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1

Calculation of harmonic and anharmonic vibrational wavenumbers for triatomic uranium compounds XUY  

NASA Astrophysics Data System (ADS)

The performance of nine different variants of density functional theory (DFT) for the calculation of the vibrational frequencies of the triatomic compounds UO 22+, NUN, NUO + and CUO is investigated and compared with the predictions obtained with the CASPT2 method [Chem. Phys. Lett. 331 (2000) 229]. Vibrational anharmonicity is calculated for UO 22+ and for CUO and is shown to be small for these systems. A detailed comparison of experimental data obtained in rare-gas matrices with the DFT predictions shows that while the performance of hybrid DFT is uneven, the more "elementary" GGA versions such as PW91 perform extremely well, as the estimated unsigned (signed) average errors are only 11 (-2) cm -1 for the five observed IR bands. Overall, the DFT/GGA results for the closed-shell compounds considered here are at least as good as those yielded by the CASPT2 method, which is computationally much more demanding. Calculated IR intensities are in at least semi-quantitative agreement with experiment. We suggest that the vibrational data becoming available for actinide compounds could and should be used to obtain more reliable parameters in hybrid versions of DFT. The calculated harmonic stretching force constants are shown to depend critically on the U-X bond length, but they are almost insensitive to the method used for their calculation, at a given distance. Observed vibrational spectra can therefore be used to infer reliable bond lengths.

Clavaguéra-Sarrio, Carine; Ismail, Nina; Marsden, Colin J.; Bégué, Didier; Pouchan, Claude

2004-07-01

2

Harmonic calculations and measurements of the irreversibility field using a vibrating sample magnetometer  

E-print Network

magnetometer Ian J. Daniel and Damian P. Hampshire Department of Physics, Superconductivity Group, University inhomogeneity of the magnet on a vibrating sample magnetometer VSM measure- ment of a superconductor measurements on superconductors using a Vi- brating Sample Magnetometer12 VSM . Harmonic VSM measurements

Hampshire, Damian

3

Efficient procedure for the numerical calculation of harmonic vibrational frequencies based on internal coordinates  

SciTech Connect

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.

Miliordos, Evangelos; Xantheas, Sotiris S.

2013-08-15

4

Calculation and analysis of the harmonic vibrational frequencies in molecules at extreme pressure: Methodology and diborane as a test case  

NASA Astrophysics Data System (ADS)

We present a new quantum chemical method for the calculation of the equilibrium geometry and the harmonic vibrational frequencies of molecular systems in dense medium at high pressures (of the order of GPa). The new computational method, named PCM-XP, is based on the polarizable continuum model (PCM), amply used for the study of the solvent effects at standard condition of pressure, and it is accompanied by a new method of analysis for the interpretation of the mechanisms underpinning the effects of pressure on the molecular geometries and the harmonic vibrational frequencies. The PCM-XP has been applied at the density functional theory level to diborane as a molecular system under high pressure. The computed harmonic vibrational frequencies as a function of the pressure have shown a satisfactory agreement with the corresponding experimental results, and the parallel application of the method of analysis has reveled that the effects of the pressure on the equilibrium geometry can be interpreted in terms of direct effects on the electronic charge distribution of the molecular solutes, and that the effects on the harmonic vibrational frequencies can be described in terms of two physically distinct effects of the pressure (curvature and relaxation) on the potential energy for the motion of the nuclei.

Cammi, R.; Cappelli, C.; Mennucci, B.; Tomasi, J.

2012-10-01

5

Calculation and analysis of the harmonic vibrational frequencies in molecules at extreme pressure: methodology and diborane as a test case.  

PubMed

We present a new quantum chemical method for the calculation of the equilibrium geometry and the harmonic vibrational frequencies of molecular systems in dense medium at high pressures (of the order of GPa). The new computational method, named PCM-XP, is based on the polarizable continuum model (PCM), amply used for the study of the solvent effects at standard condition of pressure, and it is accompanied by a new method of analysis for the interpretation of the mechanisms underpinning the effects of pressure on the molecular geometries and the harmonic vibrational frequencies. The PCM-XP has been applied at the density functional theory level to diborane as a molecular system under high pressure. The computed harmonic vibrational frequencies as a function of the pressure have shown a satisfactory agreement with the corresponding experimental results, and the parallel application of the method of analysis has reveled that the effects of the pressure on the equilibrium geometry can be interpreted in terms of direct effects on the electronic charge distribution of the molecular solutes, and that the effects on the harmonic vibrational frequencies can be described in terms of two physically distinct effects of the pressure (curvature and relaxation) on the potential energy for the motion of the nuclei. PMID:23083153

Cammi, R; Cappelli, C; Mennucci, B; Tomasi, J

2012-10-21

6

Molecular structure, Normal Coordinate Analysis, harmonic vibrational frequencies, Natural Bond Orbital, TD-DFT calculations and biological activity analysis of antioxidant drug 7-hydroxycoumarin  

NASA Astrophysics Data System (ADS)

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.

Sebastian, S.; Sylvestre, S.; Jayarajan, D.; Amalanathan, M.; Oudayakumar, K.; Gnanapoongothai, T.; Jayavarthanan, T.

2013-01-01

7

Molecular structure, Normal Coordinate Analysis, harmonic vibrational frequencies, Natural Bond Orbital, TD-DFT calculations and biological activity analysis of antioxidant drug 7-hydroxycoumarin.  

PubMed

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

Sebastian, S; Sylvestre, S; Jayarajan, D; Amalanathan, M; Oudayakumar, K; Gnanapoongothai, T; Jayavarthanan, T

2013-01-15

8

Application of higher harmonic blade feathering for helicopter vibration reduction  

NASA Technical Reports Server (NTRS)

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.

Powers, R. W.

1978-01-01

9

Higher Harmonic Control for Tiltrotor Vibration Reduction  

NASA Technical Reports Server (NTRS)

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.

Nixon, Mark W.; Kvaternik, Raymond G.; Settle, T. Ben

1997-01-01

10

Tiltrotor Vibration Reduction Through Higher Harmonic Control  

NASA Technical Reports Server (NTRS)

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.

Nixon, Mark W.; Kvaternik, Raymond G.; Settle, T. Ben

1997-01-01

11

Harmonic Debye-Waller analysis of anharmonic vibrations  

NASA Astrophysics Data System (ADS)

We address the error resulting from application of the harmonic Debye-Waller factor to anharmonic vibrations. The mean-square atomic displacement determined from the harmonic analysis is compared to values obtained from an exact anharmonic analysis. In the case of strong anharmonicity, we find that the harmonic approximation introduces at most a ˜25% error. The temperature dependence determined from the harmonic analysis follows that found from the exact anharmonic analysis. Errors introduced by the harmonic approximation are comparable in magnitude to the usual systematic errors associated with diffraction experiments and Rietveld refinements.

Safarik, D. J.; Llobet, A.; Lashley, J. C.

2012-05-01

12

Calculation of vibrational transition frequencies and intensities in water dimer: comparison of different vibrational approaches.  

PubMed

We have calculated frequencies and intensities of fundamental and overtone vibrational transitions in water and water dimer with use of different vibrational methods. We have compared results obtained with correlation-corrected vibrational self-consistent-field theory and vibrational second-order perturbation theory both using normal modes and finally with a harmonically coupled anharmonic oscillator local mode model including OH-stretching and HOH-bending local modes. The coupled cluster with singles, doubles, and perturbative triples ab initio method with augmented correlation-consistent triple-zeta Dunning and atomic natural orbital basis sets has been used to obtain the necessary potential energy and dipole moment surfaces. We identify the strengths and weaknesses of these different vibrational approaches and compare our results to the available experimental results. PMID:18407701

Kjaergaard, Henrik G; Garden, Anna L; Chaban, Galina M; Gerber, R Benny; Matthews, Devin A; Stanton, John F

2008-05-01

13

Modeling Stretching Modes of Common Organic Molecules with the Quantum Mechanical Harmonic Oscillator: An Undergraduate Vibrational Spectroscopy Laboratory Exercise  

ERIC Educational Resources Information Center

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.

Parnis, J. Mark; Thompson, Matthew G. K.

2004-01-01

14

Harmonic Motion Detection in a Vibrating Scattering Medium  

PubMed Central

Elasticity imaging is an emerging medical imaging modality that seeks to map the spatial distribution of tissue stiffness. Ultrasound radiation force excitation and motion tracking using pulse-echo ultrasound have been used in numerous methods. Dynamic radiation force is used in vibrometry to cause an object or tissue to vibrate, and the vibration amplitude and phase can be measured with exceptional accuracy. This paper presents a model that simulates harmonic motion detection in a vibrating scattering medium incorporating 3-D beam shapes for radiation force excitation and motion tracking. A parameterized analysis using this model provides a platform to optimize motion detection for vibrometry applications in tissue. An experimental method that produces a multifrequency radiation force is also presented. Experimental harmonic motion detection of simultaneous multifrequency vibration is demonstrated using a single transducer. This method can accurately detect motion with displacement amplitude as low as 100 to 200 nm in bovine muscle. Vibration phase can be measured within 10° or less. The experimental results validate the conclusions observed from the model and show multifrequency vibration induction and measurements can be performed simultaneously. PMID:18986892

Urban, Matthew W.; Chen, Shigao; Greenleaf, James F.

2008-01-01

15

Calculating Buckling And Vibrations Of Lattice Structures  

NASA Technical Reports Server (NTRS)

BUNVIS-RG computer program designed to calculate vibration frequencies or buckling loads of prestressed lattice structures used in outer space. For buckling and vibration problems, BUNVIS-RG calculates deadload axial forces caused in members by any combination of externally-applied static point forces and moments at nodes, axial preload or prestrain in members, and such acceleration loads as those due to gravity. BUNVIS-RG is FORTRAN 77 computer program implemented on CDC CYBER and VAX computer.

Anderson, M. S.; Durling, B. J.; Herstrom, C. L.; Williams, F. W.; Banerjee, J. R.; Kennedy, D.; Warnaar, D. B.

1989-01-01

16

Calculated rotation-vibration energies for HOC +  

NASA Astrophysics Data System (ADS)

We use the ab initio potential surfaces discussed in the immediately preceding paper, with the nonrigid bender Hamiltonian, to calculate rotation-vibration energies for the ground electronic state of HOC +. The results obtained agree with the currently available experimental rotational energy level separations in four HOC + isotopes to within 0.03%. The predicted rotation-vibration energy separations should be of assistance in the experimental search for the corresponding transitions.

Bunker, P. R.; Jensen, Per; Kraemer, W. P.; Beardsworth, R.

1987-02-01

17

Calculated rotation-vibration energies for HOC+  

Microsoft Academic Search

We use the ab initio potential surfaces discussed in the immediately preceding paper, with the nonrigid bender Hamiltonian, to calculate rotation-vibration energies for the ground electronic state of HOC+. The results obtained agree with the currently available experimental rotational energy level separations in four HOC+ isotopes to within 0.03%. The predicted rotation-vibration energy separations should be of assistance in the

P. R. Bunker; Per Jensen; W. P. Kraemer; R. Beardsworth

1987-01-01

18

Vibrational spectra and DFT calculations of squalene  

NASA Astrophysics Data System (ADS)

The isoprenoid compound squalene is a building block molecule for the production of essential cellular molecules such as membrane sterols, has several therapeutic activities including anticancer properties, and has commercial applications for a variety of industries including the production of cosmetics. While the physical structure of squalene has been known for many years, a spectroscopic understanding of the squalene molecular structure and how these spectrometric properties relate to the physical squalene structure has yet to be reported. In the present work we present the Raman and infrared spectra of liquid squalene, complemented by DFT calculations. The molecule has 234 vibrational frequencies and these have been categorized according to the different types of vibrational modes present. The vibrational modes are highly mixed and these have been assigned for the more prominent infrared and Raman bands.

Chun, Hye Jin; Weiss, Taylor L.; Devarenne, Timothy P.; Laane, Jaan

2013-01-01

19

Effect of acoustic coupling on random and harmonic plate vibrations  

NASA Technical Reports Server (NTRS)

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.

Frendi, Abdelkader; Robinson, Jay

1993-01-01

20

Optimized coordinates in vibrational coupled cluster calculations  

SciTech Connect

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.

Thomsen, Bo; Christiansen, Ove [Department of Chemistry, University of Aarhus, DK-8000 Aarhus C (Denmark)] [Department of Chemistry, University of Aarhus, DK-8000 Aarhus C (Denmark); Yagi, Kiyoshi [Theoretical Molecular Science Laboratory and iTHES, RIKEN, Hirosawa 2-1, Saitama 351-0198 (Japan)] [Theoretical Molecular Science Laboratory and iTHES, RIKEN, Hirosawa 2-1, Saitama 351-0198 (Japan)

2014-04-21

21

Vibrational spectroscopy and relaxation of an anharmonic oscillator coupled to harmonic bath.  

