross sections, giving both isotropic and anisotropic Maxwellian rate coefficients, are compared with merged-beam and storage-ring experimental results. The calculated cross sections underestimate the measured ones by a factor of two, but display a very similar resonant shape. These facts confirm the quality of our approach for the dynamics, and call for more accurate and more extensive molecular structure calculations.
Theoretical calculations and vibrational potential energy surface of 4-silaspiro(3,3)heptane
Ocola, Esther J.; Medders, Cross; Laane, Jaan; Meinander, Niklas
2014-04-28
Theoretical computations have been carried out on 4-silaspiro(3,3)heptane (SSH) in order to calculate its molecular structure and conformational energies. The molecule has two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. Energy calculations were carried out for different conformations of SSH. These results allowed the generation of a two-dimensional ring-puckering potential energy surface (PES) of the form V = a(x{sub 1}{sup 4} + x{sub 2}{sup 4}) – b(x{sub 1}{sup 2} + x{sub 2}{sup 2}) + cx{sub 1}{sup 2}x{sub 2}{sup 2}, where x{sub 1} and x{sub 2} are the ring-puckering coordinates for the two rings. The presence of sufficiently high potential energy barriers prevents the molecule from undergoing pseudorotation. The quantum states, wave functions, and predicted spectra resulting from the PESs were calculated.
Vibrational spectroscopic study of fluticasone propionate.
Ali, H R H; Edwards, H G M; Kendrick, J; Scowen, I J
2009-03-01
Fluticasone propionate is a synthetic glucocorticoid with potent anti-inflammatory activity that has been used effectively in the treatment of chronic asthma. The present work reports a vibrational spectroscopic study of fluticasone propionate and gives proposed molecular assignments on the basis of ab initio calculations using BLYP density functional theory with a 6-31G* basis set and vibrational frequencies predicted within the quasi-harmonic approximation. Several spectral features and band intensities are explained. This study generated a library of information that can be employed to aid the process monitoring of fluticasone propionate. PMID:19095495
Vibrational spectroscopic study of terbutaline hemisulphate.
Ali, H R H; Edwards, H G M; Kendrick, J; Scowen, I J
2009-05-01
The Raman spectrum of terbutaline hemisulphate is reported for the first time, and molecular assignments are proposed on the basis of ab initio BLYP DFT calculations with a 6-31G* basis set and vibrational frequencies predicted within the quasi-harmonic approximation; these predictions compare favourably with the observed vibrational spectra. Comparison with previously published infrared data explains several spectral features. The results from this study provide data that can be used for the preparative process monitoring of terbutaline hemisulphate, an important beta(2) agonist drug in various dosage forms and its interaction with excipients and other components. PMID:19124270
Lee, Christopher M; Mohamed, Naseer M A; Watts, Heath D; Kubicki, James D; Kim, Seong H
2013-06-01
Sum-frequency-generation (SFG) vibration spectroscopy selectively detects noncentrosymmetric vibrational modes in crystalline cellulose inside intact lignocellulose. However, SFG peak assignment in biomass samples is challenging due to the complexity of the SFG processes and the lack of reference SFG spectra from the two crystal forms synthesized in nature, cellulose I? and I?. This paper compares SFG spectra of laterally aligned cellulose I? and I? crystals with vibration frequencies calculated from density functional theory with dispersion corrections (DFT-D2). Two possible hydrogen-bond networks A and B ( Nishiyama et al. Biomacromolecules 2008 , 9 , 3133 ) were investigated for both polymorphs. From DFT-D2 calculations the energetically favorable structures for cellulose I? and I? had CH2OH groups in tg conformations and network A hydrogen bonding. The calculated frequencies of C-H stretch modes agreed reasonably well with the peak positions observed with SFG and were localized vibrations; thus, peak assignments to specific alkyl groups were proposed. DFT-D2 calculations underestimated the distances between hydrogen-bonded oxygen atoms compared to the experimentally determined values; therefore, the OH stretching calculated frequencies were ~100 cm(-1) lower than observed. The SFG peak assignments through comparison with DFT-D2 calculations will guide the SFG analysis of the crystalline cellulose structure in plant cell walls and lignocellulose biomass. PMID:23738844
Miliordos, Evangelos; Apra, Edoardo; Xantheas, Sotiris S.
2013-09-21
We report the first optimum geometries and harmonic vibrational frequencies for the ring pentamer and several water hexamer (prism, cage, cyclic and two book) at the CCSD(T)/aug-cc-pVDZ level of theory. All five hexamer isomer minima previously reported by MP2 are also minima on the CCSD(T) potential energy surface (PES). In addition, all CCSD(T) minimum energy structures for the n=2-6 cluster isomers are quite close to the ones previously obtained by MP2 on the respective PESs, as confirmed by a modified Procrustes analysis that quantifies the difference between any two cluster geometries. The CCSD(T) results confirm the cooperative effect of the homodromic ring networks (systematic contraction of the nearest-neighbor (nn) intermolecular separations with cluster size) previously reported by MP2, albeit with O-O distances shorter by ~0.02 , indicating that MP2 overcorrects this effect. The harmonic frequencies at the minimum geometries were obtained by the double differentiation of the CCSD(T) energy using an efficient scheme based on internal coordinates that reduces the number of required single point energy evaluations by ~15% when compared to the corresponding double differentiation using Cartesian coordinates. Negligible differences between MP2 and CCSD(T) are found for the librational modes, while uniform increases of ~15 and ~25 cm-1 are observed for the bending and free OH harmonic frequencies. The largest differences between MP2 and CCSD(T) are observed for the harmonic hydrogen bonded frequencies. The CCSD(T) red shifts from the monomer frequencies (??) are smaller than the MP2 ones, due to the fact that the former produces shorter elongations (?R) of the respective hydrogen bonded OH lengths from the monomer value with respect to the latter. Both the MP2 and CCSD(T) results for the hydrogen bonded frequencies were found to closely follow the relation - ?? = s ? ?R, with a rate of s = 20.3 cm-1 / 0.001 . The CCSD(T) harmonic frequencies, when corrected using the MP2 anharmonicities obtained from second order vibrational perturbation theory (VPT2), produce anharmonicCCSD(T) estimates that are within < 60 cm-1 from the measured infrared (IR) active bands of the n=2-6 clusters and furthermore trace the observed red shifts with respect to the monomer (??) quite accurately. The energetic order between the various hexamer isomers on the PES (prism has the lowest energy) previously reported at MP2 was found to be preserved at the CCSD(T) level, whereas the inclusion of anharmonic corrections further stabilizes the cage among the hexamer isomers.
NASA Astrophysics Data System (ADS)
Wang, Yimin; Carter, Stuart; Braams, Bastiaan J.; Bowman, Joel M.
2008-02-01
We report vibrational configuration interaction calculations of the monomer fundamentals of (H2O)2, (D2O)2, (H2O)3, and (D2O)3 using the code MULTIMODE and full dimensional ab initio-based global potential energies surfaces (PESs). For the dimer the HBB PES [Huang et al., J. Chem. Phys 128, 034312 (2008)] is used and for the trimer a new PES, reported here, is used. The salient properties of the new trimer PES are presented and compared to previous single-point calculations and the vibrational energies are compared with experiments.
NASA Astrophysics Data System (ADS)
Searle, G. F. C.
2014-05-01
1. Elementary theory of harmonic motion; 2. Experimental work in harmonic motion; Experiment 1. Determination of g by a simple pendulum; Experiment 2. Harmonic motion of a body suspended by a spring; Experiment 3. Harmonic motion of a rigid body suspended by a torsion wire; Experiment 4. Study of a system with variable moment of inertia; Experiment 5. Dynamical determination of ratio of couple to twist for a torsion wire; Experiment 6. Comparison of the moments of inertia of two bodies; Experiment 7. Experiment with a pair of inertia bars; Experiment 8. Determination of the moment of inertia of a rigid pendulum; Experiment 9. Experiment on a pendulum with variable moment of inertia; Experiment 10. Determination of g by a rigid pendulum; Experiment 11. Pendulum on a yielding support; Experiment 12. Determination of the radius of curvature of a concave mirror by the oscillations of a sphere rolling in it; Experiment 13. Determination of g by the oscillations of a rod rolling on a cylinder; Experiment 14. Study of a vibrating system with two degrees of freedom; Note 1. On the vibration of a body suspended from a light spring; Note 2. Periodic time of a pendulum vibrating through a finite arc; Note 3. Periodic time for finite motion; Note 4. Periodic times of a pendulum with two degrees of freedom.
NASA Astrophysics Data System (ADS)
Joshi, Bhawani Datt; Srivastava, Anubha; Honorato, Sara Braga; Tandon, Poonam; Pessoa, Otília Deusdênia Loiola; Fechine, Pierre Basílio Almeida; Ayala, Alejandro Pedro
2013-09-01
Oncocalyxone A (C17H18O5) is the major secondary metabolite isolated from ethanol extract from the heartwood of Auxemma oncocalyx Taub popularly known as “pau branco”. Oncocalyxone A (Onco A) has many pharmaceutical uses such as: antitumor, analgesic, antioxidant and causative of inhibition of platelet activation. We have performed the optimized geometry, total energy, conformational study, molecular electrostatic potential mapping, frontier orbital energy gap and vibrational frequencies of Onco A employing ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method with 6-311++G(d, p) basis set. Stability of the molecule arising from hyperconjugative interactions and/or charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV-vis spectrum of the compound was recorded in DMSO and MeOH solvent. The TD-DFT calculations have been performed to explore the influence of electronic absorption spectra in the gas phase, as well as in solution environment using IEF-PCM and 6-31G basis set. The 13C NMR chemical shifts have been calculated with the B3LYP/6-311++G(d, p) basis set and compared with the experimental values. These methods have been used as tools for structural characterization of Onco A.
NASA Astrophysics Data System (ADS)
Leclerc, Arnaud; Carrington, Tucker
2014-05-01
We propose an iterative method for computing vibrational spectra that significantly reduces the memory cost of calculations. It uses a direct product primitive basis, but does not require storing vectors with as many components as there are product basis functions. Wavefunctions are represented in a basis each of whose functions is a sum of products (SOP) and the factorizable structure of the Hamiltonian is exploited. If the factors of the SOP basis functions are properly chosen, wavefunctions are linear combinations of a small number of SOP basis functions. The SOP basis functions are generated using a shifted block power method. The factors are refined with a rank reduction algorithm to cap the number of terms in a SOP basis function. The ideas are tested on a 20-D model Hamiltonian and a realistic CH3CN (12 dimensional) potential. For the 20-D problem, to use a standard direct product iterative approach one would need to store vectors with about 1020 components and would hence require about 8 × 1011 GB. With the approach of this paper only 1 GB of memory is necessary. Results for CH3CN agree well with those of a previous calculation on the same potential.
Joshi, Bhawani Datt; Srivastava, Anubha; Honorato, Sara Braga; Tandon, Poonam; Pessoa, Otília Deusdênia Loiola; Fechine, Pierre Basílio Almeida; Ayala, Alejandro Pedro
2013-09-01
Oncocalyxone A (C17H18O5) is the major secondary metabolite isolated from ethanol extract from the heartwood of Auxemma oncocalyx Taub popularly known as "pau branco". Oncocalyxone A (Onco A) has many pharmaceutical uses such as: antitumor, analgesic, antioxidant and causative of inhibition of platelet activation. We have performed the optimized geometry, total energy, conformational study, molecular electrostatic potential mapping, frontier orbital energy gap and vibrational frequencies of Onco A employing ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method with 6-311++G(d,p) basis set. Stability of the molecule arising from hyperconjugative interactions and/or charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV-vis spectrum of the compound was recorded in DMSO and MeOH solvent. The TD-DFT calculations have been performed to explore the influence of electronic absorption spectra in the gas phase, as well as in solution environment using IEF-PCM and 6-31G basis set. The (13)C NMR chemical shifts have been calculated with the B3LYP/6-311++G(d,p) basis set and compared with the experimental values. These methods have been used as tools for structural characterization of Onco A. PMID:23747376
NASA Astrophysics Data System (ADS)
Smirnov, Alex I.
2008-01-01
This communication reports on post-processing of continuous wave EPR spectra by a digital convolution with filter functions that are subjected to differentiation or the Kramers-Krnig transform analytically. In case of differentiation, such a procedure improves spectral resolution in the higher harmonics enhancing the relative amplitude of sharp spectral features over the broad lines. At the same time high-frequency noise is suppressed through filtering. These features are illustrated on an example of a Lorentzian filter function that has a principal advantage of adding a known magnitude of homogeneous broadening to the spectral shapes. Such spectral distortion could be easily and accurately accounted for in the consequent least-squares data modeling. Application examples include calculation of higher harmonics from pure absorption echo-detected EPR spectra and resolving small hyperfine coupling that are unnoticeable in conventional first derivative EPR spectra. Another example involves speedy and automatic separation of fast and broad slow-motion components from spin-label EPR spectra without explicit simulation of the slow motion spectrum. The method is illustrated on examples of X-band EPR spectra of partially aggregated membrane peptides.
NASA Astrophysics Data System (ADS)
Atalay, Y.; Ucun, F.; Avc?, D.; Ba?o?lu, A.
2006-06-01
The vibrational frequencies and molecular geometry of (R)- and (rac)-4-phenly-1,3-oxazolidin-2-one (4-POO) in the ground state have been calculated using the Hartree-Fock and density functional method (B3LYP) with 6-31G(d) basis set. The optimized geometric bond lengths are described better by HF while bond angles are reproduced more accurately by DFT (B3LYP). Comparison of the observed fundamental vibrational frequencies of (R)-POO and (rac)-4-POO and calculated results by density functional B3LYP and Hartree-Fock methods indicate that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems.
NASA Astrophysics Data System (ADS)
Clemy Monicka, J.; James, C.
2015-09-01
FTIR and Raman spectral techniques were employed for the vibrational characterization of the herbicide mefenacet. The equilibrium geometry, various bonding features and harmonic vibrational wavenumbers were investigated with the help of density functional theory calculations. A detailed assignment of the vibrational spectra was made with the aid of theoretically predicted vibrational frequencies. Natural bond orbital analysis on mefenacet was carried out to reveal the nature of different interactions responsible for electron delocalization and the charge transfer between the orbitals (n ? ??, n ? ??, ? ? ??). Structural changes in the molecule due to the substitution of highly electronegative oxygen atom, conjugation and resonance effect were analyzed.
Anharmonic contributions to the inversion vibration in 2-aminopyrimidine
McCarthy, W.J.; Lapinski, L.; Nowak, M.J.
1995-07-08
The out-of-plane vibrations of the amino group in 2-aminopyrimidine have large amplitudes, and cannot be properly described within the harmonic approximation. The normal mode analysis carried out at this level of approximation at the restricted Hartree--Fock level and at the second-order Moller--Plesset perturbation theory level failed to match the experimental transition frequency of {nu}{approx}200 cm{sup {minus}1} of the inversion vibration in this compound. In an effort to better understand this vibration motion, we went beyond the harmonic approximation. The inversion vibration was treated as being uncoupled from all other nuclear degrees of freedom. An internal coordinate ({omega}) was chosen whose displacement mimicked the out-of-plane distortion of the amino group during the inversion vibration. Electronic energy was calculated at the second-order Moller--Plesset perturbation theory level at selected values of {omega} to form a double-well curve describing a model potential within which the nuclei move during the vibration. This potential was incorporated into a one-dimensional Hamiltonian, and vibrational energy expectation values were variationally determined by utilizing the harmonic wavefunctions as the basis set. Two sets of calculations were performed: one in which the mirror plane of symmetry was preserved throughout the vibrational deformation limiting the internal coordinates to 17, and another in which the symmetry was unconstrained permitting description by 3{ital N}{minus}6=30 internal coordinates. These calculations resulted in prediction of the {ital v}=0{r_arrow}{ital v}=1 transition energy of {nu}=130.1 cm{sup {minus}1} and {nu}=206.7 cm{sup {minus}1}, respectively, reasonably matching the experimental value of {approx}200 cm{sup {minus}1}. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Anharmonic contributions to the inversion vibration in 2-aminopyrimidine
NASA Astrophysics Data System (ADS)
McCarthy, W. J.; Lapinski, L.; Nowak, M. J.; Adamowicz, L.
1995-07-01
The out-of-plane vibrations of the amino group in 2-aminopyrimidine have large amplitudes, and cannot be properly described within the harmonic approximation. The normal mode analysis carried out at this level of approximation at the restricted Hartree-Fock level and at the second-order Mller-Plesset perturbation theory level failed to match the experimental transition frequency of ??200 cm-1 of the inversion vibration in this compound. In an effort to better understand this vibration motion, we went beyond the harmonic approximation. The inversion vibration was treated as being uncoupled from all other nuclear degrees of freedom. An internal coordinate (?) was chosen whose displacement mimicked the out-of-plane distortion of the amino group during the inversion vibration. Electronic energy was calculated at the second-order Mller-Plesset perturbation theory level at selected values of ? to form a double-well curve describing a model potential within which the nuclei move during the vibration. This potential was incorporated into a one-dimensional Hamiltonian, and vibrational energy expectation values were variationally determined by utilizing the harmonic wavefunctions as the basis set. Two sets of calculations were performed: one in which the mirror plane of symmetry was preserved throughout the vibrational deformation limiting the internal coordinates to 17, and another in which the symmetry was unconstrained permitting description by 3N-6=30 internal coordinates. These calculations resulted in prediction of the v=0?v=1 transition energy of ?=130.1 cm-1 and ?=206.7 cm-1, respectively, reasonably matching the experimental value of ?200 cm-1.
DVR3D: a program suite for the calculation of rotation-vibration spectra of triatomic molecules
NASA Astrophysics Data System (ADS)
Tennyson, Jonathan; Kostin, Maxim A.; Barletta, Paolo; Harris, Gregory J.; Polyansky, Oleg L.; Ramanlal, Jayesh; Zobov, Nikolai F.
2004-11-01
The DVR3D program suite calculates energy levels, wavefunctions, and where appropriate dipole transition moments, for rotating and vibrating triatomic molecules. Potential energy and, where necessary, dipole surfaces must be provided. Expectation values of geometrically defined functions can be calculated, a feature which is particularly useful for fitting potential energy surfaces. The programs use an exact (within the Born-Oppenheimer approximation) Hamiltonian and offer a choice of Jacobi or Radau internal coordinates and several body-fixed axes. Rotationally excited states are treated using an efficient two-step algorithm. The programs uses a Discrete Variable Representation (DVR) based on Gauss-Jacobi and Gauss-Laguerre quadrature for all 3 internal coordinates and thus yields a fully point-wise representation of the wavefunctions. The vibrational step uses successive diagonalisation and truncation which is implemented for a number of possible coordinate orderings. The rotational, expectation value and transition dipole programs exploit the savings offered by performing integrals on a DVR grid. The new version has been rewritten in FORTRAN 90 to exploit the dynamic array allocations and the algorithm for dipole and spectra calculations have been substantially improved. New modules allow the z-axis to be embedded perpendicular to the plane of the molecule and for the calculation of expectation values. Program summaryTitle of the program: DVR3D suite Catalogue number: ADTI Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADTI Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Programming language: Fortran 90 No. of lines in distributed program, including test data, etc.: 61 574 No. of bytes in distributed program, including test data, etc.: 972 404 Distribution format: tar.gz New version summaryTitle of program: DVR3DRJZ Catalogue number: ADTB Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADTB Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Reference in CPC to previous version: 86 (1995) 175 Catalogue identifier of previous version: ADAK Authors of previous version: J. Tennyson, J.R. Henderson and N.G. Fulton Does the new version supersede the original program?: DVR3DRJZ supersedes DVR3DRJ Computer: PC running Linux Installation: desktop Other machines on which program tested: Compaq running True64 Unix; SGI Origin 2000, Sunfire V750 and V880 systems running SunOS, IBM p690 Regatta running AIX Programming language used in the new version: Fortran 90 Memory required to execute: case dependent No. of lines in distributed program, including test data, etc.: 4203 No. of bytes in distributed program, including test data, etc.: 30 087 Has code been vectorised or parallelised?: The code has been extensively vectorised. A parallel version of the code, PDVR3D has been developed [1], contact the first author for details Additional keywords: perpendicular embedding Distribution format: gz Nature of physical problem: DVR3DRJZ calculates the bound vibrational or Coriolis decoupled rotational-vibrational states of a triatomic system in body-fixed Jacobi (scattering) or Radau coordinates [2] Method of solution: All coordinates are treated in a discrete variable representation (DVR). The angular coordinate uses a DVR based on (associated) Legendre polynomials and the radial coordinates utilise a DVR based on either Morse oscillator-like or spherical oscillator functions. Intermediate diagonalisation and truncation is performed on the hierarchical expression of the Hamiltonian operator to yield the final secular problem. DVR3DRJ provides the vibrational wavefunctions necessary for ROTLEV3, ROLEV3B or ROTLEV3Z to calculate rotationally excited states, DIPOLE3 to calculate rotational-vibrational transition strengths and XPECT3 to compute expectation values Restrictions on the complexity of the problem: (1) The size of the final Hamiltonian matrix that can practically be diagonalised. (2) The order of integration in the radial coordinates that can be dealt with within the machine exponent range. Some adjustment in the code may be necessary when large order Gauss-Laguerre quadrature is used Typical running time: Case dependent but usually dominated by the final (3D) matrix diagonalisation. The test runs take minutes on a fast PC Unusual features of the program: A user supplied subroutine containing the potential energy as an analytic function is a program requirement References:H.Y. Mussa, J. Tennyson, Comput. Phys. Commun. 128 (2000) 434. J. Tennyson, B.T. Sutcliffe, Internat. J. Quantum Chem. 42 (1992) 941. New version summaryTitle of program: ROTLEV3 Catalogue number: ADTC Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADTC Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Reference in CPC to previous version: 86 (1995) 175 Catalogue identifier of previous version: ADAL Authors of previous version: J. Tennyson, J.R. Henderson and N.G. Fulton Does the new version supersede the original program?: Yes Computer: PC running Linux Installation: desktop Other machines on which program tested: Compaq running True64 Unix; SGI Origin 2000, Sunfire V750 and V880 systems running SunOS Programming language used: Fortran 90 High speed storage required: case dependent No. of lines in distributed program, including test data, etc.: 1514 No. of bytes in distributed program, including test data, etc.: 12 652 Has code been vectorised or parallelised?: The code has been extensively vectorised. A parallel version of the code, PROTLEV3 has been developed [1], contact the first author for details Distribution format: gz Nature of physical problem: ROTLEV3 performs the second step in a two-step variational calculation for the bound rotational-vibrational levels of a triatomic system represented in either Jacobi or unsymmetrised Radau coordinates Method of solution: A basis is constructed from the solutions of the Coriolis decoupled problem provided by DVR3DRJZ. The angular coordinate is transformed back to a basis set representation. The sparse Hamiltonian matrix can be diagonalised iteratively or in core Restrictions on the complexity of the problem: The size of matrix that can practically be diagonalised Typical running time: Case dependent. The sample data takes less than a minute on a fast PC Unusual features of the program: Most data is read directly from DVR3DRJZ. ROTLEV3 can provide data to drive DIPOLE3 and/or XPECT3 References: [1] H.Y. Mussa, J. Tennyson, Comput. Phys. Commun. 128 (2000) 434. New version summaryTitle of program: ROTLEV3B Catalogue number: ADTD Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADTD Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Reference in CPC to previous version: 86 (1995) 175 Catalogue identifier of previous version: ADAM Authors of previous version: J. Tennyson, J.R. Henderson and N.G. Fulton Does the new version supersede the original program?: Yes Computer: PC running Linux Installation: desktop Other machines on which program tested: Compaq running True64 Unix, Sunfire V750 and V880 systems running SunOS Programming language used: Fortran 90 High speed storage required: case dependent No. of lines in distributed program, including test data, etc.: 2215 No. of bytes in distributed program, including test data, etc.: 16 595 Has code been vectorised or parallelised?: The code has been extensively vectorised. A parallel version of the code, PROTLEV3B has been developed [1], contact the first author for details Distribution format: gz Nature of physical problem: ROTLEV3B performs the second step in a two-step variational calculation for the bound rotational-vibrational levels of a triatomic system represented by symmetrised Radau coordinates using a bisector embedding [2] Method of solution: A basis is constructed from the solutions of the Coriolis decoupled problem provided by DVR3DRJZ. The problem is constructed entirely within the DVR. The Hamiltonian matrix can be diagonalised iteratively or in core Restrictions on the complexity of the problem: The size of matrix that can practically be diagonalised Typical running time: Case dependent. The sample data takes a few minutes on a fast PC Unusual features of the program: Most data is read directly from DVR3DRJZ. ROTLEV3B can provide data to drive DIPOLE3 and/or XPECT3 References:H.Y. Mussa, J. Tennyson, Comput. Phys. Commun. 128 (2000) 434. J. Tennyson, B.T. Sutcliffe, Internat. J. Quantum Chem. 42 (1992) 941. Program summaryTitle of program: ROTLEV3Z Catalogue number: ADTE Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADTE Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer: PC running Linux Installation: desktop Other machines on which program tested: Compaq running True64 Unix, Sunfire V750 and V880 systems running SunOS Programming language used: Fortran 90 High speed storage required: case dependent No. of lines in distributed program, including test data, etc.: 2919 No. of bytes in distributed program, including test data, etc.: 17 241 Keywords: rotationally excited state, Coriolis coupling, secondary variational method, sparse matrix, vectorised, perpendicular embedding, Radau coordinates Has code been vectorised or parallelised?: The code has been extensively vectorised Distribution format: gz Nature of physical problem: ROTLEV3Z performs the second step in a two-step variational calculation for the bound rotational-vibrational levels of a triatomic system represented by symmetrised Radau coordinates using a perpendicular embedding [1] Method of solution: A basis is constructed from the solutions of the Coriolis decoupled problem provided by DVR3DRJZ. The problem is constructed entirely within the DVR. The Hamiltonian matrix is diagonalised in core Restrictions on the complexity of the problem: The size of matrix that can practically be diagonalised Typical running time: Case dependent. The sample data takes a few minutes on a fast PC Unusual features of the program: Most data is read directly from DVR3DRJZ References: [1] M.A. Kostin, O.L. Polyansky, J.Tennyson, J. Chem. Phys. 116 (2002) 7564. New version summaryTitle of program: DIPOLE3 Catalogue number: ADTF Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADTF Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Reference in CPC to previous version: 86 (1995) 175 Catalogue identifier of previous version: ADAN Authors of previous version: J. Tennyson, J.R. Henderson and N.G. Fulton Does the new version supersede the original program?: Yes Computer: PC running Linux Installation: desktop Other machines on which program tested: Compaq running True64 Unix; SGI Origin 2000; sunfire V750 and V880 systems Programming language used: Fortran 90 High speed storage required: case dependent No. of lines in distributed program, including test data, etc.: 1921 No. of bytes in distributed program, including test data, etc.: 15 685 Has code been vectorised or parallelised?: The code has been extensively vectorised. Commands to parallelise the code using OpenMP are included in the source Distribution format: gz Nature of physical problem: DIPOLE3 calculates dipole transition intensities between previously calculated wavefunction for both rotational and rotational-vibrational transitions Method of solution: Integrals over dipole surfaces are constructed using a DVR in all three coordinates, this requires a transformation of the angular wavefunctions. Wavefunctions generated by DVR3DRJZ and ROTLEV3 or ROTLEV3B are then used to give transition intensities for individual pairs of states Restrictions on the complexity of the problem: The complexity of the problem that can be solved by DVR3DRJZ, ROTLEV3 or ROTLEV3B Typical running time: Case dependent. The test data takes a few seconds on a fast PC Unusual features of the program: Most data is read directly from DVR3DRJZ and ROTLEV3 or ROTLEV3B. DIPOLE provides data to drive SPECTRA New version summaryTitle of program: SPECTRA Catalogue number: ADTG Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADTG Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer: PC running Linux Installation: desktop Other machines on which program tested: Compaq running True64 Unix Reference in CPC to previous version: 75 (1993) 339 Catalogue identifier of previous version: ACNB Authors of previous version: J. Tennyson, S. Miller and C.R. Le Sueur Does the new version supersede the original program?: Yes Programming language used: Fortran 90 High speed storage required: case dependent No. of lines in distributed program, including test data, etc.: 1037 No. of bytes in distributed program, including test data, etc.: 9159 Has code been vectorised or parallelised?: As execution times are very short this is usually not important Distribution format: gz Nature of physical problem: SPECTRA generates synthetic, frequency ordered spectra as a function of temperature. Absolute intensities can be calculated if the necessary data to calculate the partition function is supplied Method of solution: Transitions are sorted by frequency and weighted using Boltzmann statistics Restrictions on the complexity of the problem: The complexity of problem that can be solved by other programs in the suite Typical running time: Case dependent, but very small for sample data Unusual features of the program: Most data is read directly from DIPOLE3. Some data from DVR3DRJZ and ROTLEV3 or ROTLEV3B may also be required Program summaryTitle of program: XPECT3 Catalogue number: ADTH Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADTH Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer: PC running Linux Installation: desktop Other machines on which program tested: Compaq running True64 Unix Programming language used: Fortran 90 High speed storage required: case dependent No. of lines in distributed program, including test data, etc.: 1214 No. of bytes in distributed program, including test data, etc.: 9361 Distribution format: gz Keywords: Expectation values, Hellmann-Feynman theorem, potential fitting Has code been vectorised or parallelised?: The code has been extensively vectorised Nature of physical problem: XPECT3 calculates expectation of geometrically defined operators using previously calculated wavefunctions Method of solution: Integrals over the user defined surfaces are constructed using a DVR in all three coordinates. Wavefunctions generated by DVR3DRJZ and ROTLEV3 or ROTLEV3B are then used to give expectation values for each state Restrictions on the complexity of the problem: The complexity of problem that can be solved by DVR3DRJZ, ROTLEV3 or ROTLEV3B Typical running time: Case dependent. The test data takes a few seconds on a fast PC Unusual features of the program: Most data is read directly from DVR3DRJZ and ROTLEV3 or ROTLEV3B.