PubMed

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. PMID:21639460

Joutsuka, Tatsuya; Ando, Koji

2011-05-28

22

Heat Conduction in a One-Dimensional Harmonic Chain with Three-Dimensional Vibrations  

E-print Network

Heat Conduction in a One-Dimensional Harmonic Chain with Three-Dimensional Vibrations Zonghua LIU1 chain connected by three-dimensional (3D) harmonic springs, the coefficient of heat conduction changes where the coefficient is independent of the lattice constant. KEYWORDS: heat conduction, harmonic chain

Li, Baowen

23

Definitions of non-stationary vibration power for time-frequency analysis and computational algorithms based upon harmonic wavelet transform  

NASA Astrophysics Data System (ADS)

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.

Heo, YongHwa; Kim, Kwang-joon

2015-02-01

24

Influence of vibrational states on high-order-harmonic generation and an isolated attosecond pulse from a N2 molecule  

NASA Astrophysics Data System (ADS)

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.

Guo, Jing; Ge, Xin-Lei; Zhong, Huiying; Zhao, Xi; Zhang, Meixia; Jiang, Yuanfei; Liu, Xue-Shen

2014-11-01

25

Hyperpolarizabilities of the methanol molecule: A CCSD calculation including vibrational corrections.  

PubMed

In this work we present the results for hyperpolarizabilities of the methanol molecule including vibrational corrections and electron correlation effects at the CCSD level. Comparisons to random phase approximation results previously reported show that the electron correlation is in general important for both electronic contribution and vibrational corrections. The role played by the anharmonicities on the calculations of the vibrational corrections has also been analyzed and the obtained results indicate that the anharmonic terms are important for the dc-Pockels and dc-Kerr effects. For the other nonlinear optical properties studied the double-harmonic approximation is found to be suitable. Comparison to available experimental result in gas phase for the dc-second harmonic generation second hyperpolarizability shows a very good agreement with the electronic contribution calculated here while our total value is 14% larger than the experimental value. PMID:20095739

Dutra, Adriano S; Castro, Marcos A; Fonseca, Tertius L; Fileti, Eudes E; Canuto, Sylvio

2010-01-21

26

Algebraic-matrix calculation of vibrational levels of triatomic molecules.  

PubMed

We introduce an accurate and efficient algebraic technique for the computation of the vibrational spectra of triatomic molecules, of both linear and bent equilibrium geometry. The full three-dimensional potential energy surface (PES), which can be based on entirely ab initio data, is parametrized as a product Morse-cosine expansion, expressed in bond angle internal coordinates, and includes explicit interactions among the local modes. We describe the stretching degrees of freedom in the framework of a Morse-type expansion on a suitable algebraic basis, which provides exact analytical expressions for the elements of a sparse Hamiltonian matrix. Likewise, we use a cosine power expansion on a spherical harmonics basis for the bending degree of freedom. The resulting matrix representation in the product space is very sparse, and vibrational levels and eigenfunctions can be obtained by efficient diagonalization techniques. We apply this method to carbonyl sulfide, hydrogen cyanide, water, and nitrogen dioxide. When we base our calculations on high-quality PESs tuned to the experimental data, the computed spectra are in very good agreement with the observed band origins. PMID:19419231

Sedivcová-Uhlíková, T; Abdullah, Hewa Y; Manini, Nicola

2009-05-28

27

Effect of nuclear vibration on high-order-harmonic generation of aligned H2 + molecules  

NASA Astrophysics Data System (ADS)

High-order-harmonic generation (HHG) spectra have been calculated for H2 + molecules aligned parallel to the polarization of the laser field. We make use of the Jacobi coordinates and neglect the rotation of the nuclei. The remaining time-dependent Schrödinger equation is three dimensional in spatial coordinates, one of them being the internuclear separation and the other two describing the electronic motion. The problem is solved using the accurate and efficient time-dependent generalized pseudospectral method in prolate spheroidal coordinates for the electronic coordinates and Fourier grid method for the internuclear separation. Laser pulses with a carrier wavelength of 800 nm, a duration of ten optical cycles, and a peak intensity of 2 ×1014 W/cm2 have been used in the calculations. Our HHG spectra, which incorporate the effect of nuclear vibration, generally exhibit a significant deviation from those calculated for the fixed internuclear separations. The low-energy regions of the spectra, however, resemble those for the nuclei fixed at larger separations, while the high-energy regions are closer to those for the nuclei fixed at smaller internuclear distances. The dynamics of the nuclear vibrational wave packet is also obtained and analyzed.

Telnov, Dmitry A.; Heslar, John; Chu, Shih-I.

2014-12-01

28

HVDC-AC system interaction from AC harmonics. Volume 1. Harmonic impedance calculations. Final report  

SciTech Connect

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.

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

29

Finite element calculation of harmonic losses in AC machine windings  

Microsoft Academic Search

The finite-element method (FEM) with circuit constraints is used to study the problem of harmonic losses in stranded conductors typically found in AC machines. A discussion of the method is given along with examples using actual motor windings. The results of the finite element calculations are compared to a closed-form solution which ignores the effects of eddy currents on the

S. J. Salon; L. Ovacik; J. F. Balley

1993-01-01

30

Calculation of spin resonance harmonics in an accelerator with Snakes  

NASA Astrophysics Data System (ADS)

In this work, the ASPIRRIN code has been extended to provide the calculation of resonance harmonics for the case of machine with Siberian Snakes and spin rotators. Examples are shown for RHIC accelerator, including the case of the configuration with six Snakes per RHIC ring.

Ptitsyn, V.; Khalil, N.

2014-01-01

31

High-order harmonic transient grating spectroscopy of SF6 molecular vibrations  

NASA Astrophysics Data System (ADS)

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.

Ferré, Amélie; Staedter, David; Burgy, Frédéric; Dagan, Michal; Descamps, Dominique; Dudovich, Nirit; Petit, Stéphane; Soifer, Hadas; Blanchet, Valérie; Mairesse, Yann

2014-06-01

32

Application of higher harmonic blade feathering on the OH-6A helicopter for vibration reduction  

NASA Technical Reports Server (NTRS)

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.

Straub, F. K.; Byrns, E. V., Jr.

1986-01-01

33

Anharmonic calculation of the structure, vibrational frequencies and intensities of the NH3···trans-HONO complex.  

PubMed

The equilibrium geometry of the NH3···trans-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 Schrödinger 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 NH3···trans-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

Bulychev, Valentin P; Buturlimova, Marina V; Tokhadze, Konstantin G

2013-09-19

34

Selected new developments in vibrational structure theory: potential construction and vibrational wave function calculations.  

PubMed

This perspective addresses selected recent developments in the theoretical calculation of vibrational spectra, energies, wave functions and properties. The theoretical foundation and recently developed computational protocols for constructing hierarchies of vibrational Hamiltonian operators are reviewed. A many-mode second quantization (SQ) formulation is discussed prior to the discussion of anharmonic wave functions. Emphasis is put on vibrational self-consistent field (VSCF) based methods and in particular vibrational coupled cluster (VCC) theory. Other issues are also reviewed briefly, such as inclusion of thermal effects, response theoretical calculation of spectra, and the difficulty in treating dense spectra. PMID:22491444

Christiansen, Ove

2012-04-10

35

Efficient calculation of anharmonic vibrational spectra of large molecules with localized modes.  

PubMed

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

Panek, Pawe? T; Jacob, Christoph R

2014-10-20

36

Multi-harmonic measurements and numerical simulations of nonlinear vibrations of a beam with non-ideal boundary  

E-print Network

Multi-harmonic measurements and numerical simulations of nonlinear vibrations of a beam with non-clamped steel beam with non-ideal boundary conditions. A multi-harmonic comparison of simulations of the model. Then, two numerical methods, the Harmonic Balance Method and a time-integration method

Boyer, Edmond

37

Experimental Analysis of a Piezoelectric Energy Harvesting System for Harmonic, Random, and Sine on Random Vibration  

SciTech Connect

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.

Cryns, Jackson W.; Hatchell, Brian K.; Santiago-Rojas, Emiliano; Silvers, Kurt L.

2013-07-01

38

Harmonic analysis of a magnetorheological damper for vibration control  

Microsoft Academic Search

Semi-active control systems are becoming more popular because they offer both the reliability of passive systems and the versatility of active control systems without imposing heavy power demands. In particular, it has been found that magnetorheological (MR) fluids can be designed to be very effective vibration control actuators, which use MR fluids to produce controllable damping force. The objective of

W H Liao; C Y Lai

2002-01-01

39

Dynamic (hyper)polarizabilities of the ozone molecule: Coupled cluster calculations including vibrational corrections  

NASA Astrophysics Data System (ADS)

In this work, we present results for dynamical (hyper)polarizabilities of the ozone molecule with inclusion of vibrational corrections. Electronic contributions for dynamic properties were computed analytically at the single and double coupled cluster level through response theories for the frequencies 0, 0.0239, 0.0428, and 0.0656 hartree. In the static limit, the electronic contributions were also computed at the single and double coupled cluster with perturbative correction of connected triple excitations level by means of the finite-field method. It was found that the inclusion of connected triple excitations is important, especially for a reliable description of the hyperpolarizabilities. Vibrational corrections were calculated by means of the perturbation theoretical method. The zero-point vibrational average correction was found to be relevant only for the linear polarizability, representing approximately 8% of the corresponding electronic contribution. Results also showed that the pure vibrational correction is relevant for the dc-Pockels effect, dc-second harmonic generation, intensity dependent refractive index, and dc-Kerr effect nonlinear optical processes. The double-harmonic approximation is in general suitable to compute this correction, the anharmonicity being small for the dc-Kerr effect and negligible for the other processes.

Naves, Emílio S.; Castro, Marcos A.; Fonseca, Tertius L.

2011-02-01

40

Molecular structure, vibrational spectra and DFT molecular orbital calculations (TD-DFT and NMR) of the antiproliferative drug Methotrexate  

NASA Astrophysics Data System (ADS)

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.

Ayyappan, S.; Sundaraganesan, N.; Aroulmoji, V.; Murano, E.; Sebastian, S.

2010-09-01

41

Multi-channel electronic and vibrational dynamics in polyatomic resonant high-order harmonic generation.  

PubMed

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

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

42

Multi-channel electronic and vibrational dynamics in polyatomic resonant high-order harmonic generation  

NASA Astrophysics Data System (ADS)

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.

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

43

Higher harmonic control analysis for vibration reduction of helicopter rotor systems  

NASA Technical Reports Server (NTRS)

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.

Nguyen, Khanh Q.

1994-01-01

44

Calculation of vibration reduction design for underground sources  

NASA Astrophysics Data System (ADS)

The problems of ecology situation control near intensive underground acoustical sources is considered. Studied vibration absorbers are modeled by multi-component system of connected oscillators with damping. Obtained oscillatory equation system was investigated numerically. Frequency dependencies of absorbers efficiency have been calculated. An influence of the physical-mechanical parameters of the surrounding ground on the value of vibration reduction has been determined. Some variants of principal realization of vibration absorbers for the case of underground railway are discussed. [Work supported by Russian Foundation for Basic Researches Grants Nos. 01-02-16127, 02-02-17143.

Kostarev, Stanislav A.; Rybak, Samuil A.; Makhortykh, Sergey A.

2003-10-01

45

Ab initio calculation of the rotational spectrum of methane vibrational ground state.  

PubMed

In a previous article we have introduced an alternative perturbation scheme to the traditional one starting from the harmonic oscillator, rigid rotator Hamiltonian, to find approximate solutions of the spectral problem for rotation-vibration molecular Hamiltonians. The convergence of our method for the methane vibrational ground state rotational energy levels was quicker than that of the traditional method, as expected, and our predictions were quantitative. In this second article, we study the convergence of the ab initio calculation of effective dipole moments for methane within the same theoretical frame. The first order of perturbation when applied to the electric dipole moment operator of a spherical top gives the expression used in previous spectroscopic studies. Higher orders of perturbation give corrections corresponding to higher centrifugal distortion contributions and are calculated accurately for the first time. Two potential energy surfaces of the literature have been used for solving the anharmonic vibrational problem by means of the vibrational mean field configuration interaction approach. Two corresponding dipole moment surfaces were calculated in this work at a high level of theory. The predicted intensities agree better with recent experimental values than their empirical fit. This suggests that our ab initio dipole moment surface and effective dipole moment operator are both highly accurate. PMID:22583232

Cassam-Chenaï, P; Liévin, J

2012-05-01

46

Vibronic-structure tracking: A shortcut for vibrationally resolved UV/Vis-spectra calculations  

NASA Astrophysics Data System (ADS)

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.

Barton, Dennis; König, Carolin; Neugebauer, Johannes

2014-10-01

47

Vibrational spectra and density functional theoretical calculations on the anti-neurodegenerative drug: Orphenadrine hydrochloride  

NASA Astrophysics Data System (ADS)

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.

Edwin, Bismi; Hubert Joe, I.

2012-11-01

48

A Harmonic Approach for Calculating Daily Temperature Normals Constrained by2 Homogenized Monthly Temperature Normals3  

E-print Network

1 1 A Harmonic Approach for Calculating Daily Temperature Normals Constrained by2 Homogenized a constrained harmonic technique that forces the daily30 temperature normals to be consistent with the monthly, or harmonic even though the annual march of temperatures for some locations can be highly asymmetric. Here, we

49

Vibrational spectroscopic studies of Isoleucine by quantum chemical calculations.  

PubMed

In this work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of Isoleucine (2-Amino-3-methylpentanoic acid). The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments, thermodynamics properties, NBO analyses, NMR chemical shifts and ultraviolet-visible spectral interpretation of Isoleucine have been studied by performing MP2 and DFT/cc-pVDZ level of theory. The FTIR, FT-Raman spectra were recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1) respectively. The UV-visible absorption spectra of the compound were recorded in the range of 200-800 nm. Computational calculations at MP2 and B3LYP level with basis set of cc-pVDZ is employed in complete assignments of Isoleucine molecule on the basis of the potential energy distribution (PED) of the vibrational modes, calculated using VEDA-4 program. The calculated wavenumbers are compared with the experimental values. The difference between the observed and calculated wavenumber values of most of the fundamentals is very small. (13)C and (1)H nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method and compared with experimental results. The formation of hydrogen bond was investigated in terms of the charge density by the NBO calculations. Based on the UV spectra and TD-DFT calculations, the electronic structure and the assignments of the absorption bands were carried out. Besides, molecular electrostatic potential (MEP) were investigated using theoretical calculations. PMID:24508874

Moorthi, P P; Gunasekaran, S; Ramkumaar, G R

2014-04-24

50

Anharmonic vibrational analysis of 3,4-diaminopyridine and 3-aminopyridine by density functional theory calculations.  

PubMed

In this work, we will report a combined experimental and theoretical study on molecular structure and vibrational analysis of 3,4-diaminopyridine (3,4-DAP) and 3-aminopyridine (3-AP). The Fourier transform infrared and Fourier transform Raman spectra of 3,4-DAP were recorded in the solid phase. The molecular geometry, harmonic vibrational wavenumbers of 3-AP and 3,4-DAP in the ground-state have been calculated by using MP2 and density functional methods (B3LYP) using 6-311++G(d,p) as basis set. Predicted electronic absorption spectra 3,4-DAP from TD-DFT calculation have been analyzed comparing with the experimental UV-vis spectrum. The calculated HOMO and LUMO energies show that charge transfer occur in the molecule. A detailed interpretation of the infrared spectra of 3-AP and 3,4-DAP is reported. The theoretical spectrograms for FTIR and FT-Raman spectra of the title molecules have also been constructed. Comparison of the experimental spectra with anharmonic vibrational wavenumbers indicates that B3LYP results are more accurate. PMID:20483656

Karpagam, J; Sundaraganesan, N; Kalaichelvan, S; Sebastian, S

2010-09-01

51

Calculation of the vibrational frequencies of carbon clusters and fullerenes with empirical potentials.  

PubMed

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

Do, Hainam; Besley, Nicholas A

2015-02-01

52

Improved Calculation of Vibrational Mode Lifetimes in Anharmonic Solids  

NASA Astrophysics Data System (ADS)

We propose and evaluate a formal foundation for practical calculations of vibrational mode lifetimes in solids. The approach is based on a recursion method analysis of the Liouvillian. From this we derive the lifetime of a vibrational mode in terms of moments of the power spectrum of the Liouvillian as projected onto the relevant subspace of phase space. In practical terms, the moments are evaluated as ensemble averages of well-defined operators, meaning that the entire calculation is to be done with Monte Carlo. These insights should lead to significantly shorter calculations and improved understanding of mode lifetimes and lattice thermal conductivity. Evaluation performed on model systems have been encouraging. [See Dickel & Daw, Comp Mat Sci, v47 p698 and v49 p445 (2010)].

Daw, Murray; Gao, Yang; Dickel, Doyl; Harrison, David

2013-03-01

53

Investigating the calculation of anharmonic vibrational frequencies using force fields derived from density functional theory.  

PubMed

The calculation of anharmonic vibrational frequencies for a set of small molecules has been examined to explore the merit of applying such computationally expensive approaches for large molecules with density functional theory. The performance of different hybrid and gradient-corrected exchange-correlation functionals has been assessed for the calculation of anharmonic vibrational frequencies using second-order vibrational perturbation theory with two- and four-mode couplings and compared to the recently developed transition optimized shifted Hermite method. A range of exchange-correlation functionals (B3LYP, BLYP, EDF1, EDF2, B97-1, B97-2, HCTH-93, HCTH-120, HCTH-147, and HCTH-407) have been evaluated with reference to a large experimental data set comprising 88 species and 655 modes as well as a smaller set of shifts in frequency because of anharmonicity derived from experimental data. The anharmonic frequencies calculated using hybrid functionals provide the best agreement with experiment, and are not significantly improved by frequency scaling factors, indicating an absence of significant systematic error. For the molecules studied, the B97-1 and B97-2 functionals give the closest overall agreement with experiment, although the improvement over the best case for pure harmonic frequencies is modest. Predictions of the experimental anharmonic shifts are closest for the B3LYP and EDF2 functionals, with B97-1 performing well because of a good description of the harmonic force field. Investigations using modified hybrid functionals with increased fractions of Hartree-Fock exchange indicate that approximately 20% Hartree-Fock exchange is optimal. PMID:22483009

Hanson-Heine, Magnus W D; George, Michael W; Besley, Nicholas A

2012-05-01

54

Calculation of mechanical vibration frequencies of stiffened superconducting cavities  

SciTech Connect

We calculated the frequencies of transverse and longitudinal mechanical-vibration modes of the HEPL- modified, CERN/DESY four-cell superconducting cavity, using finite-element techniques. We compared the results of these calculations, including the stiffening of the cavity with rods, with mode frequencies measured at HEPL. The correlation between data was significant. The same techniques were also used to design and optimize the stiffening scheme for the seven-cell 805-MHz superconducting cavity being developed at Los Alamos. In this report, we describe the final stiffening scheme and the results of our calculations.

Black, S.J.; Spalek, G.

1992-01-01

55

Calculation of mechanical vibration frequencies of stiffened superconducting cavities  

SciTech Connect

We calculated the frequencies of transverse and longitudinal mechanical-vibration modes of the HEPL- modified, CERN/DESY four-cell superconducting cavity, using finite-element techniques. We compared the results of these calculations, including the stiffening of the cavity with rods, with mode frequencies measured at HEPL. The correlation between data was significant. The same techniques were also used to design and optimize the stiffening scheme for the seven-cell 805-MHz superconducting cavity being developed at Los Alamos. In this report, we describe the final stiffening scheme and the results of our calculations.

Black, S.J.; Spalek, G.

1992-09-01

56

Vibration analysis of cracked rotor sliding bearing system with rotor-stator rubbing by harmonic wavelet transform  

NASA Astrophysics Data System (ADS)

In this paper, the vibration of a cracked rotor sliding bearing system with rotor-stator rubbing is investigated using harmonic wavelet transform (HWT). Three non-linear factors, non-linear oil film forces, rotor-stator rubbing and the presence of crack, are taken into account. So the non-linear behavior of the rotor will be much more complex. According to Newmark method, the dynamic response of the rotor is calculated. Using HWT method, the effect of these non-linear factors is analyzed simultaneously in both time and frequency domain. The numerical simulated result shows that HWT will be available to analyze this multi-non-linear factors rotor effectively and can reveal the exact fault characteristics in detail.

Wan, Fangyi; Xu, Qingyu; Li, Songtao

2004-04-01

57

Computing multiple periodic solutions of nonlinear vibration problems using the harmonic balance method and Groebner bases  

NASA Astrophysics Data System (ADS)

This paper is devoted to the study of vibration of mechanical systems with geometric nonlinearities. The harmonic balance method is used to derive systems of polynomial equations whose solutions give the frequency component of the possible steady states. Groebner basis methods are used for computing all solutions of polynomial systems. This approach allows to reduce the complete system to an unique polynomial equation in one variable driving all solutions of the problem. In addition, in order to decrease the number of variables, we propose to first work on the undamped system, and recover solution of the damped system using a continuation on the damping parameter. The search for multiple solutions is illustrated on a simple system, where the influence of the retained number of harmonic is studied. Finally, the procedure is applied on a simple cyclic system and we give a representation of the multiple states versus frequency.

Grolet, Aurelien; Thouverez, Fabrice

2015-02-01

58

Molecular structure and vibrational spectroscopic investigation of melamine using DFT theory calculations.  

PubMed

The FT-Raman and FT-IR spectra for melamine have been recorded in the region 4000-100cm(-1) and 4000-400cm(-1), respectively compared with the harmonic vibrational frequencies calculated using density functional theory method (B3LYP) by employing 6-31G(d,p) and 6-311++G(d,p) basis set with appropriate scaling factors. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values. The experimental geometrical parameters prove satisfactory concurrence with the theoretical prediction from DFT. The scaled vibrational frequencies seem to coincide with the experimentally observed values with acceptable deviations. The theoretical spectrograms have been constructed and compared with the experimental FT-Raman and FT-IR spectra. The calculated Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energies show that charge transfer occurs in the molecule. The first order hyperpolarizability ?total of this molecular system and related properties (?, ?, ? and ??) are calculated using DFT/B3LYP/6-31G(d,p) and 6-311++G(d,p) basis set based on the finite-field approach. Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Thermodynamic properties like entropy, heat capacity and zero-point energy have been calculated for the molecule. PMID:24412793

Prabhaharan, M; Prabakaran, A R; Gunasekaran, S; Srinivasan, S

2014-04-01

59

Experimental, theoretical calculations of the vibrational spectra and conformational analysis of 2,4-di-tert-butylphenol.  

PubMed

In the present work, we reported a combined experimental and theoretical study on conformational stability, molecular structure and vibrational spectra of 2,4-di-tert-butylphenol (2,4-DTBP). The FT-IR (400-4000cm(-1)) and FT-Raman spectra (50-3500cm(-1)) of 2,4-DTBP were recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of 2,4-DTBP in the ground-state have been calculated by using the density functional BLYP/B3LYP methods. The energy calculated by time-dependent density functional theory (TD-DFT) result complements with the experimental findings. The calculated highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies show that charge transfer occurs within the molecule. Finally the calculation results were compared with measured infrared and Raman spectra of the title compound which showed good agreement with observed spectra. PMID:22020168

Kalaichelvan, S; Sundaraganesan, N; Dereli, O; Sayin, U

2012-01-01

60

Multi-harmonic measurements and numerical simulations of nonlinear vibrations of a beam with non-ideal boundary conditions  

NASA Astrophysics Data System (ADS)

This study presents a direct comparison of measured and predicted nonlinear vibrations of a clamped-clamped steel beam with non-ideal boundary conditions. A multi-harmonic comparison of simulations with measurements is performed in the vicinity of the primary resonance. First of all, a nonlinear analytical model of the beam is developed taking into account non-ideal boundary conditions. Three simulation methods are implemented to investigate the nonlinear behavior of the clamped-clamped beam. The method of multiple scales is used to compute an analytical expression of the frequency response which enables an easy updating of the model. Then, two numerical methods, the Harmonic Balance Method and a time-integration method with shooting algorithm, are employed and compared one with each other. The Harmonic Balance Method enables to simulate the vibrational stationary response of a nonlinear system projected on several harmonics. This study then proposes a method to compare numerical simulations with measurements of all these harmonics. A signal analysis tool is developed to extract the system harmonics' frequency responses from the temporal signal of a swept sine experiment. An evolutionary updating algorithm (Covariance Matrix Adaptation Evolution Strategy), coupled with highly selective filters is used to identify both fundamental frequency and harmonic amplitudes in the temporal signal, at every moment. This tool enables to extract the harmonic amplitudes of the output signal as well as the input signal. The input of the Harmonic Balance Method can then be either an ideal mono-harmonic signal or a multi-harmonic experimental signal. Finally, the present work focuses on the comparison of experimental and simulated results. From experimental output harmonics and numerical simulations, it is shown that it is possible to distinguish the nonlinearities of the clamped-clamped beam and the effect of the non-ideal input signal.

Claeys, M.; Sinou, J.-J.; Lambelin, J.-P.; Alcoverro, B.

2014-12-01

61

Vibrational spectra of berberine and their interpretation by means of DFT quantum-mechanical calculations  

E-print Network

Experimental vibrational spectra (Raman and infrared absorption) of berberine are obtained at room temperature. The vibrational spectra of berberine are calculated by the DFT method at the B3LYP/6-311++G(d,p) level. Based on the correlation between experimental and calculated data, the vibrational spectrum is interpreted in the frequency range of 800-1700 cm-1 in detail. The experimental and calculated spectra of intramolecular vibrations are found to correlate closely

Bashmakova, N; Zhurakivsky, R; Hovorun, D; Yashchuk, V

2011-01-01

62

On the effect of acoustic coupling on random and harmonic plate vibrations  

NASA Technical Reports Server (NTRS)

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.

Frendi, A.; Robinson, J. H.