NASA Astrophysics Data System (ADS)
Grf, M.; Polovkov, J.; Gatial, A.; Milata, V.; ?ernuchov, P.; Prnayov, N.; Mat?jka, P.
2007-05-01
The isomers and conformers of two push-pull hydrazines: 3- N, N-dimethylhydrazino-2-acetyl propenenitrile [(H 3C) 2N sbnd NH sbnd CH dbnd C(CN)(COCH 3)] (DMHAP) and 3- N, N-dimethylhydrazino-2-methylsulfonyl propenenitrile [(H 3C) 2N sbnd NH sbnd CH dbnd C(CN)(SO 2CH 3)] (DMHSP) have been studied experimentally by NMR and vibrational spectroscopy and theoretically by the ab initio calculations at MP2 level in 6-31G** basis set. The IR and Raman spectra of both compounds as a solid and solute in various solvents have been recorded. The NMR spectra were obtained in chloroform and DMSO at room temperature. Both compounds have been prepared by the same way. NMR spectra revealed that DMHAP was prepared as a pure Z-isomer whereas in the case of DMHSP a pure E-isomer was obtained. Due to the low barrier for both compounds practically free isomerisation process occurred in the solutions but in opposite directions. Whereas DMHAP exists in the solid state and in the less polar solvent as Z-isomer, in more polar solvents the appearance of next two conformers of E-isomer was observed. On the contrary DMHSP exists in the solid state and in the more polar solvent as E-isomer only but in less polar solvent the presence of Z-isomer was observed as well. Conformational possibilities of both studied compounds are given by the rotation of dimethylhydrazino group with its anti- or syn-orientation towards the olefinic double bond. Moreover, by the rotation of the acetyl group with Z- and E-orientation of carbonyl bond towards olefinic double bond can occur in DMHAP. Vibrational and NMR spectra revealed the existence of single conformer with intramolecular hydrogen bond for Z-isomer in less polar solvent and next two conformers for E-isomer of DMHAP with Z-orientation of acetyl group and anti and syn orientation of dimethylhydrazine group in more polar solvents. For E-isomer of DMHSP two conformers with anti or syn orientations of dimethylhydrazino group have been also confirmed by NMR spectra in more polar solvents. Additionally the third DMHSP conformer with anti orientation of dimethylhydrazino group originating from Z-isomer was detected in less polar solvents. These experimental findings have been supported by ab initio calculations with solvent effect inclusion.
NASA Astrophysics Data System (ADS)
Lopez-Pieiro, A.; Sanchez, M. L.; Moreno, B.
1992-06-01
The computer program MORSMATEL has been developed to calculate vibrational-rotational matrix elements of several r-dependent operators of two Morse oscillators. This code is based on a set of recurrence relations which are valid for any value of the power and of the quantum numbers v and J of each oscillator.
NASA Technical Reports Server (NTRS)
Wanser, K. H.
1981-01-01
Silicon has interesting harmonic and anharmonic properties such as the low lying transverse acoustic modes at the X and L points of the Brillouin zone, negative Gruneisen parameters, negative thermal expansion and anomalous acoustic attenuation. In an attempt to understand these properties, a lattice dynamical model employing long range, nonlocal, dipole-dipole interactions was developed. Analytic expression for the Gruneisen parameters of several modes are presented. These expressions explain how the negative Gruneisen parameters arise. This model is applied to the calculation of the thermal expansion of silicon from 5K to 1700K. The thermoelastic contribution to the acoustic attenuation of silicon is computed from 1 to 300 K. Strong attenuation anomalies associated with negative thermal expansion are found in the vicinity of 17K and 125K.
Joseph, Lynnette; Sajan, D; Chaitanya, K; Isac, Jayakumary
2014-03-25
The conformational behavior and structural stability of trans-1,2-bis(3,5-dimethoxy phenyl)-ethene (TDBE) were investigated by using density functional theory (DFT) method with the B3LYP/6-311++G(d,p) basis set combination. The vibrational wavenumbers of TDBE were computed at DFT level and complete vibrational assignments were made on the basis of normal coordinate analysis calculations (NCA). The DFT force field transformed to natural internal coordinates was corrected by a well-established set of scale factors that were found to be transferable to the title compound. The infrared and Raman spectra were also predicted from the calculated intensities. The observed Fourier transform infrared (FTIR) and Fourier transform (FT) Raman vibrational wavenumbers were analyzed and compared with the theoretically predicted vibrational spectra. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential surfaces (ESP). PMID:24317264
Chakraborty, Indrani; Shirodkar, Sharmila N; Gohil, Smita; Waghmare, Umesh V; Ayyub, Pushan
2014-01-15
We report the optical, electronic, vibrational and mechanical properties of a stable, anisotropic, hexagonal (4H) form of silver. First principles calculations based on density functional theory were used to simulate the phonon dispersion curves and electronic band structure of 4H-Ag. The phonon dispersion data at 0 K do not contain unstable phonon modes, thereby confirming that it is a locally stable structure. The Fermi surface of the 4H phase differs in a subtle way from that of the cubic phase. Experimental measurements indicate that, when compared to the commonly known face-centered cubic (3C) form of silver, the 4H-Ag form shows a 130-fold higher, strongly anisotropic, in-plane resistivity and a much lower optical reflectance with a pronounced surface plasmon contribution that imparts a distinctive golden hue to the material. Unlike common silver, the lower symmetry of the 4H-Ag structure allows it to be Raman active. Mechanically, 4H-Ag is harder, more brittle and less malleable. Overall, this novel, poorly metallic, anisotropic, darker and harder crystallographic modification of silver bears little resemblance to its conventional counterpart. PMID:24305516
NASA Astrophysics Data System (ADS)
Lin, Y.-S.; Pieniazek, P. A.; Yang, Mino; Skinner, J. L.
2010-05-01
Polarization-resolved vibrational pump-probe experiments are useful for measuring the dynamics of molecular reorientation. The rotational anisotropy observable is usually modeled by the second-Legendre-polynomial time-correlation function of the appropriate molecule-fixed unit vector. On the other hand, more elaborate calculations that include non-Condon effects, excited-state absorption, and spectral diffusion, can be performed using the infrastructure of the nonlinear response formalism. In this paper we present "exact" (within the impulsive limit) results from the nonlinear response formalism, and also a series of approximations that ultimately recover the traditional result mentioned above. To ascertain the importance of these effects not included in the traditional approach, we consider the specific case of dilute HOD in H2O. We find that for the frequency-integrated anisotropy decay, it is important to include non-Condon effects. For the frequency-resolved anisotropy decay, non-Condon effects, excited-state absorption, and spectral diffusion are all important. We compare our results with recent experiments.
Ashizawa, Ryota; Noguchi, Takumi
2014-06-28
The effects of H-bonding on the redox potential and molecular vibrations of plastoquinone (PQ) that functions as a primary and a secondary quinone electron acceptor (QA and QB, respectively) in photosystem II (PSII) in plants and cyanobacteria were investigated using density functional theory calculations. Calculations were performed on the neutral and semiquinone anion forms of PQ and its H-bonded complexes, which form H-bonds with water molecules, or using amino acid models mimicking the interactions of QA and QB. The calculated redox potential (E(o)) of PQ showed a linear relationship with the number of H-bonds, and the E(o) increased by +100-200 mV with the addition of one H-bond. Vibrational analysis of the model PQ complexes showed that the CO stretching vibrations of neutral PQ are sensitive to the number and symmetry of H-bonding interactions, providing criteria to determine the H-bonding structure. Although no specific trend in the H-bonding dependency was found for anionic PQ, complex spectral features in the CO stretching region due to significant couplings with other PQ vibrations and the vibrations of H-bonding amino acids are useful monitors of the change in the H-bonding structure of anionic PQ in proteins. The calculated E(o) values and infrared spectra of the QA and QB models are consistent with the view that one additional H-bond to QB from D1-Ser264 largely contributes to the redox potential gap between QA and QB in PSII. PMID:24448716
Halverson, Thomas Poirier, Bill
2014-05-28
Exact quantum dynamics calculations of vibrational spectra are performed for two molecular systems of widely varying dimensionality (P{sub 2}O and CH{sub 2}NH), using a momentum-symmetrized Gaussian basis. This basis has been previously shown to defeat exponential scaling of computational cost with system dimensionality. The calculations were performed using the new SWITCHBLADE black-box code, which utilizes both dimensionally independent algorithms and massive parallelization to compute very large numbers of eigenstates for any fourth-order force field potential, in a single calculation. For both molecules considered here, many thousands of vibrationally excited states were computed, to at least an intermediate level of accuracy (tens of wavenumbers). Future modifications to increase the accuracy to spectroscopic levels, along with other potential future improvements of the new code, are also discussed.
Miliordos, Evangelos; Aprà, Edoardo; Xantheas, Sotiris S
2013-09-21
We report the first optimum geometries and harmonic vibrational frequencies for the ring pentamer and several water hexamer (prism, cage, cyclic and two book) at the coupled-cluster including single, double, and full perturbative triple excitations (CCSD(T))/aug-cc-pVDZ level of theory. All five examined hexamer isomer minima previously reported by Møller-Plesset perturbation theory (MP2) are also minima on the CCSD(T) potential energy surface (PES). In addition, all CCSD(T) minimum energy structures for the n = 2-6 cluster isomers are quite close to the ones previously obtained by MP2 on the respective PESs, as confirmed by a modified Procrustes analysis that quantifies the difference between any two cluster geometries. The CCSD(T) results confirm the cooperative effect of the homodromic ring networks (systematic contraction of the nearest-neighbor (nn) intermolecular separations with cluster size) previously reported by MP2, albeit with O-O distances shorter by ~0.02 Å, indicating that MP2 overcorrects this effect. The harmonic frequencies at the minimum geometries were obtained by the double differentiation of the CCSD(T) energy using an efficient scheme based on internal coordinates that reduces the number of required single point energy evaluations by ~15% when compared to the corresponding double differentiation using Cartesian coordinates. Negligible differences between MP2 and CCSD(T) frequencies are found for the librational modes, while uniform increases of ~15 and ~25 cm(-1) are observed for the bending and "free" OH harmonic frequencies. The largest differences between CCSD(T) and MP2 are observed for the harmonic hydrogen bonded frequencies, for which the former produces larger absolute values than the latter. Their CCSD(T) redshifts from the monomer values (Δω) are smaller than the MP2 ones, due to the fact that CCSD(T) produces shorter elongations (ΔR) of the respective hydrogen bonded OH lengths from the monomer value with respect to MP2. Both the MP2 and CCSD(T) results for the hydrogen bonded frequencies were found to closely follow the relation -Δω = s · ΔR, with a rate of s = 20.2 cm(-1)/0.001 Å for hydrogen bonded frequencies with IR intensities >400 km/mol. The CCSD(T) harmonic frequencies, when corrected using the MP2 anharmonicities obtained from second order vibrational perturbation theory, produce anharmonic CCSD(T) estimates that are within <60 cm(-1) from the measured infrared (IR) active bands of the n = 2-6 clusters. Furthermore, the CCSD(T) harmonic redshifts (with respect to the monomer) trace the measured ones quite accurately. The energetic order between the various hexamer isomers on the PES (prism has the lowest energy) previously reported at MP2 was found to be preserved at the CCSD(T) level, whereas the inclusion of anharmonic corrections further stabilizes the cage among the hexamer isomers. PMID:24070285
NASA Astrophysics Data System (ADS)
Miliordos, Evangelos; Aprà, Edoardo; Xantheas, Sotiris S.
2013-09-01
We report the first optimum geometries and harmonic vibrational frequencies for the ring pentamer and several water hexamer (prism, cage, cyclic and two book) at the coupled-cluster including single, double, and full perturbative triple excitations (CCSD(T))/aug-cc-pVDZ level of theory. All five examined hexamer isomer minima previously reported by Møller-Plesset perturbation theory (MP2) are also minima on the CCSD(T) potential energy surface (PES). In addition, all CCSD(T) minimum energy structures for the n = 2-6 cluster isomers are quite close to the ones previously obtained by MP2 on the respective PESs, as confirmed by a modified Procrustes analysis that quantifies the difference between any two cluster geometries. The CCSD(T) results confirm the cooperative effect of the homodromic ring networks (systematic contraction of the nearest-neighbor (nn) intermolecular separations with cluster size) previously reported by MP2, albeit with O-O distances shorter by ˜0.02 Å, indicating that MP2 overcorrects this effect. The harmonic frequencies at the minimum geometries were obtained by the double differentiation of the CCSD(T) energy using an efficient scheme based on internal coordinates that reduces the number of required single point energy evaluations by ˜15% when compared to the corresponding double differentiation using Cartesian coordinates. Negligible differences between MP2 and CCSD(T) frequencies are found for the librational modes, while uniform increases of ˜15 and ˜25 cm-1 are observed for the bending and "free" OH harmonic frequencies. The largest differences between CCSD(T) and MP2 are observed for the harmonic hydrogen bonded frequencies, for which the former produces larger absolute values than the latter. Their CCSD(T) redshifts from the monomer values (Δω) are smaller than the MP2 ones, due to the fact that CCSD(T) produces shorter elongations (ΔR) of the respective hydrogen bonded OH lengths from the monomer value with respect to MP2. Both the MP2 and CCSD(T) results for the hydrogen bonded frequencies were found to closely follow the relation -Δω = s . ΔR, with a rate of s = 20.2 cm-1/0.001 Å for hydrogen bonded frequencies with IR intensities >400 km/mol. The CCSD(T) harmonic frequencies, when corrected using the MP2 anharmonicities obtained from second order vibrational perturbation theory, produce anharmonic CCSD(T) estimates that are within <60 cm-1 from the measured infrared (IR) active bands of the n = 2-6 clusters. Furthermore, the CCSD(T) harmonic redshifts (with respect to the monomer) trace the measured ones quite accurately. The energetic order between the various hexamer isomers on the PES (prism has the lowest energy) previously reported at MP2 was found to be preserved at the CCSD(T) level, whereas the inclusion of anharmonic corrections further stabilizes the cage among the hexamer isomers.
NASA Astrophysics Data System (ADS)
Petrenko, Taras; Neese, Frank
2012-12-01
In this work, an improved method for the efficient automatic simulation of optical band shapes and resonance Raman (rR) intensities within the "independent mode displaced harmonic oscillator" is described. Despite the relative simplicity of this model, it is able to account for the intensity distribution in absorption (ABS), fluorescence, and rR spectra corresponding to strongly dipole allowed electronic transitions with high accuracy. In order to include temperature-induced effects, we propose a simple extension of the time dependent wavepacket formalism developed by Heller which enables one to derive analytical expressions for the intensities of hot bands in ABS and rR spectra from the dependence of the wavepacket evolution on its initial coordinate. We have also greatly optimized the computational procedures for numerical integration of complicated oscillating integrals. This is important for efficient simulations of higher-order rR spectra and excitation profiles, as well as for the fitting of experimental spectra of large molecules. In particular, the multimode damping mechanism is taken into account for efficient reduction of the upper time limit in the numerical integration. Excited state energy gradient as well as excited state geometry optimization calculations are employed in order to determine excited state dimensionless normal coordinate displacements. The gradient techniques are highly cost-effective provided that analytical excited state derivatives with respect to nuclear displacements are available. Through comparison with experimental spectra of some representative molecules, we illustrate that the gradient techniques can even outperform the geometry optimization method if the harmonic approximation becomes inadequate.
NASA Astrophysics Data System (ADS)
Zhou, Sarah Xiaohua; Durig, James R.
2009-04-01
The infrared (3500-300 cm -1) and/or Raman (3500-50 cm -1) spectra of gaseous, liquid and solid of methylisocyanate, CH 3NCO, have been recorded. Fine structures of the nearly free internal rotation of the methyl rotor has been observed for the pseudodegenerate CH 3 stretch and deformation from which the band centers and Coriolis coupling constants have been determined. Ab initio calculations with full electron correlation by the perturbation method to second order and hybrid density functional theory calculations by the B3LYP method utilizing the 6-31G(d), 6-311+G(d,p), and 6-311+G(2d,2p) basis sets have been carried out. From these calculations, force constants, vibrational frequencies, infrared intensities, Raman activities, depolarization ratios, and structural parameters have been determined and compared to the experimental quantities. Several differences are noted between the predicted and experimental values. By combining the three previously reported rotational constants for CH 3NCO with the ab initio MP2/6-311+G(d,p) predicted structural values, adjusted r0 parameters have been obtained. The r0 values for the distance (Å) are: r(C dbnd N) = 1.447(3); r(N dbnd C) = 1.215(3); r(C dbnd O) = 1.166(3); r(C sbnd H a) = 1.089(2); r(C sbnd H s) = 1.093(2), and for the angles (degrees): ∠CNC=135.8(5); ∠NCO=172.6(5); ∠NCH=108.6(5); ∠NCH=110.8(5). Several of these parameters are significantly different from those previously reported from the latest microwave study. Predicted barriers to internal rotation and linearity as well as values of the centrifugal distortion constants are given and compared to experimental values when available. The results of these spectroscopic and theoretical studies are discussed and compared to the corresponding results of some similar molecules.
Attaccalite, C; Nguer, A; Cannuccia, E; Grning, M
2015-04-14
The second harmonic generation (SHG) intensity spectrum of SiC, ZnO, GaN two-dimensional hexagonal crystals is calculated by using a real-time first-principles approach based on Green's function theory [Attaccalite et al., Phys. Rev. B: Condens. Matter Mater. Phys. 2013 88, 235113]. This approach allows one to go beyond the independent particle description used in standard first-principles nonlinear optics calculations by including quasiparticle corrections (by means of the GW approximation), crystal local field effects and excitonic effects. Our results show that the SHG spectra obtained using the latter approach differ significantly from their independent particle counterparts. In particular they show strong excitonic resonances at which the SHG intensity is about two times stronger than within the independent particle approximation. All the systems studied (whose stabilities have been predicted theoretically) are transparent and at the same time exhibit a remarkable SHG intensity in the range of frequencies at which Ti:sapphire and Nd:YAG lasers operate; thus they can be of interest for nanoscale nonlinear frequency conversion devices. Specifically the SHG intensity at 800 nm (1.55 eV) ranges from about 40-80 pm V(-1) in ZnO and GaN to 0.6 nm V(-1) in SiC. The latter value in particular is 1 order of magnitude larger than values in standard nonlinear crystals. PMID:25766901
NASA Technical Reports Server (NTRS)
Zhang, Y. C.; Zhang, J. Z. H.; Kouri, D. J.; Haug, K.; Schwenke, D. W.
1988-01-01
Numerically exact, fully three-dimensional quantum mechanicl reactive scattering calculations are reported for the H2Br system. Both the exchange (H + H-prime Br to H-prime + HBr) and abstraction (H + HBR to H2 + Br) reaction channels are included in the calculations. The present results are the first completely converged three-dimensional quantum calculations for a system involving a highly exoergic reaction channel (the abstraction process). It is found that the production of vibrationally hot H2 in the abstraction reaction, and hence the extent of population inversion in the products, is a sensitive function of initial HBr rotational state and collision energy.
Espinosa-Garcia, Joaquin; Corchado, Jose C
2016-03-01
For the OH + CH4/CD4 hydrogen abstraction reactions, the methyl radical (CH3 and CD3) product translational distributions and the water (H2O and HOD) product vibrational distributions experimentally reported by Liu's group are reproduced by quasi-classical trajectory (QCT) calculations on an analytical full-dimensional potential energy surface when a quantum spirit is included in the analysis. Our simulations correctly predict: (i) the vibrational excitation of the water product, (ii) the inversion of the water vibrational population, and (iii) the propensity of transfer from reactant kinetic energy to product translational energy. These reactions therefore present a marked isotopic effect. In addition, the water product vibrational distributions for the OH/OD + CH4 reactions agree reasonably well with Butkovskaya and Setser's experiments for a similar alkane reaction. The theory/experiment agreement is better for the HOD than for the H2O product due to the mode coupling in the H2O molecule, which is absent in the HOD stretching modes, which show a more "local" character. In summary, for polyatomic systems with many degrees of freedom (15 in the present reaction), QCT calculations analyzed with a quantum spirit represent a useful alternative to quantum scattering methods. PMID:26061483
Teimouri, Abbas; Chermahini, Alireza Najafi; Taban, Keivan; Dabbagh, Hossein A
2009-03-01
The detailed experimental and computational analysis [Hartree-Fock (HF), Time-Dependent Density-Functional Theory (TD-DFT) and Second-Order Mller-Plesset Perturbation Theory (PM2) levels of theory at standard 6-31G* basis set] of structure, infrared spectra and visible spectra of azo dyes are investigated. The optimized geometries and calculated vibrational frequencies are evaluated via comparison with experimental values. The vibrational spectral data obtained from solid phase FT-IR spectra are assigned based on the results of the theoretical calculations. The observed spectra are found to be in good agreement with the calculated values. The geometry optimization yields a planar conformation for phenyl rings with azo moiety. The energy and oscillator strength calculated by Configuration Interaction Singles (CIS) complements the Time-Dependent Density-Functional Theory (TD-DFT) results and the experimental findings. Unfortunately, PM2 method could not predict vibrational frequencies and visible spectra of the azo dyes under conditions of this investigation. PMID:19042151
NASA Astrophysics Data System (ADS)
Sarma, Manabendra; Adhikari, S.; Mishra, Manoj K.
2007-01-01
Vibrational excitation (?f??i) cross-sections ??f??i(E) in resonant e-N2 and e-H2 scattering are calculated from transition matrix elements T?f,?i(E ) obtained using Fourier transform of the cross correlation function ???f(R)???i(R,t)?, where ??i(R,t)?e-iHA2-(R)t/???i(R) with time evolution under the influence of the resonance anionic Hamiltonian HA2-(A2-=N2-/H2-) implemented using Lanczos and fast Fourier transforms. The target (A2) vibrational eigenfunctions ??i(R) and ??f(R) are calculated using Fourier grid Hamiltonian method applied to potential energy (PE) curves of the neutral target. Application of this simple systematization to calculate vibrational structure in e-N2 and e-H2 scattering cross-sections provides mechanistic insights into features underlying presence/absence of structure in e-N2 and e-H2 scattering cross-sections. The results obtained with approximate PE curves are in reasonable agreement with experimental/calculated cross-section profiles, and cross correlation functions provide a simple demarcation between the boomerang and impulse models.
Nogueira, C E S; Caselli, P E S; Freire, P T C; Teixeira, A M R; Oliveira, I M M; Bento, R R F; Faria, J L B; Gusmo, G O M; Silva, L E
2015-10-01
In this work we present a study of the vibrational spectra of 4,5,6,8,9-pentachloropyrimido-[1,2-a][1,8]naphthyridin-10-one, C11H2Cl5N3O, a substance belonging to the important pharmacological class of 1,8-naphthyridine derivatives. The Fourier transform infrared and the Fourier transform Raman spectra of the crystal were recorded at room temperature in the regions 400-4000 and 50-4000 cm(-1), respectively. Vibrational wavenumbers were predicted using Density Functional Theory calculations with the B3LYP functional on 6-31G(d,p) and 6-311++G(d,p) basis sets. The descriptions of the normal modes were made after calculating the potential energy distribution. Additionally, potential reaction sites were evaluated through Mulliken population and Frontier Orbital analysis. PMID:25965513
NASA Astrophysics Data System (ADS)
Bubin, Sergiy; Stanke, Monika; Adamowicz, Ludwik
2014-04-01
Very accurate variational calculations of the complete pure vibrational spectrum of the ditritium (T2) molecule are performed within the framework where the Born-Oppenheimer approximation is not assumed. After separating out the center-of-mass motion from the total laboratory-frame Hamiltonian, T2 becomes a three-particle problem. States corresponding to the zero total angular momentum, which are pure vibrational states, are spherically symmetric in this framework. The wave functions of these states are expanded in terms of all-particle, one-center, spherically symmetric explicitly correlated Gaussian functions multiplied by even non-negative powers of the internuclear distance. In the calculations the total energies, the dissociation energies, and expectation values of some operators dependent on interparticle distances are determined.