1993-01-01

63

Mapping quadrupole collectivity in the Cd isotopes: The breakdown of harmonic vibrational motion  

NASA Astrophysics Data System (ADS)

The stable Cd isotopes have long been used as paradigms for spherical vibrational motion. Extensive investigations with in-beam ? spectroscopy have resulted in very-well-established level schemes, including many lifetimes or lifetime limits. A programme has been initiated to complement these studies with very-high-statistics ? decay using the 8? spectrometer at the TRIUMF radioactive beam facility. The decays of 112In and 112Ag have been studied with an emphasis on the observation of, or the placement of stringent limits on, low-energy branches between potential multi-phonon levels. A lack of suitable 0+ or 2+ three-phonon candidates has been revealed. Further, the sum of the B(E2) strength from spin 0+ and 2+ states up to 3 MeV in excitation energy to the assigned two-phonon levels falls far short of the harmonic-vibrational expectations. This lack of strength points to the failing of collective models based on vibrational phonon structures.

Garrett, P. E.; Green, K. L.; Bangay, J.; Varela, A. Diaz; Sumithrarachchi, C. S.; Austin, R. A. E.; Ball, G. C.; Bandyopadhyay, D. S.; Bianco, L.; Colosimo, S.; Cross, D. S.; Demand, G. A.; Finlay, P.; Garnsworthy, A. B.; Grinyer, G. F.; Hackman, G.; Kulp, W. D.; Leach, K. G.; Morton, A. C.; Orce, J. N.; Pearson, C. J.; Phillips, A. A.; Schumaker, M. A.; Svensson, C. E.; Triambak, S.; Wong, J.; Wood, J. L.; Yates, S. W.

2011-10-01

64

An analytical derivative procedure for the calculation of vibrational Raman optical activity spectra.  

PubMed

We present an analytical time-dependent Hartree-Fock algorithm for the calculation of the derivatives of the electric dipole-magnetic dipole polarizability with respect to atomic Cartesian coordinates. Combined with analogous procedures to determine the derivatives of the electric dipole-electric dipole and electric dipole-electric quadrupole polarizabilities, it enables a fully analytical evaluation of the three frequency-dependent vibrational Raman optical activity (VROA) invariants within the harmonic approximation. The procedure employs traditional non-London atomic orbitals, and the gauge-origin dependence of the VROA intensities has, therefore, been assessed for the commonly used aug-cc-pVDZ and rDPS:3-21G basis sets. PMID:18052417

Liégeois, Vincent; Ruud, Kenneth; Champagne, Benoît

2007-11-28

65

Vibrationally excited states of HC5N: millimeter-wave spectroscopy and coupled cluster calculations  

NASA Astrophysics Data System (ADS)

The rotational spectrum of HC5N has been investigated in the millimeter-wave region, from 60 to 290 GHz, for 15 vibrationally excited states which lie approximately between 500 and 860 cm-1, namely (v6v7v8v9v10v11) = (000005), (000006), (000007), (000008), (000020), (000030), (001000), (010000), (100000), (000021), (000101), (001001), (010001), (000110), and (001010). Gas-phase copyrolysis of pyridine and phosphorus trichloride or, alternatively, a dc discharge in a gaseous mixture of vinyl cyanide and acetylene were used to produce the semi-stable HC5N molecule. A large number of vibrational and rovibrational interactions has been taken into account to fit properly the measured transition frequencies of the states investigated. The most important perturbations are caused by the high-order Coriolis resonances observed between the (v8, v10) and (v8 - 1, v10 + 2) states, and between the (v7, v10, v11) and (v7 - 1, v10 + 3, v11 - 1) states, and by the cubic anharmonic interactions which mix the (v6, v8, v11) states with the (v6 - 1, v8 + 1, v11 + 1) states, and the (v6, v10) states with the (v6 - 1, v10 + 2) states. The analysis of the spectra was facilitated by CCSD(T) calculations with the cc-pVQZ basis, which provided accurate predictions of a large variety of spectroscopic constants like harmonic vibrational wavenumbers, vibration rotation coupling constants, l-type doubling constants, and normal-coordinate cubic force constants. Excellent agreement between experiment and theory was generally observed, even when the experimental data were strongly perturbed by resonance effects.

Degli Esposti, C.; Bizzocchi, L.; Botschwina, P.; Yamada, K. M. T.; Winnewisser, G.; Thorwirth, S.; Förster, P.

2005-04-01

66

Automated calculation of anharmonic vibrational contributions to first hyperpolarizabilities: quadratic response functions from vibrational configuration interaction wave functions.  

PubMed

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, H(2)O, CH(2)O, 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. PMID:20568841

Hansen, Mikkel Bo; Christiansen, Ove; Hättig, Christof

2009-10-21

67

Calculations of vibration-rotation energy levels of HD+  

NASA Astrophysics Data System (ADS)

An artificial-channels scattering method [M. Shapiro and G. G. Balint-Kurti, J. Chem. Phys. 71, 1461 (1979)] is used with a transformed Hamiltonian [R. E. Moss and I. A. Sadler, Molec. Phys. 66, 591 (1989)] to calculate the energies of vibration-rotation levels for the ground electronic state of HD+. All nonadiabatic effects, except for part of the coupling of rotational and electronic angular momenta, are accounted for. The results, which are for v=0-21, J=0,1, together with some other levels involved in observed transitions, are compared with previous calculations, particularly those of Wolniewicz and Poll [Molec. Phys. 59, 953 (1986)]. Inclusion of a correction to the energies of J?0 levels to allow for the remaining contribution of ? electronic states permits comparison with experimental transition energies. The agreement is excellent.

Balint-Kurti, G. G.; Moss, R. E.; Sadler, I. A.; Shapiro, M.

1990-05-01

68

PHYSICAL REVIEW A 90, 063412 (2014) Effect of nuclear vibration on high-order-harmonic generation of aligned H2  

E-print Network

PHYSICAL REVIEW A 90, 063412 (2014) Effect of nuclear vibration on high-order-harmonic generation of aligned H2 + molecules Dmitry A. Telnov,1,* John Heslar,2, and Shih-I Chu2,3, 1 Department of Physics, St. Petersburg State University, St. Petersburg 198504, Russia 2 Department of Physics, Center for Quantum

Chu, Shih-I

69

A simplified approach for the calculation of acoustic emission in the case of friction-induced noise and vibration  

NASA Astrophysics Data System (ADS)

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.

Soobbarayen, K.; Besset, S.; Sinou, J.-. J.

2015-01-01

70

Harmonic vibrations and thermodynamic stability of a DNA oligomer in monovalent salt solution.  

PubMed Central

We compute the full harmonic vibrational spectrum and eigenmodes of a DNA oligomer, d(C-G)3, in optimized B and Z conformations in various ionic environments (0.01-5.0 M NaCl). The statistical interactions of DNA with the diffuse ionic cloud surrounding it in solution are approximately represented within the potential of mean force framework. The lowest eigenfrequency of the B conformation is found to drastically decrease with increased NaCl concentration. This suggests that a soft mode mechanism may be a precursor for the B-to-Z conversion. The free energy balance governing the B-Z isomerization of d(C-G)3 is dominated by the solvent-averaged effective phosphate-phosphate interactions due to substantial cancelations between the much larger intramolecular energy contributions. PMID:2717613

García, A E; Soumpasis, D M

1989-01-01

71

Vibrational subsystem analysis: A method for probing free energies and correlations in the harmonic limit  

PubMed Central

A new vibrational subsystem analysis (VSA) method is presented for coupling global motion to a local subsystem while including the inertial effects of the environment. The premise of the VSA method is a partitioning of a system into a smaller region of interest and a usually larger part referred to as environment. This method allows the investigation of local-global coupling, a more accurate estimation of vibrational free energy contribution for parts of a large system, and the elimination of the “tip effect” in elastic network model calculations. Additionally, the VSA method can be used as a probe of specific degrees of freedom that may contribute to free energy differences. The VSA approach can be employed in many ways, but it will likely be most useful for estimating activation free energies in QM?MM reaction path calculations. Four examples are presented to demonstrate the utility of this method. PMID:19063546

Woodcock, H. Lee; Zheng, Wenjun; Ghysels, An; Shao, Yihan; Kong, Jing; Brooks, Bernard R.

2008-01-01

72

Optimal semi-active vibration absorber for harmonic excitation based on controlled semi-active damper  

NASA Astrophysics Data System (ADS)

The semi-active vibration absorber (SVA) based on controlled semi-active damper is formulated to realize the behaviour of the passive undamped vibration absorber tuned to the actual harmonic disturbing frequency. It is shown that the controlled stiffness force, which is emulated by the semi-active damper to realize the precise real-time frequency tuning of the SVA, is unpreventably combined with the generation of undesirable damping in the semi-active damper whereby the SVA does not behave as targeted. The semi-active stiffness force is therefore optimized for minimum primary structure response. The results point out that the optimal semi-active stiffness force reduces the undesirable energy dissipation in the SVA at the expenses of slight imprecise frequency tuning. Based on these findings, a real-time applicable suboptimal SVA is formulated that also takes the relative motion constraint of real mass dampers into account. The results demonstrate that the performance of the suboptimal SVA is closer to that of the active solution than that of the passive mass damper.

Weber, F.

2014-09-01

73

Vibrational spectra, quantum chemical calculations and spectral assignments of 1,1-difluoro-1-silacyclohexane  

NASA Astrophysics Data System (ADS)

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.

Guirgis, Gamil A.; Dukes, Horace W.; Wyatt, Justin K.; Nielsen, Claus J.; Horn, Anne; Aleksa, Valdemaras; Klaeboe, Peter

2015-02-01

74

Conformational stability, r0 structural parameters, vibrational assignments and ab initio calculations of ethyldichlorophosphine  

NASA Astrophysics Data System (ADS)

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 88 ± 9 cm-1 (1.04 ± 0.11 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.

Darkhalil, Ikhlas D.; Paquet, Charles; Waqas, Mohammad; Gounev, Todor K.; Durig, James R.

2015-02-01

75

Conformational stability, r0 structural parameters, vibrational assignments and ab initio calculations of ethyldichlorophosphine.  

PubMed

Variable temperature (-60 to -100°C) studies of ethyldichlorophosphine, CH3CH2PCl2, of the infrared spectra (4000-400cm(-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 88±9cm(-1) (1.04±0.11kJ/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

Darkhalil, Ikhlas D; Paquet, Charles; Waqas, Mohammad; Gounev, Todor K; Durig, James R

2015-02-01

76

Vibrational spectra, quantum chemical calculations and spectral assignments of 1,1-difluoro-1-silacyclohexane.  

PubMed

Raman spectra of 1,1-difluoro-1-silacyclohexane as a liquid, and as a solid at 78K 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 15kJmol(-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

Guirgis, Gamil A; Dukes, Horace W; Wyatt, Justin K; Nielsen, Claus J; Horn, Anne; Aleksa, Valdemaras; Klaeboe, Peter

2015-02-01

77

Comparative Study on Calculation Methods of Blasting Vibration Velocity  

NASA Astrophysics Data System (ADS)

Due to the extreme complexities in rock blasting and difficulties in theoretical or numerical analysis, and the enormous consumption of explosives in mining and construction operations, empirical or semi-empirical formulae for blasting vibration velocity (BVV) were obtained from observations and measurements in field blast tests and are still widely used all over the world. This paper investigates the fitting degree and characteristics of several calculation methods for BVV based on 34 sets of data samples from 27 projects belonging to 4 types. The results indicate that both the cube-root scaling formula and the square-root scaling formula have relatively good fitting degree, while the multiple regression analysis can give the best fitting outcome if the sample space satisfies certain requirements. Whether the cube-root scaling formula or the square-root scaling formula is chosen to analyze the relationship between BVV and scaled distance depends on the average scaled distance under cubic-root scaling. If the average scaled distance is over 0.1, the cube-root scaling formula should be used; otherwise, the square-root scaling formula should be used. Bigger samples integrated from data samples of different projects but in the same type were then analyzed to get the empirical relations for different types of projects. The correlation coefficients of these relations are quite good, thus these relations can be used for reference in other similar projects. This paper then discusses the physical meanings of parameters in different formulae, sample selection and parameter choice for BVV. It suggests that the current calculation methods for explosive charge, blasting-to-monitoring distance and scaled distance need to be improved. It also concludes that the integrated BVV from velocity components in three-dimensions is more reasonable on a theoretical basis. It can yield good results in predicting the blasting vibration, and should be used as widely as possible.

Liang, Qingguo; An, Yafang; Zhao, Lei; Li, Dewu; Yan, Liping

2011-01-01

78

Converged vibrational energy levels and quantum mechanical vibrational partition function of ethane  

E-print Network

Converged vibrational energy levels and quantum mechanical vibrational partition function of ethane-0431 Received 25 January 2006; accepted 15 March 2006; published online 9 May 2006 The vibrational partition that were calculated by vibrational configuration interaction, and the results are compared to the harmonic

Truhlar, Donald G

79

Molecular structure and vibrational study of diprotonated guanazolium using DFT calculations and FT-IR and FT-Raman spectroscopies.  

PubMed

The purpose of this manuscript is to discuss our investigations of diprotonated guanazolium chloride using vibrational spectroscopy and quantum chemical methods. The solid phase FT-IR and FT-Raman spectra were recorded in the regions 4000-400cm(-1) and 3600-50cm(-1) respectively, and the band assignments were supported by deuteration effects. Different sites of diprotonation have been theoretically examined at the B3LYP/6-31G level. The results of energy calculations show that the diprotonation process occurs with the two pyridine-like nitrogen N2 and N4 of the triazole ring. The molecular structure, harmonic vibrational wave numbers, infrared intensities and Raman activities were calculated for this form by DFT/B3LYP methods, using a 6-31G basis set. Both the optimized geometries and the theoretical and experimental spectra for diprotonated guanazolium under a stable form are compared with theoretical and experimental data of the neutral molecule reported in our previous work. This comparison reveals that the diprotonation occurs on the triazolic nucleus, and provide information about the hydrogen bonding in the crystal. The scaled vibrational wave number values of the diprotonated form are in close agreement with the experimental data. The normal vibrations were characterized in terms of potential energy distribution (PED) using the VEDA 4 program. PMID:22925973

Guennoun, L; Zaydoun, S; El Jastimi, J; Marakchi, K; Komiha, N; Kabbaj, O K; El Hajji, A; Guédira, F

2012-11-01

80

Extra Low-Frequency Terrestrial Radio-Wave Field Calculations with the Zonal Harmonics Series  

Microsoft Academic Search

Use of the zonal harmonics series for calculating the terrestrial wave guide fields directly is described. The analysis is extended to include radio waves propagating into sea water or below the earth's surface. A sample calculation of ELF radio waves is analyzed into a direct wave and a wave that has traveled the circumference of the earth. The location of

J. Ralph Johler; Richard L. Lewis

1969-01-01

81

Variational Calculations of IR Ro-Vibrational Spectra for Nitric Acid  

NASA Astrophysics Data System (ADS)

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 Schrödinger 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.

Pavlyuchko, A. I.; Yurchenko, S. N.; Tennyson, J.

2013-09-01

82

Spectral Analysis of Vibrational Harmonic Motion by use of a Continuous-Wave CO2 Doppler Lidar  

NASA Technical Reports Server (NTRS)

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.

Jarzembski, Maurice A.; Srivastava, Vandana

1999-01-01

83

Six-Bodies Calculations Using the Hyperspherical Harmonics Method  

NASA Astrophysics Data System (ADS)

In this work we show results for light nuclear systems and small clusters of helium atoms using the hyperspherical harmonics basis. We use the basis without previous symmetrization or antisymmetrization of the state. After the diagonalization of the Hamiltonian matrix, the eigenvectors have well defined symmetry under particle permutation and the identification of the physical states is possible. We show results for systems composed up to six particles. As an example of a fermionic system, we consider a nucleon system interacting through the Volkov potential, used many times in the literature. For the case of bosons, we consider helium atoms interacting through a potential model which does not present a strong repulsion at short distances. We have used an attractive gaussian potential to reproduce the values of the dimer binding energy, the atom-atom scattering length, and the effective range obtained with one of the most widely used He-He interaction, the LM2M2 potential. In addition, we include a repulsive hypercentral three-body force to reproduce the trimer binding energy.

Gattobigio, M.; Kievsky, A.; Viviani, M.

2013-05-01

84

Accurate calculation and assignment of highly excited vibrational levels of floppy triatomic molecules in a basis of adiabatic vibrational eigenstates  

NASA Astrophysics Data System (ADS)

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.

Ba?i?, Z.

1991-09-01

85

Vibrational spectroscopy of protonated imidazole and its complexes with water molecules: ab initio anharmonic calculations and experiments.  

PubMed

The results of anharmonic frequency calculations on neutral imidazole (C3N2H4, Im), protonated imidazole (ImH+), and its complexes with water (ImH+)(H2O)n, are presented and compared to gas phase infrared photodissociation spectroscopy (IRPD) data. Anharmonic frequencies are obtained via ab initio vibrational self-consistent field (VSCF) calculations taking into account pairwise interactions between the normal modes. The key results are: (1) Prediction of anharmonic vibrational frequencies on an MP2 ab initio potential energy surface show excellent agreement with experiment and outstanding improvement over the harmonic frequencies. For example, the ab initio calculated anharmonic frequency for (ImH+)(H2O)N2 exhibits an overall average percentage error of 0.6% from experiment. (2) Anharmonic vibrational frequencies calculated on a semiempirical potential energy surface fitted to ab initio harmonic data represents spectroscopy well, particularly for water complexes. As an example, anharmonic frequencies for (ImH+)H2O and (ImH+)(H2O)2 show an overall average deviation of 1.02% and 1.05% from experiment, respectively. This agreement between theory and experiment also supports the validity and use of the pairwise approximation used in the calculations. (3) Anharmonic coupling due to hydration effects is found to significantly reduce the vibrational frequencies for the NH stretch modes. The frequency of the NH stretch is observed to increase with the removal of a water molecule or replacement of water with N2. This result also indicates the ability of the VSCF method to predict accurate frequencies in a matrix environment. The calculation provides insights into the nature of anharmonic effects in the potential surface. Analysis of percentage anharmoncity in neutral Im and ImH+ shows a higher percentage anharmonicity in the NH and CH stretch modes of neutral Im. Also, we observe that anharmonicity in the NH stretch modes of ImH+ have some contribution from coupling effects, while that of neutral Im has no contribution whatsoever from mode-mode coupling. It is concluded that the incorporation of anharmonic effects in the calculation brings theory and experiment into much closer agreement for these systems. PMID:17500546

Adesokan, Adeyemi A; Chaban, Galina M; Dopfer, Otto; Gerber, R Benny

2007-08-01

86

Molecular structure, normal coordinate analysis, harmonic vibrational frequencies, NBO, HOMO-LUMO analysis and detonation properties of (S)-2-(2-oxopyrrolidin-1-yl) butanamide by density functional methods  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) computations have become an efficient tool in the prediction of molecular structure, harmonic force fields, vibrational wave numbers as well as the IR and Raman intensities of pharmaceutically important molecule. In this work, we report harmonic vibrational frequencies, molecular structure, NBO and HOMO, LUMO analysis and detonation properties of (S)-2-(2-oxopyrrolidin-1-yl) butanamide. The solid phase FT-IR and FT-Raman spectra of (S)-2-(2-oxopyrrolidin-1-yl) butanamide were recorded in the region 4000-450 cm-1 and 4000-50 cm-1 respectively. Harmonic frequencies of this compound were determined and analyzed by DFT utilizing 6-31G(d,p), 6-31+G(d,p) basis sets. 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 calculated infrared and Raman spectra of the title compounds were also stimulated utilizing the scaled force fields and the computed dipole derivatives for IR intensities and polarizability derivatives for Raman intensities. The change in electron density (ED) in the ?* and ?* antibonding orbital's 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. Heat of formation (HOF) and calculated density were estimated to evaluate detonation properties using Kamlet-Jacobs equations. The linear polarizability (?) and the first order hyperpolarizability (?) values of the investigated molecule have been computed using DFT calculations. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The observed and calculated wave numbers are found to be in good agreement. On the basis of vibrational analyses, the thermodynamic properties of title compound at different temperatures have been calculated.

Renuga, S.; Muthu, S.

2014-01-01

87

A structural and vibrational study on the first condensed borosulfate K5[B(SO4)4] by using the FTIR-Raman spectra and DFT calculations  

NASA Astrophysics Data System (ADS)

The first borosulfate, K5[B(SO4)4] (recently synthesized by Henning A. Höppe, Karolina Kazmierczak, Michael Daub, Katharina Förg, Franziska Fuchs, Harald Hillebrecht, 2012) was characterized by infrared and Raman spectroscopies. Density functional theory (DFT) calculations were used to study the structure and vibrational properties of the compound. Employing the B3P86 and B3LYP levels of theory, the molecular structures of the compound were theoretically determined in gas phase and the harmonic vibrational frequencies were evaluated at the same levels. The calculated harmonic vibrational frequencies for the borosulfate compound are consistent with the experimental IR and Raman spectra. These calculations gave us a precise knowledge of the normal modes of vibration taking into account the type of coordination adopted by sulfate groups of this compound as ligands with C3v and C2v symmetries. A complete assignment of all the observed bands in the IR and Raman spectra for K5[B(SO4)4] was performed. Here, the infrared and Raman spectra of K5[B(SO4)4] were interpreted, discussed and completely assigned. The nature of the Ksbnd O, Ksbnd S, Bsbnd O, and Ssbnd O bonds and the topological properties of the compound were investigated and analyzed by means of Natural Bond Order (NBO) and Bader's Atoms in Molecules theory (AIM), respectively.

Höppe, Henning Alfred; Kazmierczak, Karolina; Romano, Elida; Brandán, Silvia Antonia

2013-04-01

88

Ab initio calculations of anharmonic vibrational spectroscopy for hydrogen fluoride (HF) n ( n=3, 4) and mixed hydrogen fluoride\\/water (HF) n (H 2O) n ( n=1, 2, 4) clusters  

Microsoft Academic Search

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

Galina M Chaban; R. Benny Gerber

2002-01-01

89

Harmonic Vibrational Frequencies:  An Evaluation of Hartree?Fock, Møller?Plesset, Quadratic Configuration Interaction, Density Functional Theory, and Semiempirical Scale Factors  

Microsoft Academic Search

Scaling factors for obtaining fundamental vibrational frequencies, low-frequency vibrations, zero-point vibrational energies (ZPVE), and thermal contributions to enthalpy and entropy from harmonic frequencies determined at 19 levels of theory have been derived through a least-squares approach. Semiempirical methods (AM1 and PM3), conventional uncorrelated and correlated ab initio molecular orbital procedures (Hartree- Fock (HF), Møller-Plesset (MP2), and quadratic configuration interaction including

Anthony P. Scott; Leo Radom

1996-01-01

90

Calculation of the Herman-Wallis effect in ?-? vibrational overtone transitions in a linear molecule: Comparison with HCN experimental results  

NASA Astrophysics Data System (ADS)

The high sensitivity of cavity ring-down spectroscopy has allowed us to observe a few perpendicular vibrational overtone transitions of HCN in the visible. These transitions display a sizable Herman-Wallis effect, that is an asymmetry in the relative intensities of the R and P branch lines. We have developed a theory for the first-order Herman-Wallis effect based upon using variational vibrational wave functions but treating the vibration-rotation interaction by first-order perturbation theory. In the specific case of perpendicular transitions, the first-order effect is dominated by Coriolis mixing of ? and ? overtone states. We used the empirical energy surface by Carter, Mills, and Handy [J. Chem. Phys. 99, 4379 (1993)] restricted to the stretching degrees of freedom. Bending was included by multiplication of these stretching wave functions by harmonic wave functions of the bend. Vibrational transition moments were calculated using a polynomial surface fit to ab initio CCSD(T) dipole moment points by Botschwina et al. [Chem. Phys. 190, 345 (1995) and private communication]. We expected that this treatment would be accurate but the calculated Herman-Wallis effect is about one order of magnitude too large. To gain further insight into the poor agreement between theory and experiment, we have calculated the sensitivity of the Herman-Wallis coefficient and of the transition moment to the dipole and energy surface parameters. From this, it appears that the dipole surface, while producing accurate band intensities, could at the same time be inadequate to account for the Herman-Wallis effect. A similar possibility stands for the energy surface, which however is highly constrained by the requirement to fit the observed band origins.

Romanini, Daniele; Lehmann, Kevin K.

1996-07-01

91

Vibrational multiconfiguration self-consistent field theory: implementation and test calculations.  

PubMed

A state-specific vibrational multiconfiguration self-consistent field (VMCSCF) approach based on a multimode expansion of the potential energy surface is presented for the accurate calculation of anharmonic vibrational spectra. As a special case of this general approach vibrational complete active space self-consistent field calculations will be discussed. The latter method shows better convergence than the general VMCSCF approach and must be considered the preferred choice within the multiconfigurational framework. Benchmark calculations are provided for a small set of test molecules. PMID:20370109

Heislbetz, Sandra; Rauhut, Guntram

2010-03-28

92

Microwave, structural, conformational, vibrational studies and ab initio calculations of isocyanocyclopentane.  

PubMed

The infrared and Raman spectra (3200-50cm(-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 (3200-400cm(-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±10cm(-1) (1.21±0.11kJmol(-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): CN=1.176 (3); C?N=1.432 (3); C?C?,C?'=1.534 (3); C?C?,C?'=1.542 (3); C?C?'=1.554 (3) and angles (°):?C?NC=177.8 (5); ?C?C?N=110.4 (5); [Formula: see text] (5); ?C?C?C?=103.6 (5); [Formula: see text] (5). The results are discussed and compared to the corresponding properties of some related molecules. PMID:24480667

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

93

Isotope effects in hydrogen-bonded complexes. Calculation of geometrical and vibrational characteristics of asymmetric isotopologues of [F(HF)2]-.  