NASA Astrophysics Data System (ADS)
Joshi, Bhawani Datt; Srivastava, Anubha; Tandon, Poonam; Jain, Sudha
2011-11-01
Yohimbine hydrochloride (YHCl) is an aphrodisiac and promoted for erectile dysfunction, weight loss and depression. The optimized geometry, total energy, potential energy surface and vibrational wavenumbers of yohimbine hydrochloride have been determined using ab initio, Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method with 6-311++G(d,p) basis set. A complete vibrational assignment is provided for the observed Raman and IR spectra of YHCl. The UV absorption spectrum was examined in ethanol solvent and compared with the calculated one in gas phase as well as in solvent environment (polarizable continuum model, PCM) using TD-DFT/6-31G basis set. These methods are proposed as a tool to be applied in the structural characterization of YHCl. The calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) with frontier orbital gap are presented.
Hu, Tao; Wang, Jiemin; Zhang, Hui; Li, Zhaojin; Hu, Minmin; Wang, Xiaohui
2015-04-21
We present a comparative study on the static and dynamical properties of bare Ti3C2 and T-terminated Ti3C2T2 (T = O, F, OH) monosheets using density functional theory calculations. First, the crystal structures are optimized to be of trigonal configurations (P3[combining macron]m1), which are thermodynamically and dynamically stable. It is demonstrated that the terminations modulate the crystal structures through valence electron density redistribution of the atoms, particularly surface Ti (Ti2) in the monosheets. Second, lattice dynamical properties including phonon dispersion and partial density of states (PDOS) are investigated. Phonon PDOS analysis shows a clear collaborative feature in the vibrations, reflecting the covalent nature of corresponding bonds in the monosheets. In the bare Ti3C2 monosheet, there is a phonon band gap between 400 and 500 cm(-1), while it disappears in Ti3C2O2 and Ti3C2(OH)2 as the vibrations associated with the terminal atoms (O and OH) bridge the gap. Third, both Raman (Eg and A1g) and infrared-active (Eu and A2u) vibrational modes are predicted and conclusively assigned. A comparative study indicates that the terminal atoms remarkably influence the vibrational frequencies. Generally, the terminal atoms weaken the vibrations in which surface Ti atoms are involved while strengthening the out-of-plane vibration of C atoms. Temperature-dependent micro Raman measurements agree with the theoretical prediction if the complexity in the experimentally obtained lamellae for the Raman study is taken into account. PMID:25785395
NASA Technical Reports Server (NTRS)
Hedgepeth, John M.; Warner, Paul G., Jr.
1959-01-01
Generalized influence coefficients are calculated by the method of NACA TN 3640 for a large-scale, built-up, 450 delta-wing specimen. These are used together with appropriate generalized masses to obtain the natural modes and frequencies in symmetric and antisymmetric free-free vibration. The resulting frequencies are compared with those obtained experimentally and are found to be consistently high. Possible sources of the disparities are discussed.
Premkumar, S; Jawahar, A; Mathavan, T; Kumara Dhas, M; Milton Franklin Benial, A
2015-03-01
The vibrational spectra of 2-amino-7-bromo-5-oxo-[1]benzopyrano [2,3-b]pyridine-3 carbonitrile were recorded using fourier transform-infrared and fourier transform-Raman spectrometer. The optimized structural parameters, vibrational frequencies, Mulliken atomic charge distribution, frontier molecular orbitals, thermodynamic properties, temperature dependence of thermodynamic parameters, first order hyperpolarizability and natural bond orbital calculations of the molecule were performed using the Gaussian 09 program. The vibrational frequencies were assigned on the basis of potential energy distribution calculation using the VEDA 4.0 program. The calculated first order hyperpolarizability of ABOBPC molecule was obtained as 6.90810(-30) issue, which was 10.5 times greater than urea. The nonlinear optical activity of the molecule was also confirmed by the frontier molecular orbitals and natural bond orbital analysis. The frontier molecular orbitals analysis shows that the lower energy gap of the molecule, which leads to the higher value of first order hyperpolarizability. The natural bond orbital analysis indicates that the nonlinear optical activity of the molecule arises due to the ???(?) transitions. The Mulliken atomic charge distribution confirms the presence of intramolecular charge transfer within the molecule. The reactive site of the molecule was predicted from the molecular electrostatic potential contour map. The values of thermo dynamic parameters were increasing with increasing temperature. PMID:25498822
NASA Astrophysics Data System (ADS)
Manzoor Ali, M.; George, Gene; Ramalingam, S.; Periandy, S.; Gokulakrishnan, V.
2015-11-01
In this research work, in order to the vibrational, physical and chemical properties, a thorough investigation has been made by recording FT-IR, FT-Raman, Mass and 13C and 1H NMR spectra of pharmaceutically important compound; 3,6-Dimethylphenanthrene. The altered geometrical parameters of Phenanthrene due to the addition of methyl groups have been calculated using HF and DFT (B3LYP and B3PW91) methods with 6-31++G(d,p) and 6-311++G(d,p) basis sets and the discussion are made on their corresponding results. The alternation of the vibrational pattern of the molecule due to the injection of the substitutions; CH3 is investigated. The keen observation is made over the excitations between the electronic energy levels of the molecule which lead to the study of electronic properties. The alternation of distribution of Mulliken charges after the formation of present molecule has been correlated with the vibrational pattern of the molecular bonds. The charge transformation over the frontier molecular orbitals between the ligand and rings has been studied. The cause of the linear and non linear optical activity of the molecule is interpreted in detail from the average Polarizability first order diagonal hyperpolarizability calculations. The variation of thermodynamic properties; heat capacity, entropy, and enthalpy of the present compound at different temperatures are calculated using NIST thermodynamical function program and interpreted.
NASA Astrophysics Data System (ADS)
Premkumar, S.; Jawahar, A.; Mathavan, T.; Kumara Dhas, M.; Milton Franklin Benial, A.
2015-03-01
The vibrational spectra of 2-amino-7-bromo-5-oxo-[1]benzopyrano [2,3-b]pyridine-3 carbonitrile were recorded using fourier transform-infrared and fourier transform-Raman spectrometer. The optimized structural parameters, vibrational frequencies, Mulliken atomic charge distribution, frontier molecular orbitals, thermodynamic properties, temperature dependence of thermodynamic parameters, first order hyperpolarizability and natural bond orbital calculations of the molecule were performed using the Gaussian 09 program. The vibrational frequencies were assigned on the basis of potential energy distribution calculation using the VEDA 4.0 program. The calculated first order hyperpolarizability of ABOBPC molecule was obtained as 6.908 10-30 issue, which was 10.5 times greater than urea. The nonlinear optical activity of the molecule was also confirmed by the frontier molecular orbitals and natural bond orbital analysis. The frontier molecular orbitals analysis shows that the lower energy gap of the molecule, which leads to the higher value of first order hyperpolarizability. The natural bond orbital analysis indicates that the nonlinear optical activity of the molecule arises due to the ? ? ?? transitions. The Mulliken atomic charge distribution confirms the presence of intramolecular charge transfer within the molecule. The reactive site of the molecule was predicted from the molecular electrostatic potential contour map. The values of thermo dynamic parameters were increasing with increasing temperature.
Suvitha, A; Periandy, S; Boomadevi, S; Govindarajan, M
2014-01-01
In this work, the vibrational spectral analysis is carried out by using Raman and infrared spectroscopy in the range 100-4000 cm(-1)and 50-4000 cm(-1), respectively, for pycolinaldehyde oxime (PAO) (C6H6N2O) molecule. The vibrational frequencies have been calculated and scaled values are compared with experimental FT-IR and FT-Raman spectra. The structure optimizations and normal coordinate force field calculations are based on HF and B3LYP methods with 6-311++G(d,p) basis set. The results of the calculation shows excellent agreement between experimental and calculated frequencies in B3LYP/6-311++G(d,p) basis set. The optimized geometric parameters are compared with experimental values of PAO. The non linear optical properties, NBO analysis, thermodynamics properties and mulliken charges of the title molecule are also calculated and interpreted. A study on the electronic properties, such as HOMO and LUMO energies, are performed by time-dependent DFT (TD-DFT) approach. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) are performed. The effects due to the substitutions of CH=NOH ring are investigated. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule are calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. PMID:23994677
NASA Astrophysics Data System (ADS)
Krishna Kumar, V.; Suganya, S.; Mathammal, R.
This work deals with the vibrational spectra of 2,3,4,5,6-Penta Bromo Toluene (PBT) and Bromo Durene (BD) by quantum chemical calculations. The solid phase FTIR and FT-Raman spectra of the title compounds were recorded in the regions 4000-400 cm-1 and 4000-50 cm-1, respectively. The spectra were interpreted with the aid of normal coordinate analysis based on density functional theory (DFT) using B3LYP/6-31G? level and basis set combinations and was scaled using various scale factors yielding a good agreement between observed and calculated frequencies. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. The HOMO and LUMO energies were calculated within the molecule. 13C and 1H NMR chemical shifts results were also calculated and compared with the experimental values. Thermodynamical properties like entropy heat capacity, zero point energy have been calculated for the title molecules.
A formulation of rotor-airframe coupling for design analysis of vibrations of helicopter airframes
NASA Technical Reports Server (NTRS)
Kvaternik, R. G.; Walton, W. C., Jr.
1982-01-01
A linear formulation of rotor airframe coupling intended for vibration analysis in airframe structural design is presented. The airframe is represented by a finite element analysis model; the rotor is represented by a general set of linear differential equations with periodic coefficients; and the connections between the rotor and airframe are specified through general linear equations of constraint. Coupling equations are applied to the rotor and airframe equations to produce one set of linear differential equations governing vibrations of the combined rotor airframe system. These equations are solved by the harmonic balance method for the system steady state vibrations. A feature of the solution process is the representation of the airframe in terms of forced responses calculated at the rotor harmonics of interest. A method based on matrix partitioning is worked out for quick recalculations of vibrations in design studies when only relatively few airframe members are varied. All relations are presented in forms suitable for direct computer implementation.
Self-mixing interference signal analysis based on Fourier transform method for vibration measurement
NASA Astrophysics Data System (ADS)
Huang, Zhen; Sun, Xiaogang; Li, Chengwei
2013-05-01
An algorithm for analyzing a vibrating target by a dominant harmonic order determination based on Fourier transform in a self-mixing system over wide optical feedback regimes (very weak, weak, and moderate regimes) is presented. The basic frequency of a self-mixing interference signal is used to determine the frequency of vibration, and the dominant harmonic order is proportional to the amplitude of vibration. The algorithm also allows calculation of the correct target movement at extremely low signal-to-noise ratios. The validity of the proposed algorithm was demonstrated by means of simulated signals and confirmed by several experimental measurements. The maximum error of the amplitude is about 0.16 ?m and the maximum error of the frequency is about 2.5%. It can be used to demodulate the microscopic vibration of a remote target.
Zhang, Lijuan; Liu, Sheng; Cheng, Min; Du, Yikui; Zhu, Qihe
2016-01-14
The mass-analyzed threshold ionization spectra of jet-cooled cis- and trans-3-fluoro-N-methylaniline (3FNMA) were recorded by ionizing via the vibrationless 0(0) and various vibrational levels of the S1 state. The adiabatic ionization energies of cis- and trans-3FNMA are determined to be 61?742 5 and 61?602 5 cm(-1), respectively. In the 0-1800 cm(-1) region, most of the observed vibrations in the D0 state result from the in-plane ring deformation and substituent-sensitive modes. For the high-frequency vibration region, the infrared-ultraviolet double-resonance and autoionization-detected infrared spectroscopies were applied to investigate the N-H and C-H stretching vibrations of bare 3FNMA in the S0 and D0 states. The C-H stretching vibrational information, which we failed to obtain for the bare 3FNMA cation, is complemented by recording the infrared-photodissociation spectra of its Ar cluster cation. It is revealed that a red-shifted frequency and an enhanced intensity are observed for the N-H stretch, while blue-shifted frequencies and greatly decreased intensities are found for both aromatic and the methyl C-H stretches. The blue shift of the C-H stretches is first explained by the balance of two factors, namely, the hyperconjugative interaction and the rehybridization effect. Analysis of the vibrational frequencies reveals a correlation between the relative stability of two rotamers in different electronic states and the relative rigidity of aromatic ring, indicating a mechanism of the long-range interactions "through bond" between the substituents. The density functional theory calculations can well reproduce the vibrational spectra in both S0 and D0 states. With the experimental and theoretical data, the substitution and conformation effects on the properties of 3FNMA in the S0 and D0 states, including the molecular structures, the reactive sites of electrophilic attack, and the vibrational behaviors, were discussed in detail. PMID:26669268
NASA Astrophysics Data System (ADS)
Ben Hassen, C.; Boujelbene, M.; Marweni, S.; Bahri, M.; Mhiri, T.
2015-10-01
The present paper undertakes the study of a new organic/inorganic hybrid compound [2-CH3C6H4NH3]HSO4.H2O characterized by the X-ray diffraction, TG-DTA, IR and Raman spectroscopy accomplished with DFT calculation. It is crystallized in the monoclinic system with the centrosymmetric space group P 21/c, with a = 9.445 (5) Å, b = 10.499 Å, c = 10.073 Å, β = 90.627 (5)° and Z = 4. The atomic arrangement can be described as inorganic layers built by infinite chains, parallel to the (a c) planes between which the organic cations are inserted. In this atomic arrangement, hydrogen bonds and π-π interactions between the different species have an important role in the tri-dimensional network cohesion. Besides, the X-ray powder diffraction of the title compound confirms the existence of only one phase at room temperature. The thermal decomposition of precursors studied by thermo gravimetric analysis (TGA), the differential thermal analysis (DTA) and the temperature-dependent X-ray diffraction, show crystalline anhydrous compounds upon dehydration. DFT/BHHLYP calculations were performed, using the DZV (d,p) basis set, to determine the harmonic frequencies of the vibrational modes of an optimized cluster structure. The calculated modes were animated using the Molden graphical package to give tentative assignments of the observed IR and Raman spectra.
NASA Astrophysics Data System (ADS)
Cassam-Chena, P.; Rousseau, G.; Ilmane, A.; Bouret, Y.; Rey, M.
2015-07-01
In previous works, we have introduced an alternative perturbation scheme to find approximate solutions of the spectral problem for the rotation-vibration molecular Hamiltonian. An important feature of our approach is that the zero order Hamiltonian is the direct product of a purely vibrational Hamiltonian with the identity on the rotational degrees of freedom. The convergence of our method for the methane vibrational ground state was very satisfactory and our predictions were quantitative. In the present article, we provide further details on the implementation of the method in the degenerate and quasi-degenerate cases. The quasi-degenerate version of the method is tested on excited polyads of methane, and the results are assessed with respect to a variational treatment. The optimal choice of the size of quasi-degenerate spaces is determined by a trade-off between speed of convergence of the perturbation series and the computational effort to obtain the effective super-Hamiltonian.
NASA Technical Reports Server (NTRS)
Cross, R. J., Jr.
1979-01-01
A semiclassical approximation to treat vibrationally inelastic scattering is developed. The vibrational basis set used is adiabatic with respect to a reference potential which is chosen to be as close as possible to the true potential and also gives easily obtainable solutions to the vibrational wave equation. The radial wave functions are obtained using the WKB approximation, and the coupled Schroedinger equations are solved by a first-order perturbation method to yield a phase shift matrix which is exponentiated to give the full scattering matrix. Results were obtained for all the cases computed by Secrest and Johnson and by Clark and Dickinson, and the agreement is better than 10% for half of the cross-sections and rarely off by more than a factor of 2.
NASA Astrophysics Data System (ADS)
Carbonniere, Philippe; Pouchan, Claude
Computed anharmonic transitions and intensities of H2CN are reported in a spectral range ranging from 900 to 2,900 cm-1. Four vibrational treatments were considered from a B3LYP/6-31+G(d,p) potential electronic surface: The second order perturbational method, the full configuration interaction, the discrete variable representation method and the vibrational analysis arising from a molecular dynamics trajectory. The four approaches yield basically the same results since the convergence of the values is achieved by about 15-20 cm-1.
NASA Astrophysics Data System (ADS)
Horáček, J.; Čížek, M.; Houfek, K.; Kolorenč, P.; Domcke, W.
2004-11-01
An improved nonlocal resonance model proposed by Čížek, Horáček, and Domcke [J. Phys. B 31, 2571 (1998)] is used for the calculation of cross sections of electron dissociative attachment and vibrational excitation of molecular hydrogen by the impact of low-energy electrons in the range of Σu+2 resonance. The model is based on ab initio data and takes full account of the nonlocality of the effective potential for the nuclear motion. The dissociative attachment cross sections and rate constants are calculated for all target states (v,J) of relevance and compared with other theoretical and experimental data. It is found that the present dissociative attachment cross section calculated under the conditions of the experiment carried out by Schulz and Asundi reproduces the larger of the two values proposed by them, i.e.- 2.8×10-21cm2 . A detailed discussion of the dissociative attachment cross section as a function of the vibrational and rotational target states is given. Very narrow peaks, with a width of 1meV , are observed in the dissociative attachment cross section for large values of the orbital quantum number J . These structures are interpreted as shape resonances in H-+H collision dynamics. It is shown that for large values of J rotational excitation of the hydrogen molecule enhances the dissociative attachment more efficiently than vibrational excitation. The largest dissociative attachment cross section of 28.3×10-16cm2 is obtained for v=1 and J=29 . The process of vibrational excitation will be discussed in a separate paper.
Applications of higher harmonic control to hingeless rotor systems
NASA Technical Reports Server (NTRS)
Nguyen, Khanh; Chopra, Inderjit
1991-01-01
A comprehensive analytical formulation was developed to predict the vibratory hub loads of a helicopter rotor system in forward flight. This analysis is used to calculate the optimal higher harmonic control inputs and associated actuator power required to minimize these hub loads. The present formulation is based on a finite element method in space and time. A nonlinear time domain, unsteady aerodynamic model is used to obtain the airloads, and the rotor induced inflow is calculated using a nonuniform inflow model. Predicted vibratory hub loads are correlated with experimental data from a scale model rotor. Results of a parametric study on a hindgeless rotor show that blade flap, lag and torsion vibration characteristics, offset of blade center of mass from elastic axis, offset of elastic axis from quarter-chord axis, and blade thrust greatly affect the higher harmonic control actuator power requirement.
Homayoon, Zahra
2014-09-28
A new, full (nine)-dimensional potential energy surface and dipole moment surface to describe the NO{sup +}(H{sub 2}O) cluster is reported. The PES is based on fitting of roughly 32 000 CCSD(T)-F12/aug-cc-pVTZ electronic energies. The surface is a linear least-squares fit using a permutationally invariant basis with Morse-type variables. The PES is used in a Diffusion Monte Carlo study of the zero-point energy and wavefunction of the NO{sup +}(H{sub 2}O) and NO{sup +}(D{sub 2}O) complexes. Using the calculated ZPE the dissociation energies of the clusters are reported. Vibrational configuration interaction calculations of NO{sup +}(H{sub 2}O) and NO{sup +}(D{sub 2}O) using the MULTIMODE program are performed. The fundamental, a number of overtone, and combination states of the clusters are reported. The IR spectrum of the NO{sup +}(H{sub 2}O) cluster is calculated using 4, 5, 7, and 8 modes VSCF/CI calculations. The anharmonic, coupled vibrational calculations, and IR spectrum show very good agreement with experiment. Mode coupling of the water “antisymmetric” stretching mode with the low-frequency intermolecular modes results in intensity borrowing.
NASA Astrophysics Data System (ADS)
Kumar, J. Sharmi; Devi, T. S. Renuga; Ramkumaar, G. R.; Bright, A.
2016-01-01
The FTIR and FT-Raman spectra of 4-(2-Hydroxyethyl) piperazine-1-ethanesulfonic acid were recorded and the structural and spectroscopic data of the molecule in the ground state were calculated using Hartree-Fock and Density Functional Method (B3LYP). The most stable conformer was optimized and the structural and vibrational parameters were determined. With the observed FTIR and FT-Raman data, a complete vibrational band assignment and analysis of the fundamental modes of the compound were carried out. Thermodynamic properties, Mulliken and natural atomic charge distribution were calculated using both Hartree-Fock and Density Functional Method and compared. UV-Visible and HOMO-LUMO analysis were carried out. 1H and 13C NMR chemical shifts of the molecule were calculated using gauge including atomic orbital method and were compared with experimental results. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital analysis. The first order hyperpolarizability (?) and molecular electrostatic potential of the molecule was computed using DFT calculations. The electron density based local reactivity descriptor such as Fukui functions were calculated to explain the chemically reactive site in the molecule.
Kumar, J Sharmi; Devi, T S Renuga; Ramkumaar, G R; Bright, A
2016-01-01
The FTIR and FT-Raman spectra of 4-(2-Hydroxyethyl) piperazine-1-ethanesulfonic acid were recorded and the structural and spectroscopic data of the molecule in the ground state were calculated using Hartree-Fock and Density Functional Method (B3LYP). The most stable conformer was optimized and the structural and vibrational parameters were determined. With the observed FTIR and FT-Raman data, a complete vibrational band assignment and analysis of the fundamental modes of the compound were carried out. Thermodynamic properties, Mulliken and natural atomic charge distribution were calculated using both Hartree-Fock and Density Functional Method and compared. UV-Visible and HOMO-LUMO analysis were carried out. (1)H and (13)C NMR chemical shifts of the molecule were calculated using gauge including atomic orbital method and were compared with experimental results. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital analysis. The first order hyperpolarizability (?) and molecular electrostatic potential of the molecule was computed using DFT calculations. The electron density based local reactivity descriptor such as Fukui functions were calculated to explain the chemically reactive site in the molecule. PMID:26278882
Harmonic force field for nitro compounds.
Bellido, Edson P; Seminario, Jorge M
2012-06-01
Molecular simulations leading to sensors for the detection of explosive compounds require force field parameters that can reproduce the mechanical and vibrational properties of energetic materials. We developed precise harmonic force fields for alanine polypeptides and glycine oligopeptides using the FUERZA procedure that uses the Hessian tensor (obtained from ab initio calculations) to calculate precise parameters. In this work, we used the same procedure to calculate generalized force field parameters of several nitro compounds. We found a linear relationship between force constant and bond distance. The average angle in the nitro compounds was 116, excluding the 90 angle of the carbon atoms in the octanitrocubane. The calculated parameters permitted the accurate molecular modeling of nitro compounds containing many functional groups. Results were acceptable when compared with others obtained using methods that are specific for one type of molecule, and much better than others obtained using methods that are too general (these ignore the chemical effects of surrounding atoms on the bonding and therefore the bond strength, which affects the mechanical and vibrational properties of the whole molecule). PMID:22119786
McGuire, John Andrew
2004-11-24
The high temporal resolution and broad bandwidth of a femtosecond laser system are exploited in a pair of nonlinear optical studies of surfaces. The dephasing dynamics of resonances associated with the adatom dangling bonds of the Si(111)7 x 7 surface are explored by transient second-harmonic hole burning, a process that can be described as a fourth-order nonlinear optical process. Spectral holes produced by a 100 fs pump pulse at about 800 nm are probed by the second harmonic signal of a 100 fs pulse tunable around 800 nm. The measured spectral holes yield homogeneous dephasing times of a few tens of femtoseconds. Fits with a Lorentzian spectral hole centered at zero probe detuning show a linear dependence of the hole width on pump fluence, which suggests that charge carrier-carrier scattering dominates the dephasing dynamics at the measured excitation densities. Extrapolation of the deduced homogeneous dephasing times to zero excitation density yields an intrinsic dephasing time of {approx} 70 fs. The presence of a secondary spectral hole indicates that scattering of the surface electrons with surface optical phonons at 570 cm{sup -1} occurs within the first 200 fs after excitation. The broad bandwidth of femtosecond IR pulses is used to perform IR-visible sum frequency vibrational spectroscopy. By implementing a Fourier-transform technique, we demonstrate the ability to obtain sub-laser-bandwidth spectral resolution. FT-SFG yields a greater signal when implemented with a stretched visible pulse than with a femtosecond visible pulse. However, when compared with multichannel spectroscopy using a femtosecond IR pulse but a narrowband visible pulse, Fourier-transform SFG is found to have an inferior signal-to-noise ratio. A mathematical analysis of the signal-to-noise ratio illustrates the constraints on the Fourier-transform approach.
Kaindl, Reinhard; Sohr, Gerhard; Huppertz, Hubert
2013-12-01
The two oxoborates ?-ZnB4O7 and ?-CaB4O7 were synthesized and investigated by FTIR- and Raman spectroscopy and ab initio quantum chemical calculations. Maximum and mean deviations between experimentally determined bands and calculated modes ranged between 15-36 cm(-1) and 5-7 cm(-1), respectively, allowing band assignments to vibrational modes in most cases. The complex network structures with tetrahedral BO4 and planar OB3 groups are mirrored by the spectra and numerous vibrational modes, not assignable by standard borates classification schemes. It was confirmed that OB3 units, despite similar force constants and geometry, do not absorb in the same range as BO3 units. Bands in the high wavenumber range are rather caused by B-O-(Zn/Ca), O-B-O, B-O-B, and B-O stretching and bending vibrations. The experimental observation of inactive or Raman-active modes in the absorption spectra indicates defects or structural distortions in both compounds. PMID:23973587
NASA Astrophysics Data System (ADS)
Kaindl, Reinhard; Sohr, Gerhard; Huppertz, Hubert
2013-12-01
The two oxoborates ?-ZnB4O7 and ?-CaB4O7 were synthesized and investigated by FTIR- and Raman spectroscopy and ab initio quantum chemical calculations. Maximum and mean deviations between experimentally determined bands and calculated modes ranged between 15-36 cm-1 and 5-7 cm-1, respectively, allowing band assignments to vibrational modes in most cases. The complex network structures with tetrahedral BO4 and planar OB3 groups are mirrored by the spectra and numerous vibrational modes, not assignable by standard borates classification schemes. It was confirmed that OB3 units, despite similar force constants and geometry, do not absorb in the same range as BO3 units. Bands in the high wavenumber range are rather caused by B-O-(Zn/Ca), O-B-O, B-O-B, and B-O stretching and bending vibrations. The experimental observation of inactive or Raman-active modes in the absorption spectra indicates defects or structural distortions in both compounds.
NASA Astrophysics Data System (ADS)
Kidd, Gerald; Mason, Christine R.; Brughera, Andrew; Chiu, Chung-Yiu Peter
2003-08-01
Simultaneous tones that are harmonically related tend to be grouped perceptually to form a unitary auditory image. A partial that is mistuned stands out from the other tones, and harmonic complexes with different fundamental frequencies can readily be perceived as separate auditory objects. These phenomena are evidence for the strong role of harmonicity in perceptual grouping and segregation of sounds. This study measured the discriminability of harmonicity directly. In a two interval, two alternative forced-choice (2I2AFC) paradigm, the listener chose which of two sounds, signal or foil, was composed of tones that more closely matched an exact harmonic relationship. In one experiment, the signal was varied from perfectly harmonic to highly inharmonic by adding frequency perturbation to each component. The foil always had 100% perturbation. Group mean performance decreased from greater than 90% correct for 0% signal perturbation to near chance for 80% signal perturbation. In the second experiment, adding a masker presented simultaneously with the signals and foils disrupted harmonicity. Both monaural and dichotic conditions were tested. Signal level was varied relative to masker level to obtain psychometric functions from which slopes and midpoints were estimated. Dichotic presentation of these audible stimuli improved performance by 3-10 dB, due primarily to a release from ``informational masking'' by the perceptual segregation of the signal from the masker.
NASA Astrophysics Data System (ADS)
Yang, Yue; Gao, Hongwei
2012-04-01
Serotonin (5-hydroxytryptamine, 5-HT) is a monoamine neurotransmitter which plays an important role in treating acute or clinical stress. The comparative performance of different density functional theory (DFT) methods at various basis sets in predicting the molecular structure and vibration spectra of serotonin was reported. The calculation results of different methods including mPW1PW91, HCTH, SVWN, PBEPBE, B3PW91 and B3LYP with various basis sets including LANL2DZ, SDD, LANL2MB, 6-31G, 6-311++G and 6-311+G* were compared with the experimental data. It is remarkable that the SVWN/6-311++G and SVWN/6-311+G* levels afford the best quality to predict the structure of serotonin. The results also indicate that PBEPBE/LANL2DZ level show better performance in the vibration spectra prediction of serotonin than other DFT methods.
NASA Technical Reports Server (NTRS)
Bowman, Joel M.; Gazdy, Bela; Bentley, Joseph A.; Lee, Timothy J.; Dateo, Christopher E.
1993-01-01
A potential energy surface for the HCN/HNC system which is a fit to extensive, high-quality ab initio, coupled-cluster calculations is presented. All HCN and HNC states with energies below the energy of the first delocalized state are reported and characterized. Vibrational transition energies are compared with all available experimental data on HCN and HNC, including high CH-overtone states up to 23,063/cm. A simulation of the (A-tilde)-(X-tilde) stimulated emission pumping (SEP) spectrum is also reported, and the results are compared to experiment. Franck-Condon factors are reported for odd bending states of HCN, with one quantum of vibrational angular momentum, in order to compare with the recent assignment by Jonas et al. (1992), on the basis of axis-switching arguments of a number of previously unassigned states in the SEP spectrum.
Scaling Rules for Vibrational Energy Transport in Globular Proteins.
Buchenberg, Sebastian; Leitner, David M; Stock, Gerhard
2016-01-01
Computational studies of vibrational energy flow in biomolecules have to date mapped out transport pathways on a case-by-case basis. To provide a more general approach, we derive scaling rules for vibrational energy transport in a globular protein, which are identified from extensive nonequilibrium molecular dynamics simulations of vibrational energy flow in the villin headpiece subdomain HP36. We parametrize a master equation based on inter-residue, residue-solvent, and heater-residue energy-transfer rates, which closely reproduces the results of the all-atom simulations. From that fit, two scaling rules emerge, one for energy transport along the protein backbone which relies on a diffusion model and another for energy transport between tertiary contacts, which is based on a harmonic model. Requiring only the calculation of mean and variance of relatively few atomic distances, the approach holds the potential to predict the pathways and time scales of vibrational energy flow in large proteins. PMID:26650387
Structural and vibrational study of maprotiline
NASA Astrophysics Data System (ADS)
Yavuz, A. E.; Haman Bayarı, S.; Kazancı, N.
2009-04-01
Maprotiline ( N-methyl-9,10-ethanoanthracene-9(10H)-propanamine) is a tetra cyclic antidepressant. It is a highly selective inhibitor of norepinephrine reuptake. The solid and solution in CCl 4 and methanol infrared spectra of maprotiline were recorded. The fully optimized equilibrium structure of maprotiline was obtained from DFT calculations by using the B3LYP functional in combination with 6-31G and 6-311G(d,p) basis sets. The results of harmonic and anharmonic frequency calculations on maprotiline were presented. The vibrational spectra were interpreted, with the aid of normal coordinate analysis based on a scaled quantum mechanical (SQM) force field. Vibrational assignment of all the fundamentals was made using the total energy distribution (TED). The possible interaction between maprotiline and neurotransmitter serotonin (5-HT) were investigated.
Mary, Y Sheena; Panicker, C Yohannan; Thiemann, Thies; Al-Azani, Mariam; Al-Saadi, Abdulaziz A; Van Alsenoy, C; Raju, K; War, Javeed Ahmad; Srivastava, S K
2015-12-01
FT-IR and FT-Raman spectra of bis[(E)-anthranyl-9-acrylic]anhydride were recorded and analyzed. The conformational behavior is also investigated. The vibrational wave numbers were calculated using density functional theory (DFT) quantum chemical calculations. The data obtained from wave number calculations are used to assign vibrational bands obtained in Infrared and Raman spectra. Potential energy distribution was done using GAR2PED program. The geometrical parameters are compared with related structures. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using Natural Bonding Orbital (NBO) analysis. The Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) analysis are used to determine the charge transfer within the molecule. Molecular Electrostatic Potential (MEP) was performed by the DFT method. The calculated first hyperpolarizability of the title compound is comparable with the reported values of similar derivatives and is 4.23 times that of the standard nonlinear optical (NLO) material urea and the title compound and its derivatives are an attractive object for future studies of nonlinear optical properties. To evaluate the in silico antitumor activity of the title compound molecular docking studies were carried out against protein Bcl-xL. The (1)H-NMR spectrum is also reported. PMID:26143327
NASA Astrophysics Data System (ADS)
Kruglova, T. V.
2004-01-01
The detailed spectroscope information about highly excited molecules and radicals such us as H+3, H2, HI, H2O, CH2 is needed for a number of applications in the field of laser physics, astrophysics and chemistry. Studies of highly excited molecular vibration-rotation states face several problems connected with slowly convergence or even divergences of perturbation expansions. The physical reason for a perturbation expansion divergence is the large amplitude motion and strong vibration-rotation coupling. In this case one needs to use the special method of series summation. There were a number of papers devoted to this problem: papers 1-10 in the reference list are only example of studies on this topic. The present report is aimed at the application of GET method (Generalized Euler Transformation) to the diatomic molecule. Energy levels of a diatomic molecule is usually represented as Dunham series on rotational J(J+1) and vibrational (V+1/2) quantum numbers (within the perturbation approach). However, perturbation theory is not applicable for highly excited vibration-rotation states because the perturbation expansion in this case becomes divergent. As a consequence one need to use special method for the series summation. The Generalized Euler Transformation (GET) is known to be efficient method for summing of slowly convergent series, it was already used for solving of several quantum problems Refs.13 and 14. In this report the results of Euler transformation of diatomic molecule Dunham series are presented. It is shown that Dunham power series can be represented of functional series that is equivalent to its partial summation. It is also shown that transformed series has the butter convergent properties, than the initial series.
NASA Astrophysics Data System (ADS)
Hussein, M. F. M.; François, S.; Schevenels, M.; Hunt, H. E. M.; Talbot, J. P.; Degrande, G.
2014-12-01
This paper presents an extension of the Pipe-in-Pipe (PiP) model for calculating vibrations from underground railways that allows for the incorporation of a multi-layered half-space geometry. The model is based on the assumption that the tunnel displacement is not influenced by the existence of a free surface or ground layers. The displacement at the tunnel-soil interface is calculated using a model of a tunnel embedded in a full space with soil properties corresponding to the soil in contact with the tunnel. Next, a full space model is used to determine the equivalent loads that produce the same displacements at the tunnel-soil interface. The soil displacements are calculated by multiplying these equivalent loads by Green's functions for a layered half-space. The results and the computation time of the proposed model are compared with those of an alternative coupled finite element-boundary element model that accounts for a tunnel embedded in a multi-layered half-space. While the overall response of the multi-layered half-space is well predicted, spatial shifts in the interference patterns are observed that result from the superposition of direct waves and waves reflected on the free surface and layer interfaces. The proposed model is much faster and can be run on a personal computer with much less use of memory. Therefore, it is a promising design tool to predict vibration from underground tunnels and to assess the performance of vibration countermeasures in an early design stage.
NASA Astrophysics Data System (ADS)
Taleb-Mokhtari, Ilham Naoual; Lazreg, Abbassia; Sekkal-Rahal, Majda; Bestaoui, Noreya
2016-01-01
A structural investigation of the organic molecules is being carried out using vibrational spectroscopy. In this study, normal co-ordinate calculations of anomers of the methyl-D-glucopyranoside and methyl-?-D-xylopyranoside in the crystalline state have been performed using the modified Urey-Bradley-Shimanouchi force field (mUBSFF) combined with an intermolecular potential energy function. The latter includes Van der Waals interactions, electrostatic terms, and explicit hydrogen bond functions. The vibrational spectra of the compounds recorded in the crystalline state, in the 4000-500 cm- 1 spectral region for the IR spectra, and in the 4000-20 cm- 1 spectral range for the Raman spectra are presented. After their careful examination, several differences in the intensities and frequency shifts have been observed. The theoretical spectra have been obtained after a tedious refinement of the force constants. Thus, on the basis of the obtained potential distribution, each observed band in IR and in Raman has been assigned to a vibrational mode. The obtained results are indeed in agreement with those observed experimentally and thus confirm the previous assignments made for the methyl-? and ?-D-glucopyranoside, as well as for the methyl-?-D-xylopyranoside.
Taleb-Mokhtari, Ilham Naoual; Lazreg, Abbassia; Sekkal-Rahal, Majda; Bestaoui, Noreya
2016-01-15
A structural investigation of the organic molecules is being carried out using vibrational spectroscopy. In this study, normal co-ordinate calculations of anomers of the methyl-d-glucopyranoside and methyl-?-d-xylopyranoside in the crystalline state have been performed using the modified Urey-Bradley-Shimanouchi force field (mUBSFF) combined with an intermolecular potential energy function. The latter includes Van der Waals interactions, electrostatic terms, and explicit hydrogen bond functions. The vibrational spectra of the compounds recorded in the crystalline state, in the 4000-500cm(-1) spectral region for the IR spectra, and in the 4000-20cm(-1) spectral range for the Raman spectra are presented. After their careful examination, several differences in the intensities and frequency shifts have been observed. The theoretical spectra have been obtained after a tedious refinement of the force constants. Thus, on the basis of the obtained potential distribution, each observed band in IR and in Raman has been assigned to a vibrational mode. The obtained results are indeed in agreement with those observed experimentally and thus confirm the previous assignments made for the methyl-? and ?-d-glucopyranoside, as well as for the methyl-?-d-xylopyranoside. PMID:26342821
NASA Astrophysics Data System (ADS)
Chain, Fernando E.; Ladetto, María Florencia; Grau, Alfredo; Catalán, César A. N.; Brandán, Silvia Antonia
2016-02-01
In the present work, the structural, topological and vibrational properties of four members of the N-benzylamides series derived from Maca (Lepidium meyenii) whose names are, N-benzylpentadecanamide, N-benzylhexadecanamide, N-benzylheptadecanamide and N-benzyloctadecanamide, were studied combining the FTIR, FT-Raman and 1H and 13C-NMR spectroscopies with density functional theory (DFT) and ONION calculations. Furthermore, the N-benzylacetamide, N-benzylpropilamide and N-benzyl hexanamide derivatives were also studied in order to compare their properties with those computed for the four macamides. These seven N-benzylamides series have a common structure, C8H8NO-R, being R the side chain [-(CH2)n-CH3] with a variable n number of CH2 groups. Here, the atomic charges, molecular electrostatic potentials, stabilization energies, topological properties of those macamides were analyzed as a function of the number of C atoms of the side chain while the frontier orbitals were used to compute the gap energies and some descriptors in order to predict their reactivities and behaviors in function of the longitude of the side chain. Here, the force fields, the complete vibrational assignments and the corresponding force constants were only reported for N-benzylacetamide, N-benzyl hexanamide and N-benzylpentadecanamide due to the high number of vibration normal modes that present the remains macamides.
NASA Astrophysics Data System (ADS)
Han, Peng; Bester, Gabriel
2015-09-01
We perform large-scale ab initio density functional theory calculations to study the lattice strain and the vibrational properties of colloidal semiconductor core-shell nanoclusters with up to one thousand atoms (radii up to 15.6 ). For all the group IV, III-V, and II-VI semiconductors studied, we find that the atom positions of the shell atoms seem unaffected by the core material. In particular, for group-IV core-shell clusters the shell material remains unstrained, while the core adapts to the large lattice mismatch (compressive or tensile strain). For InAs-InP and CdSe-CdS, both the cores and the shells are compressively strained corresponding to pressures up to 20 GPa. We show that this compression, which contributes a large blueshift of the vibrational frequencies, is counterbalanced, to some degree, by the undercoordination effect of the near-surface shell, which contributes a redshift to the vibrational modes. These findings lead to a different interpretation of the frequency shifts of recent Raman experiments, while they confirm the speculated interface nature of the low-frequency shoulder of the high-frequency Raman peak.
Lukose, Jilu; Yohannan Panicker, C; Nayak, Prakash S; Narayana, B; Sarojini, B K; Van Alsenoy, C; Al-Saadi, Abdulaziz A
2015-01-25
The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments of 2-phenyl-N-(pyrazin-2-yl)acetamide have been investigated experimentally and theoretically using Gaussian09 software package. The title compound was optimized by using the HF/6-31G(6D,7F) and B3LYP/6-31G(6D,7F) calculations. The geometrical parameters are in agreement with the XRD data. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. Gauge-including atomic orbital (1)H-NMR chemical shifts calculations were carried out and compared with experimental data. The HOMO and LUMO analysis is used to determine the charge transfer within the molecule. Molecular electrostatic potential was performed by the DFT method. First hyperpolarizability is calculated in order to find its role in non linear optics. From the XRD data, in the crystal, molecules are held together by strong C-H⋯O and N-H⋯O intermolecular interactions. PMID:25124846
NASA Astrophysics Data System (ADS)
Lukose, Jilu; Yohannan Panicker, C.; Nayak, Prakash S.; Narayana, B.; Sarojini, B. K.; Van Alsenoy, C.; Al-Saadi, Abdulaziz A.
2015-01-01
The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments of 2-phenyl-N-(pyrazin-2-yl)acetamide have been investigated experimentally and theoretically using Gaussian09 software package. The title compound was optimized by using the HF/6-31G(6D,7F) and B3LYP/6-31G(6D,7F) calculations. The geometrical parameters are in agreement with the XRD data. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. Gauge-including atomic orbital 1H-NMR chemical shifts calculations were carried out and compared with experimental data. The HOMO and LUMO analysis is used to determine the charge transfer within the molecule. Molecular electrostatic potential was performed by the DFT method. First hyperpolarizability is calculated in order to find its role in non linear optics. From the XRD data, in the crystal, molecules are held together by strong Csbnd H⋯O and Nsbnd H⋯O intermolecular interactions.
NASA Astrophysics Data System (ADS)
Govindarasu, K.; Kavitha, E.
2015-05-01
In this paper, the vibrational wavenumbers of N-(2,4-dinitrophenyl)-L-alanine methyl ester (abbreviated as Dnp-ala-ome) were obtained from ab initio studies based on the density functional theory approach with B3LYP and M06-2X/6-31G(d,p) level of theories. The optimized geometry and structural features of the most potential nonlinear optical crystal Dnp-ala-ome and the vibrational spectral investigations have been thoroughly described with the FT-Raman and FT-IR spectra supported by the DFT computations. FT-IR (4000-400 cm-1) and FT-Raman spectra (3500-50 cm-1) in the solid phase and the UV-Vis spectra that dissolved in ethanol were recorded in the range of 200-800 nm. The Natural population analysis and natural bond orbital (NBO) analysis have also been carried out to analyze the effects of intramolecular charge transfer, intramolecular and hyperconjugative interactions on the geometries. The effects of frontier orbitals, HOMO and LUMO, transition of electron density transfer have also been discussed. The first order hyperpolarizability (?0) and related properties (?, ?0 and ??) of Dnp-ala-ome were calculated. In addition, molecular electrostatic potential (MEP) was investigated using theoretical calculations. The chemical reactivity and thermodynamic properties (heat capacity, entropy and enthalpy) of at different temperature are calculated.
Fan Flutter Computations Using the Harmonic Balance Method
NASA Technical Reports Server (NTRS)
Bakhle, Milind A.; Thomas, Jeffrey P.; Reddy, T.S.R.
2009-01-01
An experimental forward-swept fan encountered flutter at part-speed conditions during wind tunnel testing. A new propulsion aeroelasticity code, based on a computational fluid dynamics (CFD) approach, was used to model the aeroelastic behavior of this fan. This threedimensional code models the unsteady flowfield due to blade vibrations using a harmonic balance method to solve the Navier-Stokes equations. This paper describes the flutter calculations and compares the results to experimental measurements and previous results from a time-accurate propulsion aeroelasticity code.
Relating normal vibrational modes to local vibrational modes: benzene and naphthalene.
Zou, Wenli; Kalescky, Robert; Kraka, Elfi; Cremer, Dieter
2013-07-01
Local vibrational modes can be directly derived from normal vibrational modes using the method of Konkoli and Cremer (Int J Quant Chem 67:29, 1998). This implies the calculation of the harmonic force constant matrix F (q) (expressed in internal coordinates q) from the corresponding Cartesian force constant matrix f (x) with the help of the transformation matrix U = WB ()(BWB ())(-1) (B: Wilson's B-matrix). It is proven that the local vibrational modes are independent of the choice of the matrix W. However, the choice W = M (-1) (M: mass matrix) has numerical advantages with regard to the choice W = I (I: identity matrix), where the latter is frequently used in spectroscopy. The local vibrational modes can be related to the normal vibrational modes in the form of an adiabatic connection scheme (ACS) after rewriting the Wilson equation with the help of the compliance matrix. The ACSs of benzene and naphthalene based on experimental vibrational frequencies are discussed as nontrivial examples. It is demonstrated that the local-mode stretching force constants provide a quantitative measure for the C-H and C-C bond strength. PMID:23263358
The evolution of harmonic Indian musical drums: A mathematical perspective
NASA Astrophysics Data System (ADS)
Gaudet, Samuel; Gauthier, Claude; Léger, Sophie
2006-03-01
We explain using mathematics how harmonic musical drums were discovered by Indian artisans and musicians more than 2000 years ago. To this end, we introduce a harmonic error function which measures the quality of the harmonic relationship and degeneracy of the first modes of vibration of a centrally symmetric loaded membrane. We explain that although the tabla configuration found by the ancient Indians is the most natural one, other configurations exist and some are harmonically superior to the classical one.
Simulation of Payload Vibration Protection by Shape Memory Alloy Parts
NASA Astrophysics Data System (ADS)
Volkov, Aleksandr E.; Evard, Margarita E.; Red'kina, Kristina V.; Vikulenkov, Andrey V.; Makarov, Vyacheslav P.; Moisheev, Aleksandr A.; Markachev, Nikolay A.; Uspenskiy, Evgeniy S.
2014-07-01
A system of vibroisolation under consideration consists of a payload connected to a vibrating housing by plane shape memory alloy (SMA) slotted elements. The calculation of the mechanical behavior of the SMA is based on a microstructural theory. Simulations of harmonic and of impact excitations are carried out. The results have shown that protective properties of this system depend on the SMA state. The maximum reduction of the acceleration amplitude for harmonic excitation is reached when the SMA is in the martensitic (pseudo-plastic) state or in the two-phase state. A variation of temperature allows changing the resonance frequency and thus escaping from the resonance and controlling a mode of vibration.
Analysis on Non-Resonance Standing Waves and Vibration Tracks of Strings
ERIC Educational Resources Information Center
Fang, Tian-Shen
2007-01-01
This paper presents an experimental technique to observe the vibration tracks of string standing waves. From the vibration tracks, we can analyse the vibration directions of harmonic waves. For the harmonic wave vibrations of strings, when the driving frequency f[subscript s] = Nf[subscript n] (N = 1, 2, 3, 4,...), both resonance and non-resonance
Analysis on Non-Resonance Standing Waves and Vibration Tracks of Strings
ERIC Educational Resources Information Center
Fang, Tian-Shen
2007-01-01
This paper presents an experimental technique to observe the vibration tracks of string standing waves. From the vibration tracks, we can analyse the vibration directions of harmonic waves. For the harmonic wave vibrations of strings, when the driving frequency f[subscript s] = Nf[subscript n] (N = 1, 2, 3, 4,...), both resonance and non-resonance…
Yu, Hua-Gen
2004-02-01
Two quantum mechanical Hamiltonians have been derived in orthogonal polyspherical coordinates, which can be formed by Jacobi and/or Radau vectors etc., for the study of the vibrational spectra of six-atom molecules. The Hamiltonians are expressed in an explicit Hermitian form in the spatial representation. Their matrix representations are described in both full discrete variable representation (DVR) and mixed DVR/nondirect product finite basis representation (FBR) bases. The two-layer Lanczos iteration algorithm [H.-G. Yu, J. Chem. Phys. 117, 8190 (2002)] is employed to solve the eigenvalue problem of the system. A strategy regarding how to carry out the Hamiltonian-vector products for a high-dimensional problem is discussed. By exploiting the inversion symmetry of molecules, a unitary sequential 1D matrix-vector multiplication algorithm is proposed to perform the action of the Hamiltonian on the wavefunction in a symmetrically adapted DVR or FBR basis in the azimuthal angular variables. An application to the vibrational energy levels of the molecular hydrogen trimer (H2)3 in full dimension (12D) is presented. Results show that the rigid-H2 approximation can underestimate the binding energy of the trimer by 27%. Finally, it is demonstrated that the two-layer Lanczos algorithm is also capable of computing the eigenvectors of the system with minor effort. PMID:15268366
Morzyk-Ociepa, Barbara; Dysz, Karolina; Turowska-Tyrk, Ilona; Michalska, Danuta
2015-02-01
3-Chloro-7-azaindole (3Cl7AI) is the carrier ligand in a new anticancer platinum(II) agent cis-[PtCl2(3Cl7AI)2]. In this work 3Cl7AI has been studied by a single crystal X-ray diffraction, infrared and Raman spectroscopy and density functional calculations. The compound crystallizes in the monoclinic system, space group P21/n, with a=12.3438(3), b=3.85964(11), c=14.4698(4), ?=100.739(2), V=677.31(3)(3) and Z=4. In the crystal, a pair of 3Cl7AI molecules forms a centrosymmetric dimer linked by the moderately strong dual N-H?N hydrogen bonds. The nitrogen atom in the pyrrole ring acts as the proton donor, while the nitrogen atom in the pyridine ring is the proton acceptor. The FT-IR and FT-Raman spectra (3500-60 cm(-1)) have been recorded. The theoretical studies on the molecular structures and vibrational spectra of the monomeric and dimeric forms of 3Cl7AI and its N-deuterated derivative were performed using the B3LYP method with 6-311++G(d,p) basis set. The theoretically predicted Raman spectrum for the dimer shows very good agreement with experiment. Detailed vibrational assignments for the two isotopomers have been made on the basis of the calculated potential energy distributions (PEDs). The dual N-H?N hydrogen bonds in 3Cl7AI dimer are characterized by a very broad and complicated structure of the absorption band between 3300 and 2500 cm(-1), which is caused by multiple Fermi resonances between the N-H stretching vibration and various combinations bands. PMID:25315872
NASA Astrophysics Data System (ADS)
Morzyk-Ociepa, Barbara; Dysz, Karolina; Turowska-Tyrk, Ilona; Michalska, Danuta
2015-02-01
3-Chloro-7-azaindole (3Cl7AI) is the carrier ligand in a new anticancer platinum(II) agent cis-[PtCl2(3Cl7AI)2]. In this work 3Cl7AI has been studied by a single crystal X-ray diffraction, infrared and Raman spectroscopy and density functional calculations. The compound crystallizes in the monoclinic system, space group P21/n, with a = 12.3438(3), b = 3.85964(11), c = 14.4698(4) , ? = 100.739(2), V = 677.31(3) 3 and Z = 4. In the crystal, a pair of 3Cl7AI molecules forms a centrosymmetric dimer linked by the moderately strong dual N-H⋯N hydrogen bonds. The nitrogen atom in the pyrrole ring acts as the proton donor, while the nitrogen atom in the pyridine ring is the proton acceptor. The FT-IR and FT-Raman spectra (3500-60 cm-1) have been recorded. The theoretical studies on the molecular structures and vibrational spectra of the monomeric and dimeric forms of 3Cl7AI and its N-deuterated derivative were performed using the B3LYP method with 6-311++G(d,p) basis set. The theoretically predicted Raman spectrum for the dimer shows very good agreement with experiment. Detailed vibrational assignments for the two isotopomers have been made on the basis of the calculated potential energy distributions (PEDs). The dual N-H⋯N hydrogen bonds in 3Cl7AI dimer are characterized by a very broad and complicated structure of the absorption band between 3300 and 2500 cm-1, which is caused by multiple Fermi resonances between the N-H stretching vibration and various combinations bands.
NASA Technical Reports Server (NTRS)
Bielawa, R. L.
1984-01-01
The mathematical development for the expanded capabilities of the G400 rotor aeroelastic analysis was examined. The G400PA expanded analysis simulates the dynamics of all conventional rotors, blade pendulum vibration absorbers, and the higher harmonic excitations resulting from prescribed vibratory hub motions and higher harmonic blade pitch control. The methodology for modeling the unsteady stalled airloads of two dimensional airfoils is discussed. Formulations for calculating the rotor impedance matrix appropriate to the higher harmonic blade excitations are outlined. This impedance matrix, and the associated vibratory hub loads, are the rotor dynamic characteristic elements for use in the simplified coupled rotor/fuselage vibration analysis (SIMVIB). Updates to the development of the original G400 theory, program documentation, user instructions and information are presented.
NASA Astrophysics Data System (ADS)
Morzyk-Ociepa, Barbara; Dysz, Karolina; Turowska-Tyrk, Ilona; Michalska, Danuta
2015-12-01
5-Bromo-7-azaindole (5Br7AI) may act as the carrier ligand for platinum(II), in new anticancer agent, cis-[PtCl2(5Br7AI)2]. The crystal and molecular structure of the title molecule has been reinvestigated by a single crystal X-ray diffraction. The FT-IR and FT-Raman spectra of (5Br7AI) and its N-deuterated derivative have been recorded. The molecular structures of monomer and dimer, natural charges on atoms and theoretical vibrational spectra have been studied by density functional B3LYP method using 6-311++G(d,p) basis set. The results have shown that in the crystal, a pair of 5Br7AI molecules forms a centrosymmetric dimer linked by the moderately strong, dual and nearly linear N-H???N hydrogen bonds between the pyrrole and pyridine rings. The optimized geometry of the (5Br7AI)2 dimer and the calculated spectra show very good agreement with the experiment. Detailed vibrational assignments for all the species have been made on the basis of the calculated potential energy distributions (PEDs). It is concluded that a complicated spectral features of the NH (ND) stretching absorption bands are due to multiple Fermi resonances, and they are characteristic for the doubly hydrogen bonded N-H???N dimers of 7-azaindole and its halogeno derivatives.