PubMed

The geometrical and vibrational characteristics of isolated H-bonded anionic complexes [FHFDF](-), [FHFTF](-), and [FDFTF](-) are calculated quantum-mechanically. The four-dimensional anharmonic vibrational problems are solved by the variational method using the potential energy and dipole moment surfaces calculated in the MP2/6-311++G(3df,3pd) approximation with the basis set superposition error taken into account. Changes in the bond lengths of molecular fragments LF (L = H, D, T) and in the distances between the F(-) anion and the centers of mass of LF are used as the vibrational coordinates. For each isotopologue, the vibrational energy levels, the transition frequencies and absolute intensities for the H-bond and L-F stretching vibrations are determined. To study the isotope effects on the geometrical parameters, the values of internuclear separations and the asymmetry parameter of the F(-)···L-F bridges, averaged over the ground state and several excited vibrational states, are calculated, as well as their standard deviations. The calculations revealed an extremely strong influence of anharmonic coupling between different vibrations on the absorption intensities and a significant mass-dependence of spectroscopic and structural parameters. The geometry and harmonic frequencies of KH(2)F(3), KD(2)F(3), and KHDF(3) are also calculated at a lower ab initio level. The results obtained for [FHFDF](-), [FHFTF](-), and [FDFTF](-) are compared with the available experimental data and the results of earlier calculations of the symmetric complexes [F(HF)(2)](-), [F(DF)(2)](-), and [F(TF)(2)](-) and complexes containing a positive K-meson. PMID:21695326

Bulychev, V P; Buturlimova, M V; Tokhadze, K G

2011-08-21

94

Structural study and characterization of the dipeptide 2-[[5-amino-5-oxo-2-(phenylmethoxycarbonylamino) pentanoyl] amino] acetic acid by vibrational spectroscopy and DFT calculations  

NASA Astrophysics Data System (ADS)

We have studied 2-[[5-amino-5-oxo-2-(phenylmethoxycarbonylamino) pentanoyl] amino] acetic acid and characterized it by infrared and Raman spectroscopies in the solid phase. The Density Functional Theory (DFT) method and Pople's basis set have been used to study its structure and vibrational properties. These calculations have given us a precise understanding of the normal modes of vibration, taking into account the neutral and zwitterionic forms of the compound. The harmonic vibrational wavenumbers for the optimized geometries of both structures were calculated at the B3LYP/6-31G*and B3LYP/6-311G** levels for an isolated molecule. For a complete assignment of the vibrational spectra, DFT calculations were combined with Pulaýs Scaled Quantum Mechanics Force Field (SQMFF) methodology to fit the theoretical and experimental wavenumber values. In this context, an assignment of the observed spectral features is proposed. Four intense bands in the infrared spectrum at 3332, 1734, 1654 and 1534 cm-1 and three bands in the Raman spectrum at 3332, 2928 and 985 cm-1 are reported to characterize both forms of the compound. The theoretical vibrational calculations allowed us to obtain a set of scaled force constants. A Natural Bond Orbital (NBO) study revealed the characteristics of the electronic delocalization of both structures, while the corresponding topological properties of electronic charge density were analyzed by employing Bader's Atoms in the Molecules theory (AIM).

Leyton, Patricio; Paipa, Carolina; Berrios, Andrés; Zárate, Antonio; Castillo, María Victoria; Brandán, Silvia Antonia

2013-01-01

95

A hybrid variational-perturbation calculation of the ro-vibrational spectrum of nitric acid  

E-print Network

Rotation-vibration spectra of the nitric acid molecule, HNO\\3, are calculated for wavenumbers up to 7000~\\cm. Calculations are performed using a Hamiltonian expressed in internal curvilinear vibrational coordinates solved using a hybrid variational-perturbation method. An initial potential energy surface (PES) and dipole moment function (DMF) are calculated {\\it ab initio} at the CCSD(T)/aug-cc-pVQZ level of theory. Parameters of the PES and DMF are varied to minimize differences between the calculated and experimental transition frequencies and intensities. The average, absolute deviation between calculated and experimental values is 0.2~\\cm\\ for frequencies in the fundamental bands and 0.4~\\cm\\ for those in the first overtone and lowest combination bands. For the intensities, the calculated and experimental values differ by 0.3\\% and 40\\% for the fundamentals and overtones, respectively. The optimized PES and DMF are used to calculate the room-temperature ro-vibrational spectrum. These calculation reproduce...

Pavlyuchko, A I; Tennyson, Jonathan

2014-01-01

96

An efficient approach for calculating vibrational wave functions and zero-point vibrational corrections to molecular properties of polyatomic molecules  

NASA Astrophysics Data System (ADS)

We have recently presented a formalism for calculating zero-point vibrational corrections to molecular properties of polyatomic molecules in which the contribution to the zero-point vibrational correction from the anharmonicity of the potential is included in the calculations by performing a perturbation expansion of the vibrational wave function around an effective geometry. In this paper we describe an implementation of this approach, focusing on computational aspects such as the definition of normal coordinates at a nonequilibrium geometry and the use of the Eckart frame in order to obtain accurate nonisotropic molecular properties. The formalism allows for a black-box evaluation of zero-point vibrational corrections, completed in two successive steps, requiring a total of two molecular Hessians, 6K-11 molecular gradients, and 6K-11 property evaluations, K being the number of atoms. We apply the approach to the study of a number of electric and magnetic properties—the dipole and quadrupole moments, the static and frequency-dependent polarizability, the magnetizability, the rotational g tensor and the nuclear shieldings—of the molecules hydrogen fluoride, water, ammonia, and methane. Particular attention is paid to the importance of electron correlation and of the importance of the zero-point vibrational corrections for obtaining accurate estimates of molecular properties for a direct comparison with experiment.

Ruud, Kenneth; Åstrand, Per-Olof; Taylor, Peter R.

2000-02-01

97

Accurate calculation of vibrational frequencies using explicitly correlated coupled-cluster theory.  

PubMed

The recently proposed explicitly correlated CCSD(T)-F12x (x = a,b) approximations [T. B. Adler, G. Knizia, and H.-J. Werner, J. Chem. Phys. 127, 221106 (2007)] are applied to compute equilibrium structures and harmonic as well as anharmonic vibrational frequencies for H(2)O, HCN, CO(2), CH(2)O, H(2)O(2), C(2)H(2), CH(2)NH, C(2)H(2)O, and the trans-isomer of 1,2-C(2)H(2)F(2). Using aug-cc-pVTZ basis sets, the CCSD(T)-F12a equilibrium geometries and harmonic vibrational frequencies are in very close agreement with CCSD(T)/aug-cc-pV5Z values. The anharmonic frequencies are evaluated using vibrational self-consistent field and vibrational configuration interaction methods based on automatically generated potential energy surfaces. The mean absolute deviation of the CCSD(T)-F12a/aug-cc-pVTZ anharmonic frequencies from experimental values amounts to only 4.0 cm(-1). PMID:19206956

Rauhut, Guntram; Knizia, Gerald; Werner, Hans-Joachim

2009-02-01

98

Calculation of harmonic generation during the multiphoton ionization of the hydrogen atom  

SciTech Connect

The response of a hydrogen atom to an intense nonresonant laser field is investigated by direct numerical solution of the time-dependent Schroedinger equation. This calculation is nonperturbative and does not involve the eigenstates of the field-free atom. An ionization rate for three-photon ionization is calculated and found to be in excellent agreement with previous values. The time-dependent electric dipole moment is calculated; its Fourier transform yields the spectrum of scattered light. Odd-order harmonic peaks through at least the 25th order are present in the spectrum.

DeVries, P.L. (Department of Physics, Miami University, Oxford, Ohio 45056 (USA))

1990-04-01

99

Mode complexity in a harmonically forced string with a local spring-damper and transitions from vibrations to waves  

NASA Astrophysics Data System (ADS)

We numerically and analytically investigate the dynamics of a linear, uniform, homogeneous, undamped string coupled to a linear spring-dashpot system at its center and fixed to ground at its ends. Both ends of the string are excited through identical and synchronous harmonic motion, and the steady-state dynamics of the system is analytically studied. The localized damping introduces mode complexity, which results in spatial shifting of the peak resonance amplitudes to different locations of the string and highly nontrivial phase variations confined to certain predictable boundary layers of the string. We find that there exists a unique combination of system parameters such that mode complexity reaches an absolute maximum: in such an optimal case, damping destroys all the normal modes of vibration, and instead, traveling waves are formed. This peak in complexity marks the transition between very weak and very strong damping effects and provides a direct mode complexity-induced transition from vibrations (standing waves) to traveling waves.

Blanchard, Antoine; Gendelman, Oleg V.; Michael McFarland, D.; Bergman, Lawrence A.; Vakakis, Alexander F.

2015-01-01

100

Calculation of vibrational relaxation times in multi-component excitable gases  

NASA Astrophysics Data System (ADS)

In the research field of acoustic propagation in excitable gases, one of the most critical parameters is the vibrational relaxation time, which determines the frequency of the acoustic dispersion step or the absorption maximum. In this paper, the vibrational relaxation equations given by Tanczos [J. Chem. Phys. 25, 439 (1956)] have been applied to calculate the vibrational multi-relaxation times in multi-component gases. The eigenvalues of the energy-transition-rate matrix are proven to be the reciprocals of the multi-relaxation times. Comparisons demonstrate that our relaxation frequencies calculated for various gas compositions, including carbon dioxide, methane, chlorine, nitrogen, and oxygen, agree with the experimental data.

Zhang, Ke-Sheng; Ou, Weihua; Jiang, Xueqin; Long, Fei; Hu, Mingzhe

2014-10-01

101

Molecular structure, vibrational analysis (FT-IR, FT-Raman), NMR, UV, NBO and HOMO-LUMO analysis of N,N-Diphenyl Formamide based on DFT calculations.  

PubMed

In this work, the vibrational spectral analysis is carried out by using Raman and infrared spectroscopy in the range 4000-400cm(-1) and 4000-50cm(-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

Mathammal, R; Monisha, N R; Yasaswini, S; Krishnakumar, V

2015-03-15

102

Calculation of the convex roof for an open entangled harmonic oscillator system  

SciTech Connect

We explicitly calculate the time dependence of entanglement via the convex roof extension for a system of noninteracting harmonic oscillators. These oscillators interact only indirectly with each other by way of a zero-temperature bath. The initial state of the oscillators is taken to be that of an entangled Schroedinger-cat state. This type of initial condition leads to superexponential decay of the entanglement when the initial state has the same symmetry as the interaction Hamiltonian.

Landau, Mayer A.; Stroud, C. R. Jr. [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States)

2010-05-15

103

DFT calculation and vibrational spectroscopic studies of 2-(tert-butoxycarbonyl (Boc) -amino)-5-bromopyridine  

NASA Astrophysics Data System (ADS)

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.

Premkumar, S.; Jawahar, A.; Mathavan, T.; Kumara Dhas, M.; Sathe, V. G.; Milton Franklin Benial, A.

2014-08-01

104

Calculation of flight vibration levels of the AH-1G helicopter and correlation with existing flight vibration measurements  

NASA Technical Reports Server (NTRS)

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.

Sopher, R.; Twomey, W. J.

1990-01-01

105

First Principles Phase Diagram Calculations for the System NaCl-KCl: the role of excess vibrational entropy.  

E-print Network

First Principles Phase Diagram Calculations for the System NaCl-KCl: the role of excess vibrational- and without an approximation for the excess vibrational entropy (SV IB). Including SV IB dramatically improvesK}Calc. Key words: NaCl-KCl; First Principles; Phase diagram calculation; Excess vibrational entropy

Burton, Benjamin P.

106

Calculation of optical second-harmonic susceptibilities and optical activity for crystals  

SciTech Connect

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.

Levine, Z.H. [Ohio State Univ., Columbus, OH (United States)

1994-12-31

107

Inclusion of nonadiabiatic effects in calculations on vibrational excitation of molecular hydrogen by low-energy electron impact  

E-print Network

Inclusion of nonadiabiatic effects in calculations on vibrational excitation of molecular hydrogen September 1998 The nonadiabatic phase matrix method offers a unified, systematic treatment of vibrational fully adiabatic counterpart, the energy-modified adiabatic method--includes nonadiabatic effects, which

Morrison, Michael A.

108

Revised calculation of four-particle harmonic-oscillator transformation brackets matrix  

NASA Astrophysics Data System (ADS)

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).

Mickevi?ius, S.; Germanas, D.; Kalinauskas, R. K.

2013-02-01

109

Density functional theory calculations of pressure effects on the vibrational structure of alpha-RDX.  