NASA Astrophysics Data System (ADS)
Kouach-Alix, I.; Vergoten, G.
1994-07-01
Combining the modified UreyBradleyShimanouchi intramolecular potential energy function with an appropriate intermolecular energy function, normal coordinate calculations have been performed for N-acetyl-?- D-glucosamine in the crystalline state. The infrared spectra in the mid range (4000-500 cm -1) and the Raman spectra in 3500-20 cm -1 range were recorded. The overall agreement between the observed and calculated frequencies led to an average error of the order of 3.5 cm -1. The computed potential energy distribution was found to be compatible with previous assignments of D-glucose and D-galactose for the pyranose ring and for N-methylacetamide for the acetamido group. The set of force constants used for N-acetyl-?- D-glucosamine was approximately the same as that obtained for the glucose and N-methylacetamide respectively for the pyranose ring and the acetamido group, a difference existing only for the atoms involved in the anomeric and hydroxy groups.
A finite element method for nonlinear forced vibrations of beams
NASA Technical Reports Server (NTRS)
Mei, C.; Decha-Umphai, K.
1984-01-01
Techniques for defining a finite element model (FEM) for analysis of nonlinear vibrations in beam structures subjected to harmonic excitation are presented. The resulting model covers longitudinal deformation and inertial effects. The nonlinear oscillations of a beam element under forced excitation are modeled by a harmonic force matrix based on first order approximations of the Jacobian elliptic forcing function. Harmonic force and nonlinear stiffness matrices are derived and the nonlinear forced responses of beams are calculated under various boundary conditions. The results of FEM computations for simply-supported and clamped beams show that midplane stretching caused by large deflections increases the nonlinearity. Axially-restrained beams experience only hardening nonlinearity, while axially-free beams have reduced nonlinearity in deformation and inertia and an increase in linearity due to large deflection.
Vibrational Spectral Studies and Ab initio Computations of a Nonlinear Food Dye Carmoisine
NASA Astrophysics Data System (ADS)
Snehalatha, M.; Ravikumar, C.; Sekar, N.; Jayakumar, V. S.; Joe, I. Hubert
2008-11-01
FT-IR and Raman techniques were employed for the vibrational characterization of the food dye Carmoisine (E122). The equilibrium geometry, various bonding features, and harmonic vibrational wavenumbers have been investigated with the help of density functional theory (DFT) calculations. The first hyperpolarizability of the molecule is calculated. A good correlation was found between the computed and experimental wavenumbers. Azo stretching wavenumbers have been lowered due to conjugation and ?-electron delocalization. The optimized structure indicates intramolecular C-H O=S hydrogen bonding in the molecule. Intramolecular charge transfer (ICT) responsible for the optical nonlinearity of the dye molecule has been discussed theoretically and experimentally.
NASA Astrophysics Data System (ADS)
Mishra, Alok; Srivastava, Sunil Kumar; Swati, D.
2013-09-01
The structure-activity relationship of the anticoagulant drug warfarin were studied by studying two enantiomeric forms (S-form and R-form) of warfarin and its protonated as well as deprotonated structures in aqueous media using density functional theory (DFT). Theoretically computed Raman and IR spectra of all the computed structures were compared and their specific vibrational spectroscopic signatures were discussed. The percentage contributions of individual normal modes of warfarin, which provides direct evidence of the different molecular activity due to change in relative atomic position of atoms in molecule, were investigated through potential energy distribution (PED). The optimized energy and molecular electrostatic potential (MEP) maps show that the S-form of the drug molecules warfarin is energetically more stable than R-form and provides higher docking opportunity for the molecular binding with the receptors in the bio-systems.
Mishra, Alok; Srivastava, Sunil Kumar; Swati, D
2013-09-01
The structure-activity relationship of the anticoagulant drug warfarin were studied by studying two enantiomeric forms (S-form and R-form) of warfarin and its protonated as well as deprotonated structures in aqueous media using density functional theory (DFT). Theoretically computed Raman and IR spectra of all the computed structures were compared and their specific vibrational spectroscopic signatures were discussed. The percentage contributions of individual normal modes of warfarin, which provides direct evidence of the different molecular activity due to change in relative atomic position of atoms in molecule, were investigated through potential energy distribution (PED). The optimized energy and molecular electrostatic potential (MEP) maps show that the S-form of the drug molecules warfarin is energetically more stable than R-form and provides higher docking opportunity for the molecular binding with the receptors in the bio-systems. PMID:23747386
Vibrational spectra of tris(acetylacetonato)chromium(III)
NASA Astrophysics Data System (ADS)
Dolati, Fatemeh; Vakili, Mohammad; Ebrahimi, Ali; Tayyari, Sayyed Faramarz
2015-11-01
The molecular structure and vibrational spectra of tris(acetylacetonato)chromium(III), Cr (AA)3, its mono-deuterated, Cr (DAA)3, and per-deuterated analogous, Cr(D7AA)3, were investigated using density functional theory (DFT) calculations. The geometry of the titled compound was fully optimized at the B3LYP level using 6-311+G* and 6-31G** basis sets. The harmonic vibrational frequencies were obtained at the B3LYP/6-311+G** level. Raman scattering activities were calculated at the B3LYP/6-31G** level. The calculated frequencies are compared with the experimental IR and Raman spectra. All of the measured IR and Raman bands were interpreted in terms of the calculated vibrational modes and isotopic frequency shifts. The scaled theoretical frequencies and the structural parameters are in excellent agreement with the experimental data. Analysis of the vibrational spectra indicates a strong coupling between the chelated ring modes. Several bands at 933, 680, 611, 594, 495, 250, 224, and 179cm-1 are found to be engaged in Cr-O vibrational movements. The IR bands at 611 and 594cm-1 are attributed to the asymmetric Cr-O stretching and the very strong Raman band at 460cm-1 is assigned to the totally symmetric Cr-O stretching mode (a1 species).
Technology Transfer Automated Retrieval System (TEKTRAN)
The structures and energies of glucose and glucose monohydrates have been calculated at the B3LYP/6-311++G** level of theory. Both the alpha and beta anomers were studied, with all possible combinations of hydroxymethyl rotamer (gg, gt, or tg) and hydroxyl orientation (clockwise or counter-clockwis...
Electron-vibration energy exchange models in nitrogen plasma flows
NASA Astrophysics Data System (ADS)
Bourdon, A.; Vervisch, P.
1997-04-01
This work presents an examination of the validity of the simple linear Landau-Teller-type model proposed by Lee for the electron-vibration energy exchange term in nitrogen [in Thermal Design of Aeroassisted Orbital Transfer Vehicles, edited by H. F. Nelson (AIAA, New York, 1985), Vol. 96, p. 3; in Thermophysical Aspects of Re-entry Flows, edited by J. N. Moss and C. D. Scott (AIAA, New York, 1986), Vol. 103, p. 197]. Plasma flow conditions encountered in high enthalpy wind tunnels are considered. The time-dependent relaxation of the vibrational energy of nitrogen due to electron inelastic collisions is calculated. The influence of the anharmonicity of the molecule and of the initial vibrational temperature Tv is studied. With a harmonic oscillator approximation, it is found that a linear Landau-Teller-type model is accurate to describe the vibrational energy relaxation rate for electron temperatures Te in the range 3000 K<=Te<=20 000 K. When Tv
Tasinato, Nicola; Regini, Giorgia; Stoppa, Paolo; Pietropolli Charmet, Andrea; Gambi, Alberto
2012-06-01
Difluoromethane (CH(2)F(2), HFC-32) is a molecule used in refrigerant mixtures as a replacement of the more environmentally hazardous, ozone depleting, chlorofluorocarbons. On the other hand, presenting strong vibration-rotation bands in the 9 ?m atmospheric window, it is a greenhouse gas which contributes to global warming. In the present work, the vibrational and ro-vibrational properties of CH(2)F(2), providing basic data for its atmospheric modeling, are studied in detail by coupling medium resolution Fourier transform infrared spectroscopy to high-level electronic structure ab initio calculations. Experimentally a full quantum assignment and accurate integrated absorption cross sections are obtained up to 5000 cm(-1). Ab initio calculations are carried out by using CCSD(T) theory and large basis sets of either the correlation consistent or atomic natural orbital hierarchies. By using vibrational perturbation theory to second order a complete set of vibrational and ro-vibrational parameters is derived from the ab initio quartic anharmonic force fields, which well compares with the spectroscopic constants retrieved experimentally. An excellent agreement between theory and experiment is achieved for vibrational energy levels and integrated absorption cross sections: transition frequencies up to four quanta of vibrational excitation are reproduced with a root mean square deviation (RMSD) of 7 cm(-1) while intensities are predicted within few km mol(-1) from the experiment. Basis set performances and core correlation effects are discussed throughout the paper. Particular attention is focused in the understanding of the anharmonic couplings which rule the vibrational dynamics of the |?(1)>, |2?(8)>, |2?(2)> three levels interacting system. The reliability of the potential energy and dipole moment surfaces in reproducing the vibrational eigenvalues and intensities as well as in modeling the vibrational and ro-vibrational mixings over the whole 400-5000 cm(-1) region is also demonstrated by spectacular spectral simulations carried out by using the ro-vibrational Hamiltonian constants, and the relevant coupling terms, obtained from the perturbation treatment of the ab initio anharmonic force field. The present results suggest CH(2)F(2) as a prototype molecule to test ab initio calculations and theoretical models. PMID:22697538
Vibrational spectra of ?-bromo and ?-chloro derivatives of tris(acetylacetonato)chromium(III)
NASA Astrophysics Data System (ADS)
Dolati, Fatemeh; Tayyari, Sayyed Faramarz; Vakili, Mohammad; Ebrahimi, Ali
2016-01-01
The molecular structure and vibrational spectra of ?-chloro and ?-bromo derivatives of tris(acetylacetonato)chromium(III), Cr(ClAA)3 and Cr(BrAA)3, were investigated using the density functional theory (DFT) calculations. The geometrical parameters and harmonic vibrational wavenumbers of the titled compounds were obtained at the B3LYP level, using 6-311+G(d) and 6-31G** basis sets. The calculated vibrational wavenumbers were compared with the corresponding experimental results and those of tris(acetylacetonato)chromium(III), Cr(AA)3. The effects of chlorine and bromine substitutions at the ?-position on the vibrational spectra and geometry of Cr(AA)3 were studied. The ?-halo substitution effects were also investigated using the natural bond orbital, NBO, analysis.
Luo, Ye Sorella, Sandro; Zen, Andrea
2014-11-21
We present a systematic study of a recently developed ab initio simulation scheme based on molecular dynamics and quantum Monte Carlo. In this approach, a damped Langevin molecular dynamics is employed by using a statistical evaluation of the forces acting on each atom by means of quantum Monte Carlo. This allows the use of an highly correlated wave function parametrized by several variational parameters and describing quite accurately the Born-Oppenheimer energy surface, as long as these parameters are determined at the minimum energy condition. However, in a statistical method both the minimization method and the evaluation of the atomic forces are affected by the statistical noise. In this work, we study systematically the accuracy and reliability of this scheme by targeting the vibrational frequencies of simple molecules such as the water monomer, hydrogen sulfide, sulfur dioxide, ammonia, and phosphine. We show that all sources of systematic errors can be controlled and reliable frequencies can be obtained with a reasonable computational effort. This work provides convincing evidence that this molecular dynamics scheme can be safely applied also to realistic systems containing several atoms.
Luo, Ye; Zen, Andrea; Sorella, Sandro
2014-11-21
We present a systematic study of a recently developed ab initio simulation scheme based on molecular dynamics and quantum Monte Carlo. In this approach, a damped Langevin molecular dynamics is employed by using a statistical evaluation of the forces acting on each atom by means of quantum Monte Carlo. This allows the use of an highly correlated wave function parametrized by several variational parameters and describing quite accurately the Born-Oppenheimer energy surface, as long as these parameters are determined at the minimum energy condition. However, in a statistical method both the minimization method and the evaluation of the atomic forces are affected by the statistical noise. In this work, we study systematically the accuracy and reliability of this scheme by targeting the vibrational frequencies of simple molecules such as the water monomer, hydrogen sulfide, sulfur dioxide, ammonia, and phosphine. We show that all sources of systematic errors can be controlled and reliable frequencies can be obtained with a reasonable computational effort. This work provides convincing evidence that this molecular dynamics scheme can be safely applied also to realistic systems containing several atoms. PMID:25416879
Ritchie, Andrew W; Webb, Lauren J
2015-11-01
Biological function emerges in large part from the interactions of biomacromolecules in the complex and dynamic environment of the living cell. For this reason, macromolecular interactions in biological systems are now a major focus of interest throughout the biochemical and biophysical communities. The affinity and specificity of macromolecular interactions are the result of both structural and electrostatic factors. Significant advances have been made in characterizing structural features of stable protein-protein interfaces through the techniques of modern structural biology, but much less is understood about how electrostatic factors promote and stabilize specific functional macromolecular interactions over all possible choices presented to a given molecule in a crowded environment. In this Feature Article, we describe how vibrational Stark effect (VSE) spectroscopy is being applied to measure electrostatic fields at protein-protein interfaces, focusing on measurements of guanosine triphosphate (GTP)-binding proteins of the Ras superfamily binding with structurally related but functionally distinct downstream effector proteins. In VSE spectroscopy, spectral shifts of a probe oscillator's energy are related directly to that probe's local electrostatic environment. By performing this experiment repeatedly throughout a protein-protein interface, an experimental map of measured electrostatic fields generated at that interface is determined. These data can be used to rationalize selective binding of similarly structured proteins in both in vitro and in vivo environments. Furthermore, these data can be used to compare to computational predictions of electrostatic fields to explore the level of simulation detail that is necessary to accurately predict our experimental findings. PMID:26375183
Guo, Y.; Keller, J.; Parker, R. G.
2012-06-01
The dynamics of wind turbine planetary gears with gravity effects are investigated using an extended harmonic balance method that extends established harmonic balance formulations to include simultaneous internal and external excitations. The extended harmonic balance method with arc-length continuation and Floquet theory is applied to a lumped-parameter planetary gear model including gravity, fluctuating mesh stiffness, bearing clearance, and nonlinear tooth contact to obtain the planetary gear dynamic response. The calculated responses compare well with time domain integrated mathematical models and experimental results. Gravity is a fundamental vibration source in wind turbine planetary gears and plays an important role in system dynamics, causing hardening effects induced by tooth wedging and bearing-raceway contacts. Bearing clearance significantly reduces the lowest resonant frequencies of translational modes. Gravity and bearing clearance together lowers the speed at which tooth wedging occurs lower than the resonant frequency.
Neff, Michael; Rauhut, Guntram
2014-02-01
Multidimensional potential energy surfaces obtained from explicitly correlated coupled-cluster calculations and further corrections for high-order correlation contributions, scalar relativistic effects and core-correlation energy contributions were generated in a fully automated fashion for the double-minimum benchmark systems OH3(+) and NH3. The black-box generation of the potentials is based on normal coordinates, which were used in the underlying multimode expansions of the potentials and the ?-tensor within the Watson operator. Normal coordinates are not the optimal choice for describing double-minimum potentials and the question remains if they can be used for accurate calculations at all. However, their unique definition is an appealing feature, which removes remaining errors in truncated potential expansions arising from different choices of curvilinear coordinate systems. Fully automated calculations are presented, which demonstrate, that the proposed scheme allows for the determination of energy levels and tunneling splittings as a routine application. PMID:23548204
Harmonic generation at high intensities
Schafer, K.J.; Krause, J.L.; Kulander, K.C.
1993-06-01
Atomic electrons subject to intense laser fields can absorb many photons, leading either to multiphoton ionization or the emission of a single, energetic photon which can be a high multiple of the laser frequency. The latter process, high-order harmonic generation, has been observed experimentally using a range of laser wavelengths and intensities over the past several years. Harmonic generation spectra have a generic form: a steep decline for the low order harmonics, followed by a plateau extending to high harmonic order, and finally an abrupt cutoff beyond which no harmonics are discernible. During the plateau the harmonic production is a very weak function of the process order. Harmonic generation is a promising source of coherent, tunable radiation in the XUV to soft X-ray range which could have a variety of scientific and possibly technological applications. Its conversion from an interesting multiphoton phenomenon to a useful laboratory radiation source requires a complete understanding of both its microscopic and macroscopic aspects. We present some recent results on the response of single atoms at intensities relevant to the short pulse experiments. The calculations employ time-dependent methods, which we briefly review in the next section. Following that we discuss the behavior of the harmonics as a function of laser intensity. Two features are notable: the slow scaling of the harmonic intensities with laser intensity, and the rapid variation in the phase of the individual harmonics with respect to harmonic order. We then give a simple empirical formula that predicts the extent of the plateau for a given ionization potential, wavelength and intensity.
Bennett, Charles L.
2009-10-20
A high efficiency harmonic engine based on a resonantly reciprocating piston expander that extracts work from heat and pressurizes working fluid in a reciprocating piston compressor. The engine preferably includes harmonic oscillator valves capable of oscillating at a resonant frequency for controlling the flow of working fluid into and out of the expander, and also preferably includes a shunt line connecting an expansion chamber of the expander to a buffer chamber of the expander for minimizing pressure variations in the fluidic circuit of the engine. The engine is especially designed to operate with very high temperature input to the expander and very low temperature input to the compressor, to produce very high thermal conversion efficiency.
NASA Astrophysics Data System (ADS)
Schrder, Markus; Meyer, Hans-Dieter
2014-07-01
We report energies and tunneling splittings of vibrational excited states of malonaldehyde which have been obtained using full dimensional quantum mechanical calculations. To this end we employed the multi configuration time-dependent Hartree method. The results have been obtained using a recently published potential energy surface [Y. Wang, B. J. Braams, J. M. Bowman, S. Carter, and D. P. Tew, J. Chem. Phys. 128, 224314 (2008)] which has been brought into a suitable form by a modified version of the n-mode representation which was used with two different arrangements of coordinates. The relevant terms of the expansion have been identified with a Metropolis algorithm and a diffusion Monte-Carlo technique, respectively.
Schrder, Markus Meyer, Hans-Dieter
2014-07-21
We report energies and tunneling splittings of vibrational excited states of malonaldehyde which have been obtained using full dimensional quantum mechanical calculations. To this end we employed the multi configuration time-dependent Hartree method. The results have been obtained using a recently published potential energy surface [Y. Wang, B. J. Braams, J. M. Bowman, S. Carter, and D. P. Tew, J. Chem. Phys. 128, 224314 (2008)] which has been brought into a suitable form by a modified version of the n-mode representation which was used with two different arrangements of coordinates. The relevant terms of the expansion have been identified with a Metropolis algorithm and a diffusion Monte-Carlo technique, respectively.
Ab initio structural and vibrational investigation of sulfuric acid monohydrate.
Partanen, Lauri; Hänninen, Vesa; Halonen, Lauri
2012-03-22
We employ ab initio methods to find stable geometries and to calculate potential energy surfaces and vibrational wavenumbers for sulfuric acid monohydrate. Geometry optimizations are carried out with the explicitly correlated coupled-cluster approach that includes single, double, and perturbative triple excitations (CCSD(T)-F12a) with a valence double-ζ basis set (VDZ-F12). Four different stable geometries are found, and the two lowest are within 0.41 kJ mol(-1) (or 34 cm(-1)) of each other. Vibrational harmonic wavenumbers are calculated at both the density-fitted local spin component scaled second-order Møller-Plesset perturbation theory (DF-SCS-LMP2) with the aug-cc-pV(T+d)Z basis set and the CCSD-F12/VDZ-F12 level. Water O-H stretching vibrations and two highly anharmonic large-amplitude motions connecting the three lowest potential energy minima are considered by limiting the dimensionality of the corresponding potential energy surfaces to small two- or three-dimensional subspaces that contain only strongly coupled vibrational degrees of freedom. In these anharmonic domains, the vibrational problem is solved variationally using potential energy surfaces calculated at the CCSD(T)-F12a/VDZ-F12 level. PMID:22260481
Vibrational overtone stretching transitions in sarin
NASA Astrophysics Data System (ADS)
Petryk, Michael W. P.
2006-10-01
The CH stretching overtone transitions of the nerve agent sarin (O-isopropyl methylphosphonofluoridate) are of interest to the standoff detection of chemical warfare agents, as many of these transitions occur near regions where small, efficient, portable diode lasers (originally developed for use in the telecommunications industry) operate. However, the interpretation of experimental vibrational overtone spectra is often difficult, and the computational simulation of overtone transitions in a molecule is challenging. Presented herein are the simulated CH overtone stretching transitions in sarin. Spectral regions are simulated from overtone transition energies and intensities, both of which are calculated within the harmonically coupled anharmonic oscillator (HCAO) model. Data for HCAO calculations are obtained from ab initio calculations, without any recourse to experimental data.
Anand, S; Sundararajan, R S; Ramachandraraja, C; Ramalingam, S; Durga, R
2015-03-01
In the present research work, the FT-IR, FT-Raman spectra of the Bis(thiourea) Nickel chloride (BTNC) were recorded and analyzed. The observed fundamental frequencies in finger print and functional group regions were assigned according to their uniqueness region. The computational calculations were carried out by HF and DFT (B3LYP and B3PW91) methods with 6-31++G(d,p) and 6-311++G(d,p) basis sets and the corresponding results were tabulated. The present organo-metallic compound was made up of covalent and coordination covalent bonds. The modified vibrational pattern of the complex molecule associated with ligand group was analyzed. Furthermore, the (13)C NMR and (1)H NMR spectral data were calculated by using the gauge independent atomic orbital (GIAO) method with B3LYP/6-311++G(d,p) basis set and their spectra were simulated and the chemical shifts linked to TMS were compared. A investigation on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies were carried out. The kubo gap of the present compound was calculated related to HOMO and LUMO energies which confirm the occurring of charge transformation between the base and ligand. Besides frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) was performed. The NLO properties related to Polarizability and hyperpolarizability based on the finite-field approach were also discussed. PMID:25498815
Shaltout, I; Mohamed, Tarek A
2007-06-01
Chozen system of tellurite glasses doped with rare earth oxides (95% alpha-TeO(2)+5% Sm2O3) was prepared by melt quenching. Consequently, the Raman spectrum (150-1250 cm(-1)) of the modified tellurite have been recorded. As a continuation to our normal coordinate analysis, force constants and quantum mechanical (QM) calculations for tbp TeO4(4-) (triagonal bipyramid, C(2v)) and TeO(3+1); Te2O7(6-) (bridged tetrahedral), we have carried out ab initio frequency calculations for tpy TeO3(2-) (triagonal pyramidal, C(3v) and C(s)) and tp TeO3(2-) (triagonal planar, D(3h)) ions. The quantum mechanical calculations at the levels of RHF, B3LYP and MP2 allow confident vibrational assignments and structural identification in the binary oxide glass (95% alpha-TeO2 +5% Sm2O3). The dominant three-dimensional network structures in the modified glass are triagonal pyramidal TeO3 with minor features of short range distorted tbp TeO4 and bridged tetrahedral unit of TeO(3+1), leading to a structure of infinite chain. Therefore, alpha-TeO2/Sm2O3 (95/5%) glass experience structural changes from TeO4 (tbp); Te2O7 (TeO(3+1))-->TeO3 (tpy). PMID:16982208
NASA Astrophysics Data System (ADS)
Boopalachandran, Praveenkumar; Sheu, Hong-Li; Laane, Jaan
2012-09-01
The infrared and Raman spectra of 2-chloropyridine, 3-chloropyridine, 2-bromopyridine, and 3-bromopyridine have been recorded and assigned. Density functional theory calculations (B3LYP with 6-311++G(d,p) basis set) produce excellent agreement with the experimental values. Ab initio calculations (MP2 with the cc-pVTZ basis set) were utilized to compute the molecular structures, which were compared to those of pyridine and the corresponding fluoropyridines. All of the 2-halopyridines show a shortening of the N-C(2) bond resulting from the halogen substitution on the C(2) carbon atom. All of the other ring bond distances for the 2-halopyridines and 3-halopyridines are little different from pyridine itself.
Gavezzotti, A
2005-09-01
Quantum chemical calculations including electron correlation and calculations with the density sums (Pixel) method have been performed on a variety of molecular dimers representing some frequently observed recognition modes in molecular condensed phases. Notwithstanding some individual fluctuations when different computational methods are used, there is a general agreement for the relative orders of magnitude. The results have been collected in a table that ranks the interaction energies and amplitudes of the energy wells for the recognition between molecular fragments, providing a quantitative guideline to assess the relative importance of hydrogen bonding, aromatic ring stacking, antiparallel arrangements of polar moieties, weak Coulombic C-HX interactions, and dispersive interactions between nonpolar groups. Since the Pixel method naturally allows for a separation between Coulombic, dispersion, polarization, and repulsion energy contributions, their relative importance can be analyzed with respect to the chemical constitution of the interacting partners. The relevance of these results to the current ideas and methods of "crystal engineering" is discussed. PMID:26641899
Vibrational Calculations of Higher-Order Weakly Bound Complexes: The He3,4I2 Cases.
Valds, lvaro; Prosmiti, Rita
2015-12-24
The structure and relative stability of higher-order He3,4I2 clusters are investigated by carrying out full-dimensional quantum calculations within the multiconfiguration time-dependent Hartree framework. The full interaction between the I2 molecule and the He atoms is based on analytical three-body ab initio He-I2 potentials obtained from high level ab initio calculations plus the He-He interaction. The low-lying minima on the potential surfaces are found to be very close in energy with the He atoms in a ring encircling the dopant for the global minimum structure, while for the local minima one or two of the He atoms prefer the linear arrangements along the I2-axis. Such classical description on the basis of the potential energy landscape is corrected by including anharmonic quantum effects, present in highly floppy systems, by carrying out full dimensional quantum calculations. The potential energy operator was constructed by natural potential fits, while a mode combination scheme was employed to optimize the computational cost of the improved relaxation calculations. The obtained results predict the relative stability of the He3,4I2 isomers at zero temperature and provide benchmark data on binding energies and structural properties of these van der Waals systems. The (2,1) and (2,2), involving two He atoms in the T-shape and one or two He atoms in the linear configurations, respectively, are found to be the most stable isomers, although extremely close in energy with the (3,0) and (4,0) ones as predicted by classical optimizations. Comparison with experimental data on similar systems at low temperatures is also discussed. This analysis indicates once more the importance of quantum delocalization and the need of accurate quantum-mechanical treatments to characterize such doped helium nanosystems. PMID:26634405
NASA Astrophysics Data System (ADS)
Barczy?ski, P.; Ratajczak-Sitarz, M.; Katrusiak, A.; Szafran, M.
2010-07-01
The crystals of 1-methyl-6-oxyquinolinium betaine dihydrate, 6QB2H 2O, are triclinic, space group P1. The oxygen atom of 6QB exhibits an extremely rare capability of accepting four hydrogen bonds. It is engaged in four hydrogen bonds to water molecules of the 2.823, 2.825, 2.833 and 2.849 ; each water molecule interacts with two neighbouring 6QB molecules linking them into infinite sheets. Differences in geometrical parameters between the X-ray and calculated molecules reflect changes in their structures between zwitterion and quinonoid forms. The probable assignments of the experimental FTIR solid spectrum have been made on the basis of B3LYP/6-311G(d,p) calculated frequencies in vacuum. Both 1H and 13C chemical shifts are solvent dependent. Linear correlations between the experimental 1H and 13C NMR chemical shifts of 6QB2H 2O in solutions and the GIAO/B3LYP/6-311G(d,p) calculated magnetic isotropic shielding tensors ( ?cal) using the screening solvation model, ?exp = a + b?cal, are reported.
Anharmonic vibrations of the dicarbon antisite defect in 4H-SiC
Yan, F.; Devaty, R. P.; Choyke, W. J.; Gali, A.; Kimoto, T.; Ohshima, T.; Pensl, G.
2012-03-26
Dicarbon antisite defects were created by either electron irradiation or ion implantation into 4H-SiC. The no-phonon lines from the dicarbon antisite defect center were observed with their phonon replicas. The stretch frequencies of the defect were observed up to the fifth harmonic. The Morse potential model accounts for the anharmonicity quite well and gives a very good prediction of the vibration energies up to the fifth harmonic with an error of less than 1%. First principles calculations show that the model of a dicarbon antisite defect along with its four nearest neighboring carbon atoms can explain the observed anharmonicity.
Vibrational coupled cluster theory
NASA Astrophysics Data System (ADS)
Christiansen, Ove
2004-02-01
The theory and first implementation of a vibrational coupled cluster (VCC) method for calculations of the vibrational structure of molecules is presented. Different methods for introducing approximate VCC methods are discussed including truncation according to a maximum number of simultaneous mode excitations as well as an interaction space order concept is introduced. The theory is tested on calculation of anharmonic frequencies for a three-mode model system and a formaldehyde quartic force field. The VCC method is compared to vibrational self-consistent-field, vibrational Mller-Plesset perturbation theory, and vibrational configuration interaction (VCI). A VCC calculation typically gives higher accuracy than a corresponding VCI calculation with the same number of parameters and the same formal operation count.
Vibrational spectra of dipropylsulfoxide.
Markarian, Shiraz A; Gabrielian, Liana S; Bonora, Sergio
2007-12-31
FTIR and Raman spectra analysis of pure dipropylsulfoxide (DPSO), binary mixtures of DPSO/CCl(4), and DPSO/water has been first performed. The complex pattern of spectra has been explained on the basis of molecular interactions between DPSO and other molecules and, in the aqueous solutions, the role of both hydrophilic and hydrophobic interactions have been discussed depending on the concentrations. The changes in the intensities and in the frequencies of DPSO bands on concentration have been considered. The curve fitting procedure has been performed for both SO and C-H stretching region, and, on the basis of deconvolution results different type of molecular interactions have been considered. Density function theory DFT/(B3LYP) method has been used to determine the optimized geometry for free DPSO and for 1 DPSO:1 water complex. On the basis of the 6-31+G(d) quality sets parameters, the DFT calculated bond parameters and harmonic vibrations are in a very good agreement with experimental data. PMID:17350885
NASA Astrophysics Data System (ADS)
Arul Dhas, D.; Hubert Joe, I.; Roy, S. D. D.; Balachandran, S.
2013-05-01
An absolute vibrational analysis has been attempted on the basis of experimental FTIR and NIR-FT Raman spectra with calculated vibrational wavenumbers and intensities of phenoxy acetic acids. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers have been calculated with the help of B3LYP method with Dunning correlation consistent basis set aug-cc-pVTZ. The electronic structures of molecular fragments were described in terms of natural bond orbital analysis, which shows intermolecular Osbnd H⋯O and intramolecular Csbnd H⋯O hydrogen bonds. The electronic absorption spectra with different solvents have been investigated in combination with time-dependent density functional theory calculation. The pKa values of phenoxy acetic acids were compared.
Ab initio and DFT studies of the structure and vibrational spectra of anhydrous caffeine
NASA Astrophysics Data System (ADS)
Srivastava, Santosh K.; Singh, Vipin B.
2013-11-01
Vibrational spectra and molecular structure of anhydrous caffeine have been systematically investigated by second order Moller-Plesset (MP2) perturbation theory and density functional theory (DFT) calculations. Vibrational assignments have been made and many previous ambiguous assignments in IR and Raman spectra are amended. The calculated DFT frequencies and intensities at B3LYP/6-311++G(2d,2p) level, were found to be in better agreement with the experimental values. It was found that DFT with B3LYP functional predicts harmonic vibrational wave numbers more close to experimentally observed value when it was performed on MP2 optimized geometry rather than DFT geometry. The calculated TD-DFT vertical excitation electronic energies of the valence excited states of anhydrous caffeine are found to be in consonance to the experimental absorption peaks.
Large amplitude vibrations and damage detection of rectangular plates
NASA Astrophysics Data System (ADS)
Manoach, Emil; Trendafilova, Irina
2008-08-01
In this work, geometrically nonlinear vibrations of fully clamped rectangular plates are used to study the sensitivity of some nonlinear vibration response parameters to the presence of damage. The geometrically nonlinear version of the Mindlin plate theory is used to model the plate behaviour. Damage is represented as a stiffness reduction in a small area of the plate. The plate is subjected to harmonic loading with a frequency of excitation close to the first natural frequency leading to large amplitude vibrations. The plate vibration response is obtained by a pseudo-load mode superposition method. The main results are focussed on establishing the influence of damage on the vibration response of the plate and the change in the time-history diagrams and the Poincar maps caused by the damage. Finally, a criterion and a damage index for detecting the presence and the location of the damage is proposed. The criterion is based on analysing the points in the Poincar sections of the damaged and healthy plate. Numerical results for large amplitude vibrations of damaged and healthy rectangular and square plates are presented and the proposed damage index for the considered cases is calculated. The criterion demonstrates quite good abilities to detect and localize damage.
NASA Astrophysics Data System (ADS)
Shaaban, Ibrahim A.; Hassan, Ahmed E.; Abuelela, Ahmed M.; Zoghaieb, Wajdi M.; Mohamed, Tarek A.
2016-01-01
Raman (3500-55 cm-1) and infrared (4000-300 cm-1) spectra of 2-Amino-5-ethyl-1,3,4-thiadiazole (AET; C4H7N3S) have been recorded in the solid phase. In addition, the 1H and 13C NMR spectra of AET were obtained in DMSO-d6. As a result of internal rotations of either methyl and/or ethyl groups around the C-C bonds with NH2 moiety being planar (sp2) and/or non-planar (sp3) eight structures are theoretically proposed (1-8). The conformational energies and vibrational frequencies have been calculated using Density Functional Theory (DFT) with the methods of B3LYP and B3PW91 utilizing 6-31G (d) and 6-311++G(d,p) basis sets. And then S-4 (the only conformer with real frequencies) was optimized, to yield S-9, however the Thiadiazole ring slightly twisted (tilt angle is 0.9°). The 1H and 13C NMR chemical shifts were also predicted using a GIAO approximation at 6-311++G(d,p) basis set utilizing B3LYP and B3PW91 methods with solvent effects using PCM method. The computational outcomes favor S-9; the methyl group being staggered to the lone pair of N4 and reside trans position to the S atom, whereas NH2 is non-planar in good agreement with the current study. Aided by the above mentioned DFT computations, a complete vibrational assignment of the observed infrared and Raman bands along with NMR chemical shifts has been proposed. The vibrational interpretations have been supported by normal coordinate analysis and potential energy distributions (PEDs). Finally, NH2, CH3 and C2H5 barriers to internal rotations were carried out using B3LYP/6-31G(d) optimized structural parameters (S-9). The results are reported herein and compared with X-ray structural parameters.
NASA Astrophysics Data System (ADS)
Belmonte, D.; Ottonello, G.; Zuccolini, M. Vetuschi
2013-02-01
We present the results of a computational investigation of the structure-energy and vibrational properties of alumina under various aggregation states (crystalline, glassy, and liquid) with ab initio procedures. IV-fold, V-fold, and VI-fold oxygen-coordinated aluminum monomeric forms in a dielectric continuum with dielectric constant ɛ = 4.575 were investigated through DFT/B3LYP gas-phase calculations coupled with a Polarized Continuum Model approach and those of the periodical structure D63d (R-3c) which leads to the α-Al2O3 polymorph of alumina, when subjected to symmetry operations, were investigated with the same functional within the LCAO approximation and in the framework of Bloch's theorem. Based on the computed energies and vibrational features, an aggregate of the D63d positively charged cluster [Al12O11]14+ contoured by [AlO4]5- units in an approximate 1:3 proportion to achieve neutrality satisfactorily reproduce the heat capacity of the liquid within experimental uncertainty. The glass is seen as a wrong accretionary form induced by fast cooling rates and subjected to steric forces that locally modify the coordination state of the central atom. Cessation of rotational and translational movements, only partly counterbalanced by acoustic sine-wave-dispersed and excess phonons, gives rise to the huge heat-capacity gap observed at the glass transition (˜5.3R). When cooling rates are sufficiently slow, the accretion around the D63d seeds follows the structural constraints and the heat capacity of α-alumina is almost perfectly reproduced by the 27 Einstein oscillators coupled with the 3 acoustic terms and the anharmonic corrections.
NASA Astrophysics Data System (ADS)
Brizuela, Alicia B.; Raschi, Ana B.; Castillo, Mara V.; Davies, Lilian; Romano, Elida; Brandn, Silvia A.
2014-09-01
In this study, aqueous solutions at different molar concentrations of sodium cyclamate in water were completely characterized by HATR (Horizontal Attenuated Total Reflectance) and Raman spectroscopies. The theoretical structures of cyclamate ion, the zwitterionic and neutral forms of the cyclamic acid and its dimer were optimized in gas and aqueous solution phases by using the hybrid B3LYP/6-31G* method. The solvent effects for the four species in aqueous solutions were simulated by using self-consistent reaction field (SCRF) calculations employing the integral equation formalism variant (IEFPCM) model. The complete assignments of the vibrational spectra of all the forms of cyclamic acid were performed taking into account the factor group analysis with the Scaled Quantum Mechanics Force Field (SQMFF) methodology. The existence of the zwitterionic and neutral forms of the cyclamic acid and its dimer in a solution of cyclamate in water is evidenced by characteristic bands in the HATR and Raman spectra. The dimerization of cyclamate in aqueous solution was previously reported by conductimetric method. The natural population analysis (NPA) and Merz-Kollman (MK) charges, molecular electrostatic potential (MEP), natural bond orbital (NBO) and atoms in molecules (AIM) calculations predict for all the species the principal donor and acceptor sites for the H bonds formation in aqueous solution. The SQM force fields for the cyclamate ion, the zwitterionic and neutral species of the cyclamic acid were obtained and their corresponding force constants in both phases were reported. Additionally, the solvation energies for those species were reported.
Ribeiro, Fabienne; Iung, Christophe; Leforestier, Claude
2005-08-01
We present a new approach based on the block-Davidson scheme which provides eigenvalues and eigenvectors of highly excited (ro) vibrational states of polyatomic molecules. The key ingredient is a prediagonalized-perturbative scheme applied to a subspace of a curvilinear normal-mode basis set. This approach is coupled to the Jacobi vector description recently developed by our group [C. Leforestier, A. Viel, F. Gatti, C. Munoz, and C. Iung, J. Chem. Phys. 114, 2099 (2001)], and applied to the HFCO and H2CO molecules, which represent the main difficulties of such calculations for any available method. The first one presents a significant state density because of its low symmetry and the presence of a fluorine atom, while strong resonances and intermode couplings occur in H2CO. This study establishes the robustness, the numerical efficiency, and the versatility of the method which is compared to the regular Lanczos and Davidson schemes. It is also shown that the eigenvectors can be obtained within a given accuracy easily set by the user. This point constitutes one of the main advantages of the method as very few potential-energy surfaces achieve an accuracy of the order of a wave number for highly excited states. Furthermore, this method allows one to restrict the calculations to selected energy levels based on their zero-order descriptions. PMID:16108630
Bennett, Charles L.; Sewall, Noel; Boroa, Carl
2014-08-19
An engine based on a reciprocating piston engine that extracts work from pressurized working fluid. The engine includes a harmonic oscillator inlet valve capable of oscillating at a resonant frequency for controlling the flow of working fluid into of the engine. In particular, the inlet valve includes an inlet valve head and a spring arranged together as a harmonic oscillator so that the inlet valve head is moveable from an unbiased equilibrium position to a biased closed position occluding an inlet. Upon releasing the inlet valve the inlet valve head undergoes a single oscillation past the equilibrium positio to a maximum open position and returns to a biased return position close to the closed position to choke the flow and produce a pressure drop across the inlet valve causing the inlet valve to close. Protrusions carried either by the inlet valve head or piston head are used to bump open the inlet valve from the closed position and initiate the single oscillation of the inlet valve head, and protrusions carried either by the outlet valve head or piston head are used to close the outlet valve ahead of the bump opening of the inlet valve.
Refocusing vibrating targets in SAR images
NASA Astrophysics Data System (ADS)
Wang, Qi; Santhanam, Balu; Pepin, Matthew; Atwood, Tom; Hayat, Majeed M.
2012-06-01
In synthetic-aperture radar (SAR) returned signals, ground-target vibrations introduce a phase modulation that is linearly proportional to the vibration displacement. Such modulation, termed the micro-Doppler effect, introduces ghost targets along the azimuth direction in reconstructed SAR images that prevents SAR from forming focused images of the vibrating targets. Recently, a discrete fractional Fourier transform (DFrFT) based method was developed to estimate the vibration frequencies and instantaneous vibration accelerations of the vibrating targets from SAR returned signals. In this paper, a demodulation-based algorithm is proposed to reconstruct focused SAR images of vibrating targets by exploiting the estimation results of the DFrFT-based vibration estimation method. For a single-component harmonic vibration, the history of the vibration displacement is first estimated from the estimated vibration frequency and the instantaneous vibration accelerations. Then a reference signal whose phase is modulated by the estimated vibration displacement with a delay of 180 degree is constructed. After that, the SAR phase history from the vibration target is multiplied by the reference signal and the vibration-induced phase modulation is canceled. Finally, the SAR image containing the re-focused vibration target is obtained by applying the 2-D Fourier transform to the demodulated SAR phase history. This algorithm is applied to simulated SAR data and successfully reconstructs the SAR image containing the re-focused vibrating target.
Nonadiabatic effects on peptide vibrational dynamics induced by conformational changes.
Antony, Jens; Schmidt, Burkhard; Schtte, Christof
2005-01-01
Quantum dynamical simulations of vibrational spectroscopy have been carried out for glycine dipeptide (CH(3)-CO-NH-CH(2)-CO-NH-CH(3)). Conformational structure and dynamics are modeled in terms of the two Ramachandran dihedral angles of the molecular backbone. Potential energy surfaces and harmonic frequencies are obtained from electronic structure calculations at the density functional theory (DFT) [B3LYP/6-31+G(d)] level. The ordering of the energetically most stable isomers (C(7) and C(5)) is reversed upon inclusion of the quantum mechanical zero point vibrational energy. Vibrational spectra of various isomers show distinct differences, mainly in the region of the amide modes, thereby relating conformational structures and vibrational spectra. Conformational dynamics is modeled by propagation of quantum mechanical wave packets. Assuming a directed energy transfer to the torsional degrees of freedom, transitions between the C(7) and C(5) minimum energy structures occur on a sub-picosecond time scale (700...800 fs). Vibrationally nonadiabatic effects are investigated for the case of the coupled, fundamentally excited amide I states. Using a two state-two mode model, the resulting wave packet dynamics is found to be strongly nonadiabatic due to the presence of a seam of the two potential energy surfaces. Initially prepared adiabatic vibrational states decay upon conformational change on a time scale of 200...500 fs with population transfer of more than 50% between the coupled amide I states. Also the vibrational energy transport between localized (excitonic) amide I vibrational states is strongly influenced by torsional dynamics of the molecular backbone where both enhanced and reduced decay rates are found. All these observations should allow the detection of conformational changes by means of time-dependent vibrational spectroscopy. PMID:15638661
Analysis of vibrational-translational energy transfer using the direct simulation Monte Carlo method
NASA Technical Reports Server (NTRS)
Boyd, Iain D.
1991-01-01
A new model is proposed for energy transfer between the vibrational and translational modes for use in the direct simulation Monte Carlo method (DSMC). The model modifies the Landau-Teller theory for a harmonic oscillator and the rate transition is related to an experimental correlation for the vibrational relaxation time. Assessment of the model is made with respect to three different computations: relaxation in a heat bath, a one-dimensional shock wave, and hypersonic flow over a two-dimensional wedge. These studies verify that the model achieves detailed balance, and excellent agreement with experimental data is obtained in the shock wave calculation. The wedge flow computation reveals that the usual phenomenological method for simulating vibrational nonequilibrium in the DSMC technique predicts much higher vibrational temperatures in the wake region.
Vibrational corrections to the second hyperpolarizabilities of AlnPn clusters
NASA Astrophysics Data System (ADS)
Feitoza, Luan; Silveira, Orlando; Castro, Marcos A.; Leão, Salviano A.; Fonseca, Tertius L.
2015-12-01
In this work, we report results of vibrational corrections to the second hyperpolarizabilities of Al2P2, Al3P3, Al4P4, Al6P6, and Al9P9 clusters. The vibrational corrections were calculated through the perturbation theoretic method of Bishop and Kirtman and also using a variational methodology at the second order Møller-Plesset perturbation theory level with the aug-cc-pVDZ basis set. Results show that the vibrational corrections are important, accounting for more than half of the corresponding electronic second hyperpolarizabilities at the static limit. Comparisons between results obtained through both methods show very good agreements for the terms [α2] and [μβ] but significant differences for the term [μ2α]. Dynamic vibrational corrections to the second hyperpolarizabilities related to the dc-second harmonic generation, intensity dependent refractive index, and dc-Kerr nonlinear optical processes are also reported.
NASA Astrophysics Data System (ADS)
Heislbetz, Sandra; Schwerdtfeger, Peter; Rauhut, Guntram
2007-05-01
The impact of approximate normal coordinates for spanning high level potential energy surfaces on vibrational frequencies is studied within the framework of vibrational SCF and configuration interaction calculations (VCI). The use of low level normal coordinates avoids expensive geometry optimizations and harmonic frequency calculations and thus allows for a significant reduction in CPU time. Benchmark calculations are provided for a set of molecules ranging from 5 to 7 atoms. An application to CHFClI and CDFClI shows that this approximation still allows for very accurate results. These molecules are of particular interest for studying parity violation effects.
Thermal weights for semiclassical vibrational response functions
NASA Astrophysics Data System (ADS)
Moberg, Daniel R.; Alemi, Mallory; Loring, Roger F.
2015-08-01
Semiclassical approximations to response functions can allow the calculation of linear and nonlinear spectroscopic observables from classical dynamics. Evaluating a canonical response function requires the related tasks of determining thermal weights for initial states and computing the dynamics of these states. A class of approximations for vibrational response functions employs classical trajectories at quantized values of action variables and represents the effects of the radiation-matter interaction by discontinuous transitions. Here, we evaluate choices for a thermal weight function which are consistent with this dynamical approximation. Weight functions associated with different semiclassical approximations are compared, and two forms are constructed which yield the correct linear response function for a harmonic potential at any temperature and are also correct for anharmonic potentials in the classical mechanical limit of high temperature. Approximations to the vibrational linear response function with quantized classical trajectories and proposed thermal weight functions are assessed for ensembles of one-dimensional anharmonic oscillators. This approach is shown to perform well for an anharmonic potential that is not locally harmonic over a temperature range encompassing the quantum limit of a two-level system and the limit of classical dynamics.
Thermal weights for semiclassical vibrational response functions.
Moberg, Daniel R; Alemi, Mallory; Loring, Roger F
2015-08-28
Semiclassical approximations to response functions can allow the calculation of linear and nonlinear spectroscopic observables from classical dynamics. Evaluating a canonical response function requires the related tasks of determining thermal weights for initial states and computing the dynamics of these states. A class of approximations for vibrational response functions employs classical trajectories at quantized values of action variables and represents the effects of the radiation-matter interaction by discontinuous transitions. Here, we evaluate choices for a thermal weight function which are consistent with this dynamical approximation. Weight functions associated with different semiclassical approximations are compared, and two forms are constructed which yield the correct linear response function for a harmonic potential at any temperature and are also correct for anharmonic potentials in the classical mechanical limit of high temperature. Approximations to the vibrational linear response function with quantized classical trajectories and proposed thermal weight functions are assessed for ensembles of one-dimensional anharmonic oscillators. This approach is shown to perform well for an anharmonic potential that is not locally harmonic over a temperature range encompassing the quantum limit of a two-level system and the limit of classical dynamics. PMID:26328812
Aeroelastic Computations of a Compressor Stage Using the Harmonic Balance Method
NASA Technical Reports Server (NTRS)
Reddy, T. S. R.
2010-01-01
The aeroelastic characteristics of a compressor stage were analyzed using a computational fluid dynamic (CFD) solver that uses the harmonic balance method to solve the governing equations. The three dimensional solver models the unsteady flow field due to blade vibration using the Reynolds-Averaged Navier-Stokes equations. The formulation enables the study of the effect of blade row interaction through the inclusion of coupling modes between blade rows. It also enables the study of nonlinear effects of high amplitude blade vibration by the inclusion of higher harmonics of the fundamental blade vibration frequency. In the present work, the solver is applied to study in detail the aeroelastic characteristics of a transonic compressor stage. Various parameters were included in the study: number of coupling modes, blade row axial spacing, and operating speeds. Only the first vibration mode is considered with amplitude of oscillation in the linear range. Both aeroelastic stability (flutter) of rotor blade and unsteady loading on the stator are calculated. The study showed that for the stage considered, the rotor aerodynamic damping is not influenced by the presence of the stator even when the axial spacing is reduced by nearly 25 percent. However, the study showed that blade row interaction effects become important for the unsteady loading on the stator when the axial spacing is reduced by the same amount.
Gearbox vibration diagnostic analyzer
NASA Technical Reports Server (NTRS)
1992-01-01
This report describes the Gearbox Vibration Diagnostic Analyzer installed in the NASA Lewis Research Center's 500 HP Helicopter Transmission Test Stand to monitor gearbox testing. The vibration of the gearbox is analyzed using diagnostic algorithms to calculate a parameter indicating damaged components.
NASA Technical Reports Server (NTRS)
Kis, Z.; Janszky, J.; Vinogradov, An. V.; Kobayashi, T.
1996-01-01
The optical Schroedinger cat states are simple realizations of quantum states having nonclassical features. It is shown that vibrational analogues of such states can be realized in an experiment of double pulse excitation of vibrionic transitions. To track the evolution of the vibrational wave packet we derive a non-unitary time evolution operator so that calculations are made in a quasi Heisenberg picture.
Yang, Seongeun; Cho, Minhaeng
2009-10-01
The vibrational absorption (IR) and vibrational circular dichroism (VCD) spectra of alanine dipeptide analog in water are directly calculated by Fourier transforming the time correlation functions of the electric and magnetic dipole moments, which are calculated using the dynamic partial charges and trajectory of the peptide generated from the quantum mechanical/molecular mechanical molecular dynamics simulations. The alanine dipeptide analog is treated at the Hartree-Fock level with 3-21G, 4-31G, 6-31G, and 6-31G(*) basis sets and the solvent H(2)O is modeled with the TIP3P water. The atomic partial charges are obtained from the Lowdin population analysis, which gives consistent IR spectral profiles irrespective of the basis sets used. The simulated VCD spectrum by a polyproline II(P(II))-dominant trajectory is compatible with the previous experimental results of the polyproline peptides, where the amide I and II VCD bands are negative couplets with a weak positive peak to the high frequency region. The sampling efficiency of the P(II) conformer is much lower than the other ones at all basis levels used. The simulated VCD spectrum of alpha-helix averaged over five trajectories has the reverse sign pattern compared to the P(II) spectrum and is found to be consistent with the previously observed spectral features of alpha-helical polypeptides. The sign patterns of the beta-strand VCD spectrum are qualitatively similar to the experimental spectra of beta-sheet rich proteins. The VCD spectra obtained from the trajectories containing several extended conformers such as beta and P(II) are not clearly distinguishable from the beta-strand-dominant spectra. It is interesting that the P(II) and the coil VCD spectra coincide in sign pattern and relative intensity for all amide modes. This demonstrates that the negative couplet structures of the amide I and II VCD spectra do not necessarily prove the dominance of either P(II) or coil conformation. We anticipate that the present method can be used to directly simulate the IR and VCD spectra of structurally heterogeneous biomolecules in condensed phases. PMID:19814574
Method and apparatus for vibrating a substrate during material formation
Bailey, Jeffrey A. (Richland, WA) [Richland, WA; Roger, Johnson N. (Richland, WA) [Richland, WA; John, Munley T. (Benton City, WA) [Benton City, WA; Walter, Park R. (Benton City, WA) [Benton City, WA
2008-10-21
A method and apparatus for affecting the properties of a material include vibrating the material during its formation (i.e., "surface sifting"). The method includes the steps of providing a material formation device and applying a plurality of vibrations to the material during formation, which vibrations are oscillations having dissimilar, non-harmonic frequencies and at least two different directions. The apparatus includes a plurality of vibration sources that impart vibrations to the material.
Theoretical studies of high-harmonic generation based on the Keldysh Faisal Reiss theory
NASA Astrophysics Data System (ADS)
Mineo, H.; Nagaya, K.; Hayashi, M.; Lin, S. H.
2007-06-01
We use the Keldysh-Faisal-Reiss (KFR) approach to study the process of high-harmonic generation (HHG) for hydrogen and helium atoms and a hydrogen molecule where the helium atom and hydrogen molecule wavefunctions are described by a 1s single Slater determinant. In this model we directly use the photoionization amplitude calculated by the KFR approach and relate it to the HHG spectra. We plot HHG from hydrogen and helium atoms, and a hydrogen molecule in the presence of a linearly and circularly polarized laser field, and also discuss the nuclear motion corrections for the hydrogen molecule, which are calculated under the Frank-Condon (FC) approximation by using both displaced-distorted harmonic oscillators and Morse wavefunctions. Contributions from each vibrational state are also discussed.
NASA Technical Reports Server (NTRS)
Green, C.