PubMed

Pressure effects on the vibrational structure of alpha-RDX were examined using density functional theory (DFT) up to 4 GPa. The calculated vibrational frequencies at ambient conditions are in better agreement with experimental data than are previous single molecule calculations. The calculations showed the following pressure-induced changes: (i) larger shifts for lattice modes and for internal modes associated with the CH(2) and NO(2) groups as compared to the pressure shifts for modes associated with the triazine ring, (ii) enhancement of mixing between different vibrations, for example, between NN stretching and CH(2) scissor, wagging, twisting vibrations, and (iii) increase in mixing between translational lattice vibrations and the NO(2) wagging vibrations, reducing the distinction between internal and lattice modes. The calculated volume and lattice constants at ambient pressure are larger than the experimental values, due to the inability of the present density functional approach to correctly account for van der Waals forces. Consequently, the pressure-induced frequency shifts of many modes deviate substantially from experimental data for pressures below 1 GPa. With increasing pressure, both the lattice constants and the frequency shifts agree more closely with experimental values. PMID:18973322

Miao, M S; Dreger, Z A; Winey, J M; Gupta, Y M

2008-11-27

110

A thermal self-consistent field theory for the calculation of molecular vibrational partition functions.  

PubMed

A new approach for the calculation of anharmonic molecular vibrational partition functions is developed based on a separable ansatz to the thermal density matrix. The parameters appearing in the effective single particle Hamiltonians that generate the thermal density matrices are determined variationally. The resulting equations are the thermal analogs of the vibrational self-consistent field approximation. The method has the formal property that the free energy calculated by this approach is an upper bound to the exact free energy. Thermodynamic quantities calculated by this approach are generally in good agreement with the results of numerically converged calculations. This approach is more efficient than the standard sum over state approaches in that the computational resources scale with N(4) where N is the number of vibrational degrees of freedom. Thus it can be applied to fairly large systems. PMID:19778095

Roy, Tapta Kanchan; Prasad, M Durga

2009-09-21

111

Microwave, structural, conformational, vibrational studies and ab initio calculations of isocyanocyclopentane  

NASA Astrophysics Data System (ADS)

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); C?sbnd N = 1.432 (3); C?sbnd C?,C?? = 1.534 (3); C?sbnd C?,C?? = 1.542 (3); C?sbnd C?? = 1.554 (3) and angles (°): ?C?sbnd Ntbnd C = 177.8 (5); ?C?C?sbnd N = 110.4 (5); ?C?C?C?? = 102.9 (5); ?C?C?C? = 103.6 (5); ?C?C?C?? = 105.9 (5). The results are discussed and compared to the corresponding properties of some related molecules.

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

112

Molecular geometry and vibrational studies of 3,5-diamino-1,2,4-triazole using quantum chemical calculations and FT-IR and FT-Raman spectroscopies.  

PubMed

The 3,5-diamino-1,2,4-triazole (guanazole) was investigated by vibrational spectroscopy and quantum methods. The solid phase FT-IR and FT-Raman spectra were recorded in the region 4000-400 cm(-1) and 3600-50 cm(-1) respectively, and the band assignments were supported by deuteration effects. The results of energy calculations have shown that the most stable form is 1H-3,5-diamino-1,2,4-triazole under C1 symmetry. For this form, the molecular structure, harmonic vibrational wave numbers, infrared intensities and Raman activities were calculated by the ab initio/HF and DFT/B3LYP methods using 6-31G* basis set. The calculated geometrical parameters of the guanazole molecule using B3LYP methodology are in good agreement with the previously reported X-ray data, and the scaled vibrational wave number values are in good agreement with the experimental data. The normal vibrations were characterized in terms of potential energy distribution (PEDs) using VEDA 4 program. PMID:21112810

Guennoun, L; El jastimi, J; Guédira, F; Marakchi, K; Kabbaj, O K; El Hajji, A; Zaydoun, S

2011-01-01

113

Floquet calculation of harmonic generation from hydrogen molecular ions in strong monochromatic laser fields  

E-print Network

We present Floquet calculations of high harmonic generation (HHG) for the lowest two electronic states of the $\\mbox{H}_2^+$ ion by strong continuous-wave laser fields. We solve the non-Hermitian matrix problem to get accurate solutions to the periodic time-dependent Schr\\"odinger equation (TDSE) by applying a pseudospectral representation combined with a complex absorbing potential method. This represents an alternative approach to direct TDSE solutions to obtain the harmonic spectra for the ion. We compare our HHG rates for the lower and upper states of $\\mbox{H}^{+}_{2}$, which correspond to the gerade and ungerade ground states in the field-free case, with previously obtained results in the literature. We show that the enhancement of the ionization rates at the critical internuclear separation $R_{c}\\approx 8\\,au$ plays some role in the appearance of very strong harmonic orders $n=5-11$ at $\\lambda = 1064\\,nm$ and $n=5-9$ at $\\lambda = 800\\,nm$ and intensity $I=10^{14}\\,W/cm^{2}$.

Tsogbayar, Ts

2014-01-01

114

Application of a Spherical Harmonics Expansion Approach for Calculating Ligand Density Distributions around Proteins.  

PubMed

Protein-ligand interactions are central to many biological applications, including molecular recognition, protein formulations, and bioseparations. Complex, multisite ligands can have affinities for different locations on a protein's surface, depending on the chemical and topographical complementarity. We employ an approach based on the spherical harmonic expansion to calculate spatially resolved three-dimensional atomic density profiles of water and ligands in the vicinity of macromolecules. To illustrate the approach, we first study the hydration of model C180 buckyball solutes, with nonspherical patterns of hydrophobicity/-philicity on their surface. We extend the approach to calculate density profiles of increasingly complex ligands and their constituent groups around a protein (ubiquitin) in aqueous solution. Analysis of density profiles provides information about the binding face of the protein and the preferred orientations of ligands on the binding surface. Our results highlight that the spherical harmonic expansion based approach is easy to implement and efficient for calculation and visualization of three-dimensional density profiles around spherically nonsymmetric and topographically and chemically complex solutes. PMID:25198149

Parimal, Siddharth; Cramer, Steven M; Garde, Shekhar

2014-11-20

115

Calculated vibrational properties of pigments in protein binding sites  

PubMed Central

FTIR difference spectroscopy is widely used to probe molecular bonding interactions of protein-bound electron transfer cofactors. The technique is particularly attractive because it provides information on both neutral and radical cofactor states. Such dual information is not easily obtainable using other techniques. Although FTIR difference spectroscopy has been used to study cofactors in biological protein complexes, in nearly all cases interpretation of the spectra has been purely qualitative. Virtually no computational work has been undertaken in an attempt to model the spectra. To address this problem we have developed the use of ONIOM (our own N-layered integrated molecular Orbital + Molecular mechanics package) (quantum mechanical:molecular mechanics) methods to calculate FTIR difference spectra associated with protein-bound cofactors. As a specific example showing the utility of the approach we have calculated isotope edited FTIR difference spectra associated with unlabeled and labeled ubiquinones in the QA binding site in Rhodobacter sphaeroides photosynthetic reaction centers. The calculated spectra are in remarkable agreement with experiment. Such agreement cannot be obtained by considering ubiquinone molecules in the gas phase or in solution. A calculation including the protein environment is required. The ONIOM calculated spectra agree well with experiment but indicate a very different interpretation of the experimental data compared to that proposed previously. In particular the calculations do not predict that one of the carbonyl groups of QA is very strongly hydrogen bonded. We show that a computational-based interpretation of FTIR difference spectra associated with protein-bound cofactors is now possible. This approach will be applicable to FTIR studies of many cofactor-containing proteins. PMID:21670247

Lamichhane, Hari Prasad; Hastings, Gary

2011-01-01

116

PHYSICAL REVIEW B 85, 224303 (2012) Mixed-space approach for calculation of vibration-induced dipole-dipole interactions  

E-print Network

; published 19 June 2012) By explicitly taking into account the effects of vibration-induced dipole for the effects of vibration-induced dipole-dipole interactions on the phonon frequencies of an ionic crystalPHYSICAL REVIEW B 85, 224303 (2012) Mixed-space approach for calculation of vibration

Chen, Long-Qing

117

Transformation of potential energy surfaces for estimating isotopic shifts in anharmonic vibrational frequency calculations.  

PubMed

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. PMID:24832257

Meier, Patrick; Oschetzki, Dominik; Berger, Robert; Rauhut, Guntram

2014-05-14

118

Critical free vibrations of screw centrifuges and calculation of damping devices  

SciTech Connect

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.

Fainerman, I.A.

1985-05-01

119

Transformation of potential energy surfaces for estimating isotopic shifts in anharmonic vibrational frequency calculations  

SciTech Connect

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.

Meier, Patrick; Oschetzki, Dominik; Rauhut, Guntram, E-mail: rauhut@theochem.uni-stuttgart.de [Institut für Theoretische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart (Germany)] [Institut für Theoretische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart (Germany); Berger, Robert [Clemens-Schöpf Institut für Organische Chemie and Biochemie, Technische Universität Darmstadt, Petersenstrasse 22, 64287 Darmstadt (Germany)] [Clemens-Schöpf Institut für Organische Chemie and Biochemie, Technische Universität Darmstadt, Petersenstrasse 22, 64287 Darmstadt (Germany)

2014-05-14

120

Vibrational Spectrum of (CO)2 on Cu(100): Quantum Calculations with 18 Coupled Mode  

NASA Technical Reports Server (NTRS)

We report calculations of the vibrational frequencies of CO dimer on Cu(100) using recently developed vibrational self-consistent field code. Eighteen modes are treated explicitly within three modes coupling representation. Nine symmetry distinct doublets are observed and the corresponding frequencies are computed. The thermally broadened spectrum of the CO-stretch fundamental is calculated at various temperatures. Both the temperature and coverage dependence of both the average CO-stretch frequency and the corresponding line-width are consistent with experimentally observed trends. The document contains no classified information International clearance is needed.

Dzegilenko, Fedor; Bowman, Joel M.; Carter, Stuart; Saini, Subhash (Technical Monitor)

1998-01-01

121

A new experimental and theoretical investigation on the structures of aminoethyl phosphonic acid in aqueous medium based on the vibrational spectra and DFT calculations  

NASA Astrophysics Data System (ADS)

A new study on the structural and vibrational properties of the aminoethylphosphonic acid was performed in aqueous solution phase by using the self-consistent reaction field (SCRF) method. We have studied and characterized it by infrared and Raman spectroscopies in solid and aqueous solution phases. The Density Functional Theory (DFT) method with Pople's basis set show that three stable zwitterions for the title molecule have been theoretically determined in aqueous solution and that probably they are present in it medium. Here, the solvent effects were studied by means of the self-consistent reaction field (SCRF) method with the polarized continuum model (PCM). The harmonic vibrational frequencies for the optimized geometries of the three zwitterions were calculated at the B3LYP/6-31G? level of the theory. A complete assignment of the IR and Raman spectra of the compound in aqueous solution was performed combining the DFT calculations with Pulay's Scaled Quantum Mechanics Force Field (SQMFF) methodology in order to fit the theoretical frequency values to the experimental ones. Moreover, Natural Bond Orbital (NBO) and topological properties calculations were performed to analyze the energies and geometrical parameters of its three zwitterions in aqueous medium as well as the magnitude of the intramolecular interactions. The bond orders, atomic charges, solvation energies, dipole moments, molecular electrostatic potentials and force constants parameters calculated for zwitterions in aqueous solution, may be used to gain chemical and vibrational insights into related compounds.

Roldán, María L.; Ledesma, Ana E.; Raschi, Ana B.; Castillo, María V.; Romano, Elida; Brandán, Silvia A.

2013-06-01

122

Calculations of the vibrational frequency and isotopic shift of UF6 and U2F6  

NASA Astrophysics Data System (ADS)

Molecular structure, vibrational frequency and infrared intensity of UF6 are investigated by using the revised Perdew—Burke—Enzerhof function with the triple-zeta polarized basis set. The calculation results are in good agreement with the experimental values and indicate the existence of a stable U2F6 molecule with a multiple bonded U2 unit. The calculation results also predict that the D3d symmetry of U2F6 is more stable than D3h. The optimized geometries, vibrational frequencies, and infrared intensities are also reported for U2F6 molecules in D3d symmetry. In addition, the isotopic shift of vibrational frequencies of the two molecules under isotopic substitution of uranium atom are also investigated with the same method. The U2F6 molecule is predicted to be better than UF6 for laser uranic isotope separation.

Zhang, Yun-Guang; Zha, Xin-Wei

2012-07-01

123

[Chloro(difluoro)acetyl]phosphoramidic acid dichloride ClF 2CC(O)NHP(O)Cl 2, synthesis, vibrational and NMR spectra and theoretical calculations  

NASA Astrophysics Data System (ADS)

The synthesis of a new carbacylamidophosphate compound, [chloro(difluoro)acetyl]phosphoramidic acid dichloride (ClF 2CC(O)NHP(O)Cl 2), is reported along with its FTIR, Raman and mass spectra. The theoretical vibrational spectra were used to perform a tentative assignment of the observed bands. Quantum chemical calculations were realized with ab initio and density functional theory (DFT) methods using different levels of approximation. The title compound was analyzed as a dimer with C i symmetry (C dbnd O double bond in anti position with respect to the P dbnd O double bond). The simulation of the potential energy surface was performed varying the dihedral angles ?(Cl sbnd C sbnd C sbnd N) and ?(C sbnd C sbnd N sbnd P) using HF and B3LYP methods. The harmonic vibrations obtained by all theoretical methods are in good agreement with the experimental results. 1H, 13C and 31P NMR are also reported.