1971-01-01
Guidelines of the methods and applications used in vibration technology at the MSFC are presented. The purpose of the guidelines is to provide a practical tool for coordination and understanding between industry and government groups concerned with vibration of systems and equipments. Topics covered include measuring, reducing, analyzing, and methods for obtaining simulated environments and formulating vibration specifications. Methods for vibration and shock testing, theoretical aspects of data processing, vibration response analysis, and techniques of designing for vibration are also presented.
Calculation of multi-layer plate damper under one-axial load
NASA Astrophysics Data System (ADS)
Hui, Yan; Lu, Zhang; Hong-Yuan, Jiang; Alexander, M. Ulanov
2016-02-01
A multi-layer damper with waved plates under one-axial load is considered. A method of theoretical calculation of its energy dissipation coefficient is proposed. An experimental research of own frequencies and vibration transfer ratios for different parameters of damper structure, harmonic vibration load and random load is performed. Results of this research are approximated by functions; it is possible to use these functions for the calculation of the damper too. Project supported by the Programme of Introducing Talents of Discipline to Universities (Grant No. B07018).
Liu, Zhongqiang; Zhang, Xianxi; Zhang, Yuexing; Li, Renjie; Jiang, Jianzhuang
2006-10-01
A theoretical investigation of the fully optimized geometries and electronic structures of the metal-free (TPdPzH(2)), N,N'-dideuterio (TPdPzD(2)), and magnesium (TPdPzMg) tetra-2,3-pyridino-porphyrazine has been conducted based on density functional theory. The optimized geometries at density functional theory level for these compounds are reported here for the first time. A comparison between the different molecules for the geometry, molecular orbital, and atomic charge is made. The substituent effect of the N atoms on the molecular structures of these compounds is discussed. The IR and Raman spectra for these three compounds have also been calculated at density functional B3LYP level using the 6-31G(d) basis set. Detailed assignments of the NH, NM, and pyridine ring vibrational bands in the IR and Raman spectra have been made based on assistance of animated pictures. The simulated IR spectra of TPdPzH(2) are compared with the experimental absorption spectra, and very good consistency has been found. The isotope effect on the IR and Raman spectra is also discussed. PMID:16524765
Welsch, Ralph Manthe, Uwe
2014-08-07
The mode-selective chemistry of the title reaction is studied by full-dimensional quantum dynamics simulation on an accurate ab initio potential energy surface for vanishing total angular momentum. Using a rigorous transition state based approach and multi-configurational time-dependent Hartree wave packet propagation, initial state-selected reaction probabilities for many ro-vibrational states of methane are calculated. The theoretical results are compared with experimental trends seen in reactions of methane. An intuitive interpretation of the ro-vibrational control of the chemical reactivity provided by a sudden model based on the quantum transition state concept is discussed.
NASA Astrophysics Data System (ADS)
Hetma?czyk, Joanna; Hetma?czyk, ?ukasz; Migda?-Mikuli, Anna; Mikuli, Edward
2015-02-01
The vibrational and reorientational motions of NH3 ligands and ClO4- anions were investigated by Fourier transform middle-infrared spectroscopy (FT-IR) in the high- and low-temperature phases of [Mn(NH3)6](ClO4)2. The temperature dependencies of full width at half maximum (FWHM) of the infrared bands at: 591 and 3385 cm-1, associated with: ?r(NH3) and ?as(N-H) modes, respectively, indicate that there exist fast (correlation times ?R ? 10-12-10-13 s) reorientational motions of NH3 ligands, with a mean values of activation energies: 7.8 and 4.5 kJ mol-1, in the phase I and II, respectively. These reorientational motions of NH3 ligands are only slightly disturbed in the phase transition region and do not significantly contribute to the phase transition mechanism. Fourier transform far-infrared and middle-infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at TCc = 137.6 K (on cooling), which suggested lowering of the crystal structure symmetry. Infrared spectra of [Mn(NH3)6](ClO4)2 were recorded and interpreted by comparison with respective theoretical spectra calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311 + G(d,p) basis set (on H, N, Cl, O atoms) for the isolated equilibrium two models (Model 1 - separate isolated [Mn(NH3)6]2+ cation and ClO4- anion and Model 2 - [Mn(NH3)6(ClO4)2] complex system). Calculated optical spectra show a good agreement with the experimental infrared spectra (FT-FIR and FT-MIR) for the both models.
NASA Astrophysics Data System (ADS)
Krishnakumar, V.; Prabavathi, N.
2010-09-01
This work deals with the vibrational spectroscopy of 6,7-dimethoxy-1,4-dihydro-1,3-quinoxalinedione by means of quantum chemical calculations. The mid and far FT-IR and FT-Raman spectra are recorded in the condensed State. The fundamental vibrational frequencies and intensity of vibrational bands are evaluated using density functional theory (DFT) with the standard B3LYP/6-31G* method and basis set combination and is scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectrum is interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results of the calculations are applied to simulate infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra. The infrared unscaled frequencies and intensities are used to disentangle the role played by back-donation in the title compound. For this purpose five other molecules are considered as references: ethane, dimethyl ether, anisole, p-nitro-anisole, and p-hydroxyanisole, in which back-donation has already been ascertained also experimentally. From the study of infrared intensities it is shown that no back-donation of electrons from the oxygen lone pairs takes place, independently of the conformation of the methoxy-group.
Analysis of a high Tc superconducting levitation system with vibration isolation control
Nagaya, Kosuke
1996-03-01
This paper presents a method for controlling vibrations of a levitated high Tc superconducting body subjected to base disturbances. To have the control forces, an actuator consisting of a permanent magnet with an electromagnet was presented. The analytical solution for calculating levitation forces due to the permanent magnet and the control currents in the electromagnet was obtained. The levitation forces obtained coincide with the previously published results. The equation of motion of the levitated body subjected to base disturbances under the control was presented. Nonlinear vibrations of the body were first discussed; then the method of vibration isolation control using the direct disturbance cancellation combining the velocity feedback control was investigated. Numerical calculations were carried out for the levitation forces, with respect to the levitated body subjected to harmonic or pulse base excitations. It was clarified that the present method is valid for controlling nonlinear systems like the magnetic levitated superconducting body.
The Harmonic Balance Method with Arc-Length Continuation in Rotor/stator Contact Problems
NASA Astrophysics Data System (ADS)
VON GROLL, G.; EWINS, D. J.
2001-03-01
There are a variety of abnormal running conditions in rotating machinery which lead to rotor/stator interaction dynamics which, in turn, can cause a rich mixture of effects associated with rub-related phenomena. These effects manifest themselves in the occurrence of multiple solutions for steady state vibration response scenarios, including amplitude jumps during rotor acceleration, and vibration responses at different/multiple frequencies of excitation forces such as unbalance. This paper describes a numerical algorithm based on the harmonic balance method to calculate the periodic response of a non-linear system under periodic excitation. The algorithm also calculates the stability of the periodic solutions found, marks turning and bifurcation points, and follows a solution branch over varying system parameters via arc-length continuation.
Non-Empirical Anharmonic Analysis of Vibrational States of BF3 and BH3 Using Symmetry Coordinates
NASA Astrophysics Data System (ADS)
Pitsevich, G. A.; Malevich, A. E.; Sleptsov, E. U.; Sapeshko, V. V.
2015-03-01
Force fields, anharmonic constant matrices, and harmonic and anharmonic frequencies of vibrational states of BF3 and BH3 were calculated using B3LYP/cc-pVTZ/cc-pVQZ/cc-pV5Z/acc-pV5Z approximations. Anharmonic IR spectra of the molecules were calculated by the vibrational self-consistent field (VSCF) method included in the quantum chemistry package GAMESS. Frequencies of totally symmetric stretching vibrations were refined by constructing potential surfaces using symmetry coordinates. The Schroedinger equation transformed into symmetry coordinates was solved numerically using construction followed by diagonalization of the Hamiltonian matrix. It was shown that the last approach reproduced the experimental vibrational frequencies for BF3 more accurately than those obtained in the anharmonic approximation. The frequencies of the totally symmetric stretching vibration of BH3, which is especially interesting because of the lack of experimental data, that were calculated in the harmonic and anharmonic approximations and by constructing potential surfaces were 2565, 2503, and 2539 cm-1, respectively.
Dixon, D.A.; Chase, B.E.; Fitzgerald, G.; Matsuzawa, Nobuyuki
1995-03-30
The harmonic vibrational frequencies of C{sub 60} have been calculated at the local density functional level by using analytic second derivatives. The calculated values for the observed infrared and Raman transitions are in good agreement with the experimental values and suggest that there are a number of misassigned bands based on thick film infrared and Raman measurements. The calculated transitions have been used to provide tentative assignments to the peaks observed by inelastic neutron scattering and high-resolution electron-energy-loss spectroscopy. 31 refs., 4 tabs.
A vibrational spectroscopy study on anserine and its aqueous solutions.
Akkaya, Y; Balci, K; Goren, Y; Akyuz, S; Stricker, M C; Stover, D D; Ritzhaupt, G; Collier, W B
2015-10-01
In this study based on vibrational spectroscopic measurements and Density Functional Theory (DFT), we aimed for a reliable interpretation of the IR and Raman spectra recorded for anserine in the solid phase and water (H2O) and heavy water (D2O) solutions. Initial DFT calculations at the B3LYP/6-31G(d) searched possible conformers of the anserine zwitterion using a systematic conformational search. The corresponding equilibrium geometrical parameters and vibrational spectral data were determined for each of the stable conformers (in water) by the geometry optimization and hessian calculations performed at the same level of theory using the polarized continuum model (PCM). The same calculations were repeated to determine the most energetically preferred dimer structure for the molecule and the associated geometry, force field and vibrational spectral data. The harmonic force constants obtained from these calculations were scaled by the Scaled Quantum Mechanical Force Field (SQM) method and then used in the calculation of the refined wavenumbers, potential energy distributions, IR and Raman intensities. These refined theoretical data, which confirm the zwitterion structure for anserine in the solid phase or aqueous solvents, revealed the remarkable effects of intermolecular hydrogen bonding on the structural properties and observed IR and Raman spectra of this molecule. PMID:25997178
NASA Technical Reports Server (NTRS)
Grigoryey, N. V.; Fedorovich, M. A.
1973-01-01
The vibroacoustical characteristics of different types of electric motors are discussed. It is shown that the basic source of low frequency vibrations is rotor unbalance. A flexible damping support, with an antivibrator, is used to obtain the vibroacoustical effect of reduction in the basic harmonic of the electric motor. A model of the electric motor and the damping apparatus is presented. Mathematical models are developed to show the relationships of the parameters. The basic purpose in using a calculation model id the simultaneous replacement of the exciting force created by the rotor unbalance and its inertial rigidity characteristics by a limiting kinematic disturbance.
NASA Astrophysics Data System (ADS)
Ramkumaar, G. R.; Srinivasan, S.; Bhoopathy, T. J.; Gunasekaran, S.
2012-12-01
The solid phase FT-IR and FT-Raman spectra of zidovudine (AZT) were recorded in the regions 4000-400 and 3500-100 cm-1, respectively. The optimized geometry, frequency and intensity of the vibrational bands of zidovudine were obtained by the Restricted Hartree-Fock (RHF) density functional theory (DFT) with complete relaxation in the potential energy surface using 6-31G(d,p) basis set. The harmonic vibrational frequencies for zidovudine were calculated and the scaled values have been compared with experimental values of FTIR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. The harmonic vibrational wave numbers and intensities of vibrational bands of zidovudine with its cation and anion were calculated and compared with the neutral AZT. The DFT calculated HOMO and LUMO energies shows that charge transfer occurs within the molecule. The electron density-based local reactivity descriptors such as Fukui functions were calculated to explain the chemical selectivity or reactivity site in AZT.
The Study of Nonlinear Vibration Analysis of Rotor System Using Component Mode Synthesis Method
NASA Astrophysics Data System (ADS)
Iwatsubo, Takuzo; Shimbo, Kenichi; Kawamura, Shozo
In this paper, an effective method for the nonlinear vibration analysis of rotor systems is proposed using the Component Mode Synthesis method and the harmonic balance method. In the method, the system is divided into components and the differential equations for each frequency and component is derived. The equation of motion for the whole system, then, is obtained using the Component Mode Synthesis method. The dynamic analysis of a rotor system is carried out using the harmonic balance method. The distinguishing feature of the proposed method is that the nonlinear restoring force term is expressed using modal coordinate system in a convenient form. The order of the modal equation of motion and calculation time, therefore, can be reduced. In the numerical example, it is shown that the analysis method proposed in this paper is effective for the nonlinear vibration analysis of rotor systems.
Sunspots and Their Simple Harmonic Motion
ERIC Educational Resources Information Center
Ribeiro, C. I.
2013-01-01
In this paper an example of a simple harmonic motion, the apparent motion of sunspots due to the Sun's rotation, is described, which can be used to teach this subject to high-school students. Using real images of the Sun, students can calculate the star's rotation period with the simple harmonic motion mathematical expression.
NASA Technical Reports Server (NTRS)
Payne, M. H.
1973-01-01
A computer program is described for the calculation of the zeroes of the associated Legendre functions, Pnm, and their derivatives, for the calculation of the extrema of Pnm and also the integral between pairs of successive zeroes. The program has been run for all n,m from (0,0) to (20,20) and selected cases beyond that for n up to 40. Up to (20,20), the program (written in double precision) retains nearly full accuracy, and indications are that up to (40,40) there is still sufficient precision (4-5 decimal digits for a 54-bit mantissa) for estimation of various bounds and errors involved in geopotential modelling, the purpose for which the program was written.
Sharkey, Keeper L.; Kirnosov, Nikita; Adamowicz, Ludwik
2015-05-07
Direct variational calculations where the Born-Oppenheimer approximation is not assumed are done for all rovibrational states of the D{sub 2} molecule corresponding to first excited rotational level (the N = 1 states). All-particle explicitly correlated Gaussian basis functions are used in the calculations. The exponential parameters of the Gaussians are optimized with the aid of analytically calculated energy gradient determined with respect to these parameters. The results allow to determine the ortho-para spin isomerization energies as a function of the vibrational quantum number.
Futami, Yoshisuke; Ozaki, Yasushi; Ozaki, Yukihiro
2016-02-21
Infrared (IR) and near infrared (NIR) spectra were measured for methanol and the methanol-pyridine complex in carbon tetrachloride. Upon the formation of the methanol-pyridine complex, the frequencies of both the fundamental and first overtone bands of the OH stretching vibration shifted to lower frequencies, and the absorption intensity of the fundamental increased significantly, while that of the first overtone decreased markedly. By using quantum chemical calculations, we estimated the absorption intensities and frequencies of the fundamental and first overtone bands for the OH stretching vibration based on the one-dimensional Schrödinger equation. The calculated results well reproduced the experimental results. The molecular vibration potentials and dipole moment functions of the OH stretching vibration modes were compared between methanol and the methanol-pyridine complex in terms of absorption intensity changes and frequency shifts. The large change in the dipole moment function was found to be the main cause for the variations in absorption intensity for the fundamental and first overtone bands. PMID:26862859
NASA Astrophysics Data System (ADS)
Li, Ying-Cheng; Chuang, Hsiao-Han; Tan, Jake Acedera; Takahashi, Kaito; Kuo, Jer-Lai
2014-06-01
Recent experimental observations of (H_2O)_3^+, (H_2O)_3^+Ar, H^+(H_2O)_3, and H^+(H_2O)_3Ar clusters in the region 1400-3800 wn show that the OH stretching vibration has distinct characteristics. Multidimensional normal mode calculations were carried out for OH stretching vibrations in the 1200-4000 wn photon energy range. The potential energy and dipole surfaces were evaluated by using first-principles methods. By comparing the calculated frequencies and intensities of OH stretching vibration with experimental spectra, we found that the assignment of OH strecthing of H_3O^+ moiety and free OH strectching vibration have resonable agreement with experimental data. Jeffrey M. Headrick, Eric G. Diken, Richard S. Walters, Nathan I. Hammer, Richard A. Christie, Jun Cui, Evgeniy M. Myshakin, Michael A. Duncan, Mark A. Johnson, Kenneth D. Jordan, Science, 2005, 17, 1765. Kenta Mizuse, Jer-Lai Kuo and Asuka Fujii, Chem. Sci., 2011, 2, 868 Kenta Mizuse and Asuka Fujii, J. Phys. Chem. A, 2013, 117, 929.
Kucharska, E; Michalski, J; Sąsiadek, W; Talik, Z; Bryndal, I; Hanuza, J
2013-04-15
The crystal and molecular structures of 6-methyl-3-nitro-2-(2-phenylhydrazinyl)pyridine (6-methyl-3-nitro-2-phenylhydrazopyridine) have been determined by X-ray diffraction and quantum chemical DFT analysis. The crystal is monoclinic, space group C2/c, with Z=8 formula units in the elementary unit cell of dimensions a=16.791(4), b=6.635(2), c=21.704(7)Å, β=100.54(3)°. The molecule consists of two nearly planar pyridine subunits. A conformation of the linking hydrazo-bridge CNHNHC is bend and the dihedral angle between the planes of the phenyl and pyridine rings is 88.2(5)°. The hydrogen bonding of the type NH···N and possibly also CH···O favors a dimer formation in the crystal structure. The dimers are further linked by a NH···O hydrogen bond, so forming a layer parallel to the ab plane. The molecular structure of the studied compound has been determined using the DFT B3LYP/6-311G(2d,2p) approach and compared to that derived from X-ray studies. The IR and Raman wavenumbers have been calculated for the optimized geometry of a possible monomer structural model but the possibility of the dimer formation through the NH···N hydrogen bond has also been considered. The structural and vibrational properties of the intra-molecular NH···O interaction are described. PMID:23434560
Non-Equilibrium Casimir Force between Vibrating Plates
Hanke, Andreas
2013-01-01
We study the fluctuation-induced, time-dependent force between two plates confining a correlated fluid which is driven out of equilibrium mechanically by harmonic vibrations of one of the plates. For a purely relaxational dynamics of the fluid we calculate the fluctuation-induced force generated by the vibrating plate on the plate at rest. The time-dependence of this force is characterized by a positive lag time with respect to the driving. We obtain two distinctive contributions to the force, one generated by diffusion of stress in the fluid and another related to resonant dissipation in the cavity. The relation to the dynamic Casimir effect of the electromagnetic field and possible experiments to measure the time-dependent Casimir force are discussed. PMID:23326401
Non-equilibrium Casimir force between vibrating plates.
Hanke, Andreas
2013-01-01
We study the fluctuation-induced, time-dependent force between two plates confining a correlated fluid which is driven out of equilibrium mechanically by harmonic vibrations of one of the plates. For a purely relaxational dynamics of the fluid we calculate the fluctuation-induced force generated by the vibrating plate on the plate at rest. The time-dependence of this force is characterized by a positive lag time with respect to the driving. We obtain two distinctive contributions to the force, one generated by diffusion of stress in the fluid and another related to resonant dissipation in the cavity. The relation to the dynamic Casimir effect of the electromagnetic field and possible experiments to measure the time-dependent Casimir force are discussed. PMID:23326401
Color harmonization for images
NASA Astrophysics Data System (ADS)
Tang, Zhen; Miao, Zhenjiang; Wan, Yanli; Wang, Zhifei
2011-04-01
Color harmonization is an artistic technique to adjust a set of colors in order to enhance their visual harmony so that they are aesthetically pleasing in terms of human visual perception. We present a new color harmonization method that treats the harmonization as a function optimization. For a given image, we derive a cost function based on the observation that pixels in a small window that have similar unharmonic hues should be harmonized with similar harmonic hues. By minimizing the cost function, we get a harmonized image in which the spatial coherence is preserved. A new matching function is proposed to select the best matching harmonic schemes, and a new component-based preharmonization strategy is proposed to preserve the hue distribution of the harmonized images. Our approach overcomes several shortcomings of the existing color harmonization methods. We test our algorithm with a variety of images to demonstrate the effectiveness of our approach.
Molecular structure, vibrational spectroscopy, NBO and HOMO, LUMO studies of o-methoxybenzonitrile
NASA Astrophysics Data System (ADS)
Elanthiraiyan, M.; Jayasudha, B.; Arivazhagan, M.
2015-01-01
In the present study, the FT-IR and FT-Raman spectra of o-methoxybenzonitrile (O-MBN) have been recorded in the region 4000-400 cm-1 and 3500-50 cm-1, respectively. The fundamental modes of vibrational frequencies of O-MBN are assigned. Theoretical information on the optimized geometry, harmonic vibrational frequencies, infrared and Raman intensities were obtained by means of ab initio Hartree-Fock (HF) and density functional theory (DFT) gradient calculations with complete relaxation in the potential energy surface using 6-311++G(d,p) basis set. The vibrational frequencies which were determined experimentally from the spectral data are compared with those obtained theoretically from ab initio and DFT calculations. A close agreement was achieved between the observed and calculated frequencies by refinement of the scale factors. The infrared and Raman spectra were also predicted from the calculated intensities. Thermodynamic properties like entropy, heat capacity, zero point energy, have been calculated for the molecule. The predicted first hyperpolarizability also shows that the molecule might have a reasonably good non-linear optical (NLO) behavior. The calculated HOMO-LUMO energy gap reveals that charge transfer occurs within the molecule. Stability of the molecule arising from hyper conjugative interactions, charge delocalization have been analyzed using natural bond orbitals (NBO) analysis. Unambiguous vibrational assignment of all the fundamentals was made using the total energy distribution (TED).
Cacciatore, M.; Billing G.D.
1992-01-09
The authors present calculations of vibration-vibration and vibration-translation energy transfer rate constants in diatom-diatom collisions. The results are compared to recent experimental measurements.
Spectroscopic analysis and DFT calculations of a food additive carmoisine.
Snehalatha, M; Ravikumar, C; Hubert Joe, I; Sekar, N; Jayakumar, V S
2009-04-01
FT-IR and Raman techniques were employed for the vibrational characterization of the food additive Carmoisine (E122). The equilibrium geometry, various bonding features, and harmonic vibrational wavenumbers have been investigated with the help of density functional theory (DFT) calculations. A good correlation was found between the computed and experimental wavenumbers. Azo stretching wavenumbers have been lowered due to conjugation and pi-electron delocalization. Predicted electronic absorption spectra from TD-DFT calculation have been analysed comparing with the UV-vis spectrum. The first hyperpolarizability of the molecule is calculated. Intramolecular charge transfer (ICT) responsible for the optical nonlinearity of the dye molecule has been discussed theoretically and experimentally. Stability of the molecule arising from hyperconjugative interactions, charge delocalization and C-H ...O, improper, blue shifted hydrogen bonds have been analysed using natural bond orbital (NBO) analysis. PMID:19124271
Spectroscopic analysis and DFT calculations of a food additive Carmoisine
NASA Astrophysics Data System (ADS)
Snehalatha, M.; Ravikumar, C.; Hubert Joe, I.; Sekar, N.; Jayakumar, V. S.
2009-04-01
FT-IR and Raman techniques were employed for the vibrational characterization of the food additive Carmoisine (E122). The equilibrium geometry, various bonding features, and harmonic vibrational wavenumbers have been investigated with the help of density functional theory (DFT) calculations. A good correlation was found between the computed and experimental wavenumbers. Azo stretching wavenumbers have been lowered due to conjugation and ?-electron delocalization. Predicted electronic absorption spectra from TD-DFT calculation have been analysed comparing with the UV-vis spectrum. The first hyperpolarizability of the molecule is calculated. Intramolecular charge transfer (ICT) responsible for the optical nonlinearity of the dye molecule has been discussed theoretically and experimentally. Stability of the molecule arising from hyperconjugative interactions, charge delocalization and C-H⋯O, improper, blue shifted hydrogen bonds have been analysed using natural bond orbital (NBO) analysis.
NASA Technical Reports Server (NTRS)
Corrigan, J. C.; Cronkhite, J. D.; Dompka, R. V.; Perry, K. S.; Rogers, J. P.; Sadler, S. G.
1989-01-01
Under a research program designated Design Analysis Methods for VIBrationS (DAMVIBS), existing analytical methods are used for calculating coupled rotor-fuselage vibrations of the AH-1G helicopter for correlation with flight test data from an AH-1G Operational Load Survey (OLS) test program. The analytical representation of the fuselage structure is based on a NASTRAN finite element model (FEM), which has been developed, extensively documented, and correlated with ground vibration test. One procedure that was used for predicting coupled rotor-fuselage vibrations using the advanced Rotorcraft Flight Simulation Program C81 and NASTRAN is summarized. Detailed descriptions of the analytical formulation of rotor dynamics equations, fuselage dynamic equations, coupling between the rotor and fuselage, and solutions to the total system of equations in C81 are included. Analytical predictions of hub shears for main rotor harmonics 2p, 4p, and 6p generated by C81 are used in conjunction with 2p OLS measured control loads and a 2p lateral tail rotor gearbox force, representing downwash impingement on the vertical fin, to excite the NASTRAN model. NASTRAN is then used to correlate with measured OLS flight test vibrations. Blade load comparisons predicted by C81 showed good agreement. In general, the fuselage vibration correlations show good agreement between anslysis and test in vibration response through 15 to 20 Hz.
Free vibrations of delaminated beams
NASA Technical Reports Server (NTRS)
Shen, M.-H. H.; Grady, J. E.
1992-01-01
Free vibration of laminated composite beams is studied. The effect of interply delaminations on natural frequencies and mode shapes is evaluated both analytically and experimentally. A generalized vibrational principle is used to formulate the equation of motion and associated boundary conditions for the free vibration of a composite beam with a delamination of arbitrary size and location. The effect of coupling between longitudinal vibration and bending vibration is considered. This coupling effect is shown to significantly affect the calculated natural frequencies and mode shapes of the delaminated beam.
Vibrational averages along thermal lines
NASA Astrophysics Data System (ADS)
Monserrat, Bartomeu
2016-01-01
A method is proposed for the calculation of vibrational quantum and thermal expectation values of physical properties from first principles. Thermal lines are introduced: these are lines in configuration space parametrized by temperature, such that the value of any physical property along them is approximately equal to the vibrational average of that property. The number of sampling points needed to explore the vibrational phase space is reduced by up to an order of magnitude when the full vibrational density is replaced by thermal lines. Calculations of the vibrational averages of several properties and systems are reported, namely, the internal energy and the electronic band gap of diamond and silicon, and the chemical shielding tensor of L-alanine. Thermal lines pave the way for complex calculations of vibrational averages, including large systems and methods beyond semilocal density functional theory.
NASA Astrophysics Data System (ADS)
Topper, Robert Q.; Zhang, Qi; Liu, Yi-Ping; Truhlar, Donald G.