Iriarte, Ana G.; Erben, Mauricio F.; Gholivand, Khodayar; Jios, Jorge L.; Ulic, Sonia E.; Della Védova, Carlos O.

2008-08-01

124

Tuning natural modes of vibration by prestress in the design of a harmonic gong.  

PubMed

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

McLachlan, Neil; Adams, Ryan; Burvill, Colin

2012-01-01

125

Calculation of the vibrational spectra of ?-rdx using the grimme DFT potential  

NASA Astrophysics Data System (ADS)

The density-functional theory (DFT) potential by Grimme has been proposed for describing longrange dispersion corrections. This potential has been implemented into the CRYSTAL09 program and used to calculate the vibrational spectra in ?-RDX at equilibrium. The frequencies and intensities are reported and compared with prior theory and experiment where possible.

Perger, Warren; Slough, William J.; Valenzano, Loredana; Flurchick, K. M.

2012-03-01

126

Programmable Calculator Use in Undergraduate Dynamics, Vibrations, and Elementary Structures Courses.  

ERIC Educational Resources Information Center

Presents programmable calculator solutions to selected problems, including area moments of inertia and principal values, the 2-D principal stress problem, C.G. and pitch inertia computations, 3-D eigenvalue problems, 3 DOF vibrations, and a complex flutter determinant. (SK)

Cutchins, M. A.

1982-01-01

127

Decentralized harmonic active vibration control of a flexible plate using piezoelectric actuator-sensor pairs.  

PubMed

We have investigated decentralized active control of periodic panel vibration using multiple pairs combining PZT actuators and PVDF sensors distributed on the panel. By contrast with centralized MIMO controllers used to actively control the vibrations or the sound radiation of extended structures, decentralized control using independent local control loops only requires identification of the diagonal terms in the plant matrix. However, it is difficult to a priori predict the global stability of such decentralized control. In this study, the general situation of noncollocated actuator-sensor pairs was considered. Frequency domain gradient and Newton-Raphson adaptation of decentralized control were analyzed, both in terms of performance and stability conditions. The stability conditions are especially derived in terms of the adaptation coefficient and a control effort weighting coefficient. Simulations and experimental results are presented in the case of a simply supported panel with four PZT-PVDF pairs distributed on it. Decentralized vibration control is shown to be highly dependent on the frequency, but can be as effective as a fully centralized control even when the plant matrix is not diagonal-dominant or is not strictly positive real (not dissipative). PMID:16454282

Baudry, Matthieu; Micheau, Philippe; Berry, Alain

2006-01-01

128

Theoretical calculation and vibrational spectral analysis of L-arginine trifluoroacetate  

NASA Astrophysics Data System (ADS)

Fourier transform infrared and Raman spectra of the nonlinear optical crystal, L-arginine trifluoroacetate ( L-arginine·CF 3COOH, abbreviated as LATF) have been calculated by the first-principles calculation and investigated in experiment. The calculated results are slightly different from those experimental values because of the distinction resulted from the intermolecular hydrogen bonds. The role of this type of intermolecular interaction on the crystal vibrational spectra and nonlinear optical properties has been discussed. The absorption-edge on the IR side has been estimated by the theoretical approach on basis of the calculated infrared spectrum, which will be meaningful for further research on NLO crystal.

Sun, Z. H.; Zhang, L.; Xu, D.; Wang, X. Q.; Liu, X. J.; Zhang, G. H.

2008-11-01

129

Studies of the molecular geometry, vibrational spectra, frontier molecular orbital, nonlinear optical and thermodynamics properties of aceclofenac by quantum chemical calculations.  

PubMed

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 (?) and the first order hyper polarizability (?) 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

Suresh, S; Gunasekaran, S; Srinivasan, S

2014-05-01

130

Studies of the molecular geometry, vibrational spectra, Frontier molecular orbital, nonlinear optical and thermodynamics properties of Aceclofenac by quantum chemical calculations  

NASA Astrophysics Data System (ADS)

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 (?) and the first order hyper polarizability (?) 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.

Suresh, S.; Gunasekaran, S.; Srinivasan, S.

131

2D calculation of anharmonic OH vibrations in a layered hydroxide crystal.  

PubMed

Anharmonic vibrational frequencies for the Raman-active (A(1g)) and the IR-active (A(2u)) modes have been calculated for the LiOH crystal within a plane-wave density functional theory (DFT) framework. We find that a two-dimensional quantum-mechanical vibrational approach, allowing for anharmonic coupling between symmetric and antisymmetric OH stretching modes, produces OH frequencies--both absolute frequencies and gas-to-solid frequency shifts--in good agreement with experiment. Remaining errors in the absolute frequencies are largely a consequence of the DFT model chosen. A one-dimensional normal-mode following vibrational treatment, on the other hand, fails to reproduce both absolute anharmonic frequencies and gas-to-solid frequency shifts. PMID:18715080

Gajewski, Grzegorz; Mitev, Pavlin D; Hermansson, Kersti

2008-08-14

132

Examination of super-harmonics in a multi-degree of freedom nonlinear vibration isolation system: Refined models and comparison with measurements  

NASA Astrophysics Data System (ADS)

A multi-degree of freedom vibration isolation experiment consisting of a powertrain, three powertrain mounts including a dynamic load sensing hydraulic mount, a sub-frame, and 4 bushings is examined in both time and frequency domains. Since the hydraulic mount exhibits nonlinear phenomena, super-harmonics are observed in motion, pressure and interfacial force measurements when the system is sinusoidally excited. Refined indirect force estimation methods are proposed with a focus on the super-harmonics. This includes the development of a quasi-linear fluid system model with embedded spectrally varying and amplitude-sensitive parameters. The reverse path spectral method is employed using the measured relative motion and upper chamber pressure in the nonlinear hydraulic mount. The relevant transfer functions (with effective parameters for both rubber and hydraulic paths) are used to estimate the interfacial forces. Up to six harmonics of the fundamental excitation frequency are examined, and the contribution of each path is clarified. The proposed quasi-linear fluid system model including super-harmonics extends prior work on indirect force estimation methods and successfully predicts the interfacial forces in the multi-degree of freedom vibration isolation system. The quasi-linear fluid system model, however, seems to be inadequate in estimating the sub-harmonic responses.

Yoon, Jong-Yun; Singh, Rajendra

2014-10-01

133

A statistical approach to the calculation of harmonics in MV systems caused by dispersed LV customers  

Microsoft Academic Search

Problems usually arise when predicting harmonics in public supply systems due to the varying characteristics of the loads connected. Based on comprehensive measurements, a statistical load model is set up providing the harmonic parameters of all LV systems fed by the same HV\\/MV feeder. Harmonic distortion in the MV system caused by the variety of stochastic LV customers is determined

T. Goeke

1995-01-01

134

RESEARCH NOTE: On the efficient calculation of ordinary and generalized spherical harmonics  

NASA Astrophysics Data System (ADS)

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.

Masters, Guy; Richards-Dinger, Keith

1998-10-01

135

Dynamic (hyper)polarizabilities of the sulphur dioxide molecule: Coupled cluster calculations including vibrational corrections  

NASA Astrophysics Data System (ADS)

In this work we report results for dynamical (hyper)polarizabilities of the sulphur dioxide molecule with inclusion of vibrational corrections. The electronic contributions were computed analytically at the single and double coupled cluster level through response theories for the frequencies 0, 0.0239, 0.0428, 0.0656, 0.0720, and 0.0886 hartree. Contributions of the connected triple excitations to the dynamic electronic properties were also estimated through the multiplicative correction scheme. Vibrational corrections were calculated by means of the perturbation theoretical method. The results obtained show that the zero point vibrational correction is very small for all properties studied while the pure vibrational correction is relevant for the dc-Pockels effect, intensity dependent refractive index, and dc-Kerr effect. For these nonlinear optical processes, the pure vibrational corrections represent approximately 75%, 13%, and 6% of the corresponding electronic contributions for the higher frequencies quoted. The results presented for the polarizability are in good agreement with experimental values available in the literature. For the hyperpolarizabilities we have not obtained experimental results with precision sufficient for comparison.

Naves, Emílio S.; Castro, Marcos A.; Fonseca, Tertius L.

2012-01-01

136

Vibration  

NASA Technical Reports Server (NTRS)

Man's reactions to vibration are emphasized rather than his reactions to the vibrational characteristics of vehicles. Vibrational effects studies include: performance effects reflected in tracking proficiency, reaction time, visual impairment, and other measures related to man's ability to control a system; physiological reactions; biodynamic responses; subjective reactions; and human tolerance limits. Technological refinements in shaker systems and improved experimental designs are used to validate the data.

Hornick, R. J.

1973-01-01

137

Active vibration control of a ring-stiffened cylindrical shell in contact with unbounded external fluid and subjected to harmonic disturbance by piezoelectric sensor and actuator  

NASA Astrophysics Data System (ADS)

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.

Kwak, Moon K.; Yang, Dong-Ho

2013-09-01

138

Fluorescence excitation and ultraviolet absorption spectra and theoretical calculations for benzocyclobutane: Vibrations and structure of its excited S{sub 1}(?,?{sup *}) electronic state  

SciTech Connect

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}(?,?{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}(?,?{sup *}) 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 S{sub 0} and S{sub 1}(?,?{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}(?,?{sup *}) excited state.

Shin, Hee Won; Ocola, Esther J.; Laane, Jaan, E-mail: laane@mail.chem.tamu.edu [Department of Chemistry, Texas A and M University, College Station, Texas 77843-3255 (United States)] [Department of Chemistry, Texas A and M University, College Station, Texas 77843-3255 (United States); Kim, Sunghwan [National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Department of Health and Human Services, 8600 Rockville Pike, Bethesda, Maryland 20894 (United States)] [National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Department of Health and Human Services, 8600 Rockville Pike, Bethesda, Maryland 20894 (United States)

2014-01-21

139

Fluorescence excitation and ultraviolet absorption spectra and theoretical calculations for benzocyclobutane: Vibrations and structure of its excited S1(?,?*) electronic state  

PubMed Central

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.; Kim, Sunghwan; Laane, Jaan

2014-01-01

140

Comparison of algorithms for the calculation of molecular vibrational level densities.  

PubMed

Level densities of vibrational degrees of freedom are calculated numerically with formulas based on the inversion of the canonical vibrational partition function. The calculated level densities are compared with other approximate equations from literature and with the exact Beyer-Swinehart values, for which a simplified but equivalent version is given. All approximate equations agree at high excitation energies, but our results are vastly superior at low energies for large molecules. The results presented here are therefore of particular relevance for thermal processes of very large molecules, e.g., of biological nature, for which the exact state counting can be prohibitively slow. Furthermore, it is valid for situations where anharmonic motion significantly influences the thermal properties. PMID:18500852

Hansen, K

2008-05-21

141

Ab initio rotation-vibration energies of HOC + calculated using the nonrigid bender Hamiltonian  

NASA Astrophysics Data System (ADS)

In a previous paper [W. P. Kraemer and P. R. Bunker, J. Mol. Spectrosc.101, 379-394 (1983)] the results of configuration interaction calculations, performed in order to investigate the bending potential of the molecular ion HOC +, were reported. In the present paper we give the results of such calculations including additional points on the potential surface chosen mainly in order to study the HO and OC stretching potentials at longer bond lengths. We have determined the rotation-vibration energies from this extended potential surface using a newly written computer program that diagonalizes the nonrigid bender Hamiltonian. We compare the results with those obtained using the second-order rotation-vibration perturbation Hamiltonian, the rigid bender Hamiltonian, and the semirigid bender Hamiltonian.

Beardsworth, R.; Bunker, P. R.; Jensen, Per; Kraemer, W. P.

1986-07-01

142

Full dimensional Franck-Condon factors for the acetylene tilde{{A}} 1Au—{tilde{X}} {^1? _g^+} transition. I. Method for calculating polyatomic linear—bent vibrational intensity factors and evaluation of calculated intensities for the gerade vibrational modes in acetylene  

NASA Astrophysics Data System (ADS)

Franck-Condon vibrational overlap integrals for the tilde{A} {^1A_u}—{tilde{X}} {^1? _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 wavefunction for the out-of-plane component of the trans bending mode, ? _4^' ' }, 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, ? _5^' ' }, 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 tilde{A}-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 tilde{A} {^1A_u}—{tilde{X}} {^1? _g^+} transition. II. Vibrational overlap factors for levels involving excitation in ungerade modes," J. Chem. Phys. 141, 134305 (2014)].

Park, G. Barratt

2014-10-01

143

How to calculate the vibration of an inhomogeneous string using MATLAB programs  

NSDL National Science Digital Library

This paper presents a solution to the dynamics of a vibrating inhomogeneous string by the method of separation of variables in x and t. The solution consists in transforming the differential equation in x into an integral equation, which is subsequently solved by means of a spectral method. As an extension of a paper in the American Journal of Physics, this material describes and makes