1993-03-01
Converged quantum mechanical vibrational-rotational partition functions and free energies are calculated using realistic potential energy surfaces for several chalcogen dihydrides (H2O, D2O, H2S, H2Se) over a wide range of temperatures (600-4000 K). We employ an adaptively optimized Monte Carlo integration scheme for computing vibrational-rotational partition functions by the Fourier path-integral method. The partition functions and free energies calculated in this way are compared to approximate calculations that assume the separation of vibrational motions from rotational motions. In the approximate calculations, rotations are treated as those of a classical rigid rotator, and vibrations are treated by perturbation theory methods or by the harmonic oscillator model. We find that the perturbation theory treatments yield molecular partition functions which agree closely overall (within 7%) with the fully coupled accurate calculations, and these treatments reduce the errors by about a factor of 2 compared to the independent-mode harmonic oscillator model (with errors of 16%). These calculations indicate that vibrational anharmonicity and mode-mode coupling effects are significant, but that they may be treated with useful accuracy by perturbation theory for these molecules. The quantal free energies for gaseous water agree well with previously available approximate values for this well studied molecule, and similarly accurate values are also presented for the less well studied D2O, H2S, and H2Se.
Simple Harmonic Motion in Harmonic Plane Waves.
ERIC Educational Resources Information Center
Benumof, Reuben
1980-01-01
Discusses the distribution of kinetic and potential energy in transverse and longitudinal waves and examines the transmission of power and momentum. This discussion is intended to aid in understanding the simple harmonic motion of a particle involved in the propagation of a harmonic mechanical plane wave. (HM)
Vibrational Spectra and Heat Capacity of Methane, and the Speed of Sound
NASA Astrophysics Data System (ADS)
Tennis, Ronald; Bailey, Ryan; Henderson, Giles
2000-12-01
A two-part physical chemistry laboratory experiment is described in which students evaluate statistical mechanical theory by comparing a measured speed of sound and heat capacity with values predicted from vibrational spectra. In part 1 students measure the IR spectrum of CH4(g) and the Raman spectrum of CH4(l) to determine quantized vibrational energy spacings. Strong Raman scattering of a pulsed nitrogen laser beam is observed with a liquid methane sample in a custom cryogenic cell constructed from two side-arm test tubes and a length of Pyrex tube. These data are used with the statistical mechanics of a harmonic oscillator to calculate vibrational heat capacities and CP/CV; of CH4(g) and the speed of sound in CH4(g). In part 2, the predicted speed of sound is compared with an experimental value measured with a simple acoustic resonance cavity (Kundt's tube) exhausted to a Bunsen burner.
Diao, Chuan-Ling; Wang, Chun-Hai; Lu, Jing; Luo, Neng-Neng; Jing, Xi-Ping E-mail: xpjing@pku.edu.cn; Qi, Ze-Ming; Shao, Tao; Wang, Yu-Yin; Wang, Quan-Chao; Kuang, Xiao-Jun; Fang, Liang; Shi, Feng E-mail: xpjing@pku.edu.cn
2014-03-21
1:2 B-site cation ordered Ba(Mg{sub 1/3}Nb{sub 2/3})O{sub 3} ceramic was synthesized using conventional solid-state reaction at 1600?C for 12?h. The structure parameters were obtained through Rietveld refinement of X-ray diffraction data. The Raman peak frequencies were obtained by Lorenz fitting on Raman spectrum. Four-parameter semiquantum model was used to fit the infrared (IR) reflectivity spectrum, and the fitted parameters were used to calculate the dielectric permittivity ? and dielectric loss tan?. A total of 9 active Raman and 16 active IR modes were obtained using first-principle calculations based on density functional theory with local density approximation. All of the vibrational modes were assigned and represented by linear combinations of the symmetry coordinates deduced using group theory analysis. The Raman mode with the highest frequency A{sub 1g}{sup (4)} (789?cm{sup ?1}) can be described as the breathing vibration of NbO{sub 6}. The IR modes E{sub u}{sup (1)} (149?cm{sup ?1}) and A{sub 2u}{sup (2)} (212?cm{sup ?1}), which can be described as the twisting vibrations of BaMgO{sub 6}/BaNbO{sub 6} on the ab plane and the stretching vibrations of BaMgO{sub 6}/BaNbO{sub 6} along the c direction, respectively, are the dominant contributing modes to ? and tan?. The dielectric property parameters obtained using IR spectrum fittings, first-principal calculations, and microwave measurements were compared.
Experimental and DFT studies on the vibrational and electronic spectra of 9-anthracenemethanol.
Kou, Shanshan; Zhou, Hu; Tang, Guodong; Li, Rongqing; Zhang, Yu; Zhao, Jianying; Wei, Changmei
2012-10-01
Vibrational spectral measurements were made for 9-anthracenemethanol. Optimized geometrical structure and harmonic vibration frequencies were computed based on ab initio and density functional theory B3LYP methods using 6-311G(**) and LANL2DZ basis sets. The equilibrium geometries got from all of the methods and basis were compared with X-ray diffraction results. The IR and UV-vis spectra of the title compound were computed using all of the methods and choose the most appropriate way to discuss. And the absorption spectra were calculated both in gas phase and in CH(3)CH(2)OH and CH(3)CN solution. The calculated results matched well with the experimental values. On the basis, the first excited state electronic transition energy has been calculated using time-dependent density functional theory. PMID:22885894
NASA Astrophysics Data System (ADS)
Uma Maheswari, J.; Muthu, S.; Sundius, Tom
2013-05-01
The present work aims at exploring the vibrational spectra of Isosorbide dinitrate and its chemical activity in a five membered ring system. The FT-IR and FT-Raman spectral studies of the Isosorbide dinitrate (ISDN) were carried out. The equilibrium geometry, various bonding features and harmonic vibrational frequencies of ISDN have been calculated using B3LYP density functional theory (DFT) with 6-31G(d, p) as basis set. The calculated HOMO and LUMO energies and density of states (DOS) show the chemical activity of the molecule. Good correlations between the experimental 1H and 13C NMR chemical shifts in methanol-d and calculated GIAO shielding tensors were found. The potential energy surface was studied using the DFT method.
Fedorov, Dmitry A.; Varganov, Sergey A.; Derevianko, Andrei
2014-05-14
We calculate the potential energy curves, the permanent dipole moment curves, and the lifetimes of the ground and excited vibrational states of the heteronuclear alkali dimers XY (X, Y = Li, Na, K, Rb, Cs) in the X{sup 1}?{sup +} electronic state using the coupled cluster with singles doubles and triples method. All-electron quadruple-? basis sets with additional core functions are used for Li and Na, and small-core relativistic effective core potentials with quadruple-? quality basis sets are used for K, Rb, and Cs. The inclusion of the coupled cluster non-perturbative triple excitations is shown to be crucial for obtaining the accurate potential energy curves. A large one-electron basis set with additional core functions is needed for the accurate prediction of permanent dipole moments. The dissociation energies are overestimated by only 14 cm{sup ?1} for LiNa and by no more than 114 cm{sup ?1} for the other molecules. The discrepancies between the experimental and calculated harmonic vibrational frequencies are less than 1.7 cm{sup ?1}, and the discrepancies for the anharmonic correction are less than 0.1 cm{sup ?1}. We show that correlation between atomic electronegativity differences and permanent dipole moment of heteronuclear alkali dimers is not perfect. To obtain the vibrational energies and wave functions the vibrational Schrdinger equation is solved with the B-spline basis set method. The transition dipole moments between all vibrational states, the Einstein coefficients, and the lifetimes of the vibrational states are calculated. We analyze the decay rates of the vibrational states in terms of spontaneous emission, and stimulated emission and absorption induced by black body radiation. In all studied heteronuclear alkali dimers the ground vibrational states have much longer lifetimes than any excited states.
NASA Astrophysics Data System (ADS)
Fedorov, Dmitry A.; Derevianko, Andrei; Varganov, Sergey A.
2014-05-01
We calculate the potential energy curves, the permanent dipole moment curves, and the lifetimes of the ground and excited vibrational states of the heteronuclear alkali dimers XY (X, Y = Li, Na, K, Rb, Cs) in the X1?+ electronic state using the coupled cluster with singles doubles and triples method. All-electron quadruple-? basis sets with additional core functions are used for Li and Na, and small-core relativistic effective core potentials with quadruple-? quality basis sets are used for K, Rb, and Cs. The inclusion of the coupled cluster non-perturbative triple excitations is shown to be crucial for obtaining the accurate potential energy curves. A large one-electron basis set with additional core functions is needed for the accurate prediction of permanent dipole moments. The dissociation energies are overestimated by only 14 cm-1 for LiNa and by no more than 114 cm-1 for the other molecules. The discrepancies between the experimental and calculated harmonic vibrational frequencies are less than 1.7 cm-1, and the discrepancies for the anharmonic correction are less than 0.1 cm-1. We show that correlation between atomic electronegativity differences and permanent dipole moment of heteronuclear alkali dimers is not perfect. To obtain the vibrational energies and wave functions the vibrational Schrdinger equation is solved with the B-spline basis set method. The transition dipole moments between all vibrational states, the Einstein coefficients, and the lifetimes of the vibrational states are calculated. We analyze the decay rates of the vibrational states in terms of spontaneous emission, and stimulated emission and absorption induced by black body radiation. In all studied heteronuclear alkali dimers the ground vibrational states have much longer lifetimes than any excited states.
Ab initio calculation and anharmonic force field of hypochlorous acid, HOCl
NASA Astrophysics Data System (ADS)
Halonen, L.; Ha, T.-K.
1988-03-01
Ab initio calculations on HOCl have been performed at the third-order Mller-Plesset perturbation theory level to determine the equilibrium structure and the anharmonic force field. An empirical anharmonic force field based on the ab initio results is obtained using available experimental vibration-rotation data. Four of the six harmonic and six of the ten cubic force constants have been determined experimentally, the remaining values being fixed at the ab initio values. A good fit to the experimental vibration-rotation data of four isotopic species is obtained.
Vibrational spectroscopy of astrophysical species
NASA Astrophysics Data System (ADS)
Wang, Yun
Identifications of the species responsible for the unidentified interstellar infrared (UIR) emission bands and the diffuse interstellar absorption (DIB) bands are the two of the major challenges in astrochemistry today. Polycyclic aromatic hydrocarbons (PAHs) have been proposed as the carriers of both signals. Carbon chain clusters and metals have both been detected in the interstellar medium. In this dissertation, reactions of iron with PAHs, and metals (copper, silver and gold) with carbon clusters were investigated. Matrix isolation spectroscopy coupled with density functional (DFT) calculations have been employed throughout this research. Laser ablated iron atoms and evaporated or sublimed benzene, naphthalene, fluorene, pyrene, or coronene were trapped together in solid Ar at 12K. Neutral Fe(benzene), Fe(benzene) 2 , Fe(naphthalene), Fe(fluorene), Fe(pyrene) and Fe (coronene) complexes were formed in the experiments and their infrared absorption spectra obtained. Theoretical calculations of the equilibrium geometries, stabilities, and harmonic vibrational frequencies of these complexes have been carried out using density functional theory. The calculations show that the dissociation energies (D 0 ) of neutral Fe(PAH) complexes are substantially smaller than their cationic counterparts, indicating that the neutral complexes are less tightly bonded. Reactions of laser-ablated metal (copper, silver and gold) atoms with carbon clusters were investigated in excess argon matrices. Fourier transform infrared absorption spectra, with the assistance of 13 C-isotopic substitution experiments and comparison with theoretical calculation, have led to the identification of near-linear CuC 3 , AgC 3 and AuC 3 clusters. Photo-induced isotopic scrambling was observed in the Cu 1213 C 3 clusters and explained via a computed potential energy surface (PES) of this reaction. The mechanism for the photoscrambling is shown to involve the formation of a bicyclic CuC 3 isomer. The formation of small metal-carbon clusters, Cu m C n and Ag m C n (m=1, 2; n=1-3) were also explored theoretically.
Harmonization of Biodiesel Specifications
Alleman, T. L.
2008-02-01
Worldwide biodiesel production has grown dramatically over the last several years. Biodiesel standards vary across countries and regions, and there is a call for harmonization. For harmonization to become a reality, standards have to be adapted to cover all feedstocks. Additionally, all feedstocks cannot meet all specifications, so harmonization will require standards to either tighten or relax. For harmonization to succeed, the biodiesel market must be expanded with the alignment of test methods and specification limits, not contracted.
NASA Astrophysics Data System (ADS)
Tanak, Hasan; Toy, Mehmet
2016-01-01
The molecular geometry and vibrational frequencies of 1-[N-(2-pyridyl)aminomethylidene}-2(1H)-Naphtalenone in the ground state have been calculated by using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-311++G(d,p) basis set. The results of the optimized molecular structure are presented and compared with the experimental X-ray diffraction. The computed vibrational frequencies were used to determine the types of molecular motions associated with each of the experimental bands observed. In addition, calculated results are related to the linear correlation plot of computed data versus experimental geometric parameters and IR data. From the results it was concluded that the B3LYP method is superior to the HF method for the vibrational frequencies. Using the time-dependent density functional theory (TD-DFT) and Hartree-Fock (TD-HF) methods, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method and experimental ones is determined.
Tanak, Hasan; Toy, Mehmet
2016-01-01
The molecular geometry and vibrational frequencies of 1-[N-(2-pyridyl)aminomethylidene}-2(1H)-Naphtalenone in the ground state have been calculated by using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-311++G(d,p) basis set. The results of the optimized molecular structure are presented and compared with the experimental X-ray diffraction. The computed vibrational frequencies were used to determine the types of molecular motions associated with each of the experimental bands observed. In addition, calculated results are related to the linear correlation plot of computed data versus experimental geometric parameters and IR data. From the results it was concluded that the B3LYP method is superior to the HF method for the vibrational frequencies. Using the time-dependent density functional theory (TD-DFT) and Hartree-Fock (TD-HF) methods, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method and experimental ones is determined. PMID:25468437
Polyatomic molecule vibrations
NASA Technical Reports Server (NTRS)
1976-01-01
Polyatomic molecule vibrations are analyzed as harmonic vibrations along normal coordinates. The energy eigenvalues are found for linear and nonlinear symmetric triatomic molecules for valence bond models of the potential function with arbitrary coupling coefficients; such models can usually be fitted to observed energy levels with reasonably good accuracy. Approximate normal coordinates for the H2O molecule are discussed. Degenerate vibrational modes such as occur in CO2 are analyzed and expressions for Fermi resonance between close-lying states of the same symmetry are developed. The bending modes of linear triatomic molecules are expressed in terms of Laguerre polynomials in cylindrical coordinates as well as in terms of Hermite polynomials in Cartesian coordinates. The effects of large-amplitude bending such as occur in the C3 molecule are analyzed, along with anharmonic effects, which split the usually degenerate bending mode energy levels. Finally, the vibrational frequencies, degeneracies, and symmetry properties of XY3, X2Y2, and XY4 type molecules are discussed.
Molecular docking, spectroscopic studies and quantum calculations on nootropic drug.
Uma Maheswari, J; Muthu, S; Sundius, Tom
2014-04-01
A systematic vibrational spectroscopic assignment and analysis of piracetam [(2-oxo-1-pyrrolidineacetamide)] have been carried out using FT-IR and FT-Raman spectral data. The vibrational analysis was aided by an electronic structure calculation based on the hybrid density functional method B3LYP using a 6-311G++(d,p) basis set. Molecular equilibrium geometries, electronic energies, IR and Raman intensities, and harmonic vibrational frequencies have been computed. The assignments are based on the experimental IR and Raman spectra, and a complete assignment of the observed spectra has been proposed. The UV-visible spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies and the maximum absorption wavelengths ?max were determined by the time-dependent DFT (TD-DFT) method. The geometrical parameters, vibrational frequencies and absorption wavelengths were compared with the experimental data. The complete vibrational assignments are performed on the basis of the potential energy distributions (PED) of the vibrational modes in terms of natural internal coordinates. The simulated FT-IR, FT-Raman, and UV spectra of the title compound have been constructed. Molecular docking studies have been carried out in the active site of piracetam by using Argus Lab. In addition, the potential energy surface, HOMO and LUMO energies, first-order hyperpolarizability and the molecular electrostatic potential have been computed. PMID:24487180
The harmonic oscillator and nuclear physics
NASA Technical Reports Server (NTRS)
Rowe, D. J.
1993-01-01
The three-dimensional harmonic oscillator plays a central role in nuclear physics. It provides the underlying structure of the independent-particle shell model and gives rise to the dynamical group structures on which models of nuclear collective motion are based. It is shown that the three-dimensional harmonic oscillator features a rich variety of coherent states, including vibrations of the monopole, dipole, and quadrupole types, and rotations of the rigid flow, vortex flow, and irrotational flow types. Nuclear collective states exhibit all of these flows. It is also shown that the coherent state representations, which have their origins in applications to the dynamical groups of the simple harmonic oscillator, can be extended to vector coherent state representations with a much wider range of applicability. As a result, coherent state theory and vector coherent state theory become powerful tools in the application of algebraic methods in physics.
Characteristic of torsional vibration of mill main drive excited by electromechanical coupling
NASA Astrophysics Data System (ADS)
Zhang, Yifang; Yan, Xiaoqiang; Lin, Qihui
2016-01-01
In the study of electromechanical coupling vibration of mill main drive system, the influence of electrical system on the mechanical transmission is considered generally, however the research for the mechanism of electromechanical interaction is lacked. In order to research the electromechanical coupling resonance of main drive system on the F3 mill in a plant, the cycloconverter and synchronous motor are modeled and simulated by the MTLAB/SIMULINK firstly, simulation result show that the current harmonic of the cycloconverter can lead to the pulsating torque of motor output. Then the natural characteristics of the mechanical drive system are calculated by ANSYS, the result show that the modal frequency contains the component which is close to the coupling vibration frequency of 42Hz. According to the simulation result of the mechanical and electrical system, the closed loop feedback model including the two systems are built, and the mechanism analysis of electromechanical coupling presents that there is the interaction between the current harmonic of electrical system and the speed of the mechanical drive system. At last, by building and computing the equivalent nonlinear dynamics model of the mechanical drive system, the dynamic characteristics of system changing with the stiffness, damping coefficient and the electromagnetic torque are obtained. Such electromechanical interaction process is suggested to consider in research of mill vibration, which can induce strong coupling vibration behavior in the rolling mill drive system.
NASA Astrophysics Data System (ADS)
Balachandran, V.; Parimala, K.
2012-10-01
Two purine tautomers of 2-amino-6-chloropurine (ACP), in labeled as N9H10 and N7H10, were investigated by vibrational spectroscopy and quantum chemical method. The FT-IR and FT-Raman spectra of ACP have been recorded in the regions 4000-400 cm-1 and 3500-100 cm-1, respectively. The measured spectra were interpreted by aid of a normal coordinate analysis following DFT full geometry optimization and vibrational frequency calculations at B3LYP/6-311++G(d,p) level. First-order hyperpolarizability, HOMO and LUMO energies were calculated at same level of theory. The calculated molecular geometry has been compared with the X-ray data. The observed and calculated frequencies were found in good agreement. The obtained NBO data and second-order perturbation energy values to elucidate the Lewis and non-Lewis types of bonding structures in the purine tautomer N9H10, have indicated the presence of an intramolecular hyperconjucative interaction between lone pair N and N-C bond orbital.
NASA Technical Reports Server (NTRS)
Chin, G.; Weaver, H. A.
1984-01-01
The vibrational and rotational excitation of the CO molecule in cometary comae were investigated using a model which includes IR vibrational pumping by the solar flux, vibrational and rotational radiative decay, and collisional coupling among rotational states. Steady state was not assumed in solving the rate equations. The evolution of a shell of CO gas was monitored as it expanded from the nucleus into the outer coma. Collisional effects were treated using a kinetic temperature profile derived from theoretical work on the coma energy balance. The kinetic temperature was assumed to be extremely cold in the inner coma; this has significant consequences for the CO excitation. If optical depth effects are ignored, only low J transitions will be significantly excited in comets observed at high spatial resolution. Ground-based observations of CO co-vibrational and rotational transitions will be extremely difficult due to lack of sensitivity and/or terrestrial absorption. However, CO should be detectable from a large comet with favorable observing geometry if the CO is a parent molecule present at the 10% level (or greater) relative to H2O. Observations using cooled, spaceborne instruments should be capable of detecting CO emission from even moderately bright comets.
Vibrational spectroscopy of resveratrol
NASA Astrophysics Data System (ADS)
Billes, Ferenc; Mohammed-Ziegler, Ildikó; Mikosch, Hans; Tyihák, Ernő
2007-11-01
In this article the authors deal with the experimental and theoretical interpretation of the vibrational spectra of trans-resveratrol (3,5,4'-trihydroxy- trans-stilbene) of diverse beneficial biological activity. Infrared and Raman spectra of the compound were recorded; density functional calculations were carried out resulting in the optimized geometry and several properties of the molecule. Based on the calculated force constants, a normal coordinate analysis yielded the character of the vibrational modes and the assignment of the measured spectral bands.
Vibrational spectroscopic study and NBO analysis on tranexamic acid using DFT method.
Muthu, S; Prabhakaran, A
2014-08-14
In this work, we reported the vibrational spectra of tranexamic acid (TA) by experimental and quantum chemical calculation. The solid phase FT-Raman and FT-IR spectra of the title compound were recorded in the region 4000 cm(-1) to 100 cm(-1) and 4000 cm(-1) to 400 cm(-1) respectively. The molecular geometry, harmonic vibrational frequencies and bonding features of TA in the ground state have been calculated by using density functional theory (DFT) B3LYP method with standard 6-31G(d,p) basis set. The scaled theoretical wavenumber showed very good agreement with the experimental values. The vibrational assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes. Stability of the molecule, arising from hyperconjugative interactions and charge delocalization, has been analyzed using Natural Bond Orbital (NBO) analysis. The results show that ED in the ?(*) and ?(*) antibonding orbitals and second order delocalization energies E(2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. The electrostatic potential mapped onto an isodensity surface has been obtained. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The thermodynamic properties (heat capacity, entropy, and enthalpy) of the title compound at different temperatures were calculated in gas phase. PMID:24747330
Vibrational spectroscopic study and NBO analysis on tranexamic acid using DFT method
NASA Astrophysics Data System (ADS)
Muthu, S.; Prabhakaran, A.
2014-08-01
In this work, we reported the vibrational spectra of tranexamic acid (TA) by experimental and quantum chemical calculation. The solid phase FT-Raman and FT-IR spectra of the title compound were recorded in the region 4000 cm-1 to 100 cm-1 and 4000 cm-1 to 400 cm-1 respectively. The molecular geometry, harmonic vibrational frequencies and bonding features of TA in the ground state have been calculated by using density functional theory (DFT) B3LYP method with standard 6-31G(d,p) basis set. The scaled theoretical wavenumber showed very good agreement with the experimental values. The vibrational assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes. Stability of the molecule, arising from hyperconjugative interactions and charge delocalization, has been analyzed using Natural Bond Orbital (NBO) analysis. The results show that ED in the ?* and ?* antibonding orbitals and second order delocalization energies E(2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. The electrostatic potential mapped onto an isodensity surface has been obtained. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The thermodynamic properties (heat capacity, entropy, and enthalpy) of the title compound at different temperatures were calculated in gas phase.
Harmonics generated from a DC biased transformer
Shu Lu; Yilu Liu; Ree, J. De La . The Bradley Dept. of Electrical Engineering)
1993-04-01
The paper presents harmonic characteristics of transformer excitation currents under DC bias caused by geomagnetically induced currents (GIC). A newly developed saturation model of a single phase shell form transformer based on 3D finite element analysis is used to calculate the excitation currents. As a consequence, the complete variations of excitation current harmonics with respect to an extended range of GIC bias are revealed. The results of this study are useful in understanding transformers as harmonic sources and the impact on power systems during a solar magnetic disturbance.
Coupling between plate vibration and acoustic radiation
NASA Technical Reports Server (NTRS)
Frendi, Abdelkader; Maestrello, Lucio; Bayliss, Alvin
1992-01-01
A detailed numerical investigation of the coupling between the vibration of a flexible plate and the acoustic radiation is performed. The nonlinear Euler equations are used to describe the acoustic fluid while the nonlinear plate equation is used to describe the plate vibration. Linear, nonlinear, and quasi-periodic or chaotic vibrations and the resultant acoustic radiation are analyzed. We find that for the linear plate response, acoustic coupling is negligible. However, for the nonlinear and chaotic responses, acoustic coupling has a significant effect on the vibration level as the loading increases. The radiated pressure from a plate undergoing nonlinear or chaotic vibrations is found to propagate nonlinearly into the far-field. However, the nonlinearity due to wave propagation is much weaker than that due to the plate vibrations. As the acoustic wave propagates into the far-field, the relative difference in level between the fundamental and its harmonics and subharmonics decreases with distance.
On the vibrational spectra of HSO and SOH
NASA Astrophysics Data System (ADS)
Denis, Pablo A.
2009-05-01
The harmonic and fundamental vibrational frequencies, rotational constants, vibration-rotation corrections and Zero point energies of HSO and SOH and their deuterated isomers (DSO and SOD) have been determined employing the CCSD(T) methodology in conjunction with the aug-cc-pV(X+d)Z and cc-pwCVQZ basis sets. The calculated fundamental frequencies of SOH are 830, 1150 and 3577 cm -1, for the ?SO, ?bend and ?OH, respectively. In the case of HSO the computed fundamentals are 1002, 1077 and 2335 cm -1, for the ?SO, ?bend and ?SH, respectively. The values are discussed in terms of the experimental determinations available. The rotational constants reported for HSO are in reasonable agreement with experiment; the computed values are 301,271, 20,557 and 19,192 MHz. In the case of SOH, for the first time, we report the rotational constants including vibration-rotation corrections, they are: 654,236, 16,621, 16,178 MHz. The force fields calculated allowed as to estimate accurate ZPEs, the suggested values are 6.48 and 8.19 kcal/mol for HSO and SOH, respectively. Finally, we recommend the following structural parameters for HSO rSO = 1.4924 , rSH = 1.3649 and ?HSO = 104.76; whereas for SOH we recommend rSO = 1.6302 , rOH = 0.9629 and ?SOH = 107.97.
VIBRATIONALLY EXCITED C{sub 6}H
Gottlieb, C. A.; McCarthy, M. C.; Thaddeus, P.
2010-08-15
Rotational spectra of the linear carbon chain radical C{sub 6}H in two low-lying excited vibrational states were observed both at millimeter wavelengths in a low-pressure glow discharge and at centimeter wavelengths in a supersonic molecular beam. Two series of harmonically related lines with rotational constants within 0.3% of the {sup 2{Pi}} ground state were assigned to the {sup 2{Sigma}} and {sup 2{Delta}} vibronic components of an excited bending vibrational level. Measurements of the intensities of the lines in the glow discharge indicate that the {sup 2{Sigma}} component lies very close to ground, but the {sup 2{Delta}} component is much higher in energy. The standard Hamiltonian for an isolated {sup 2{Delta}} state with five spectroscopic constants reproduces the observed rotational spectrum, but several high-order distortion terms in the spin-rotation interaction are needed to reproduce the spectrum of the {sup 2{Sigma}} component in C{sub 6}H and C{sub 6}D. The derived spectroscopic constants allow astronomers to calculate the rotational spectra of the {sup 2{Sigma}} and {sup 2{Delta}} states up to 260 GHz to within 0.1 km s{sup -1} or better in equivalent radial velocity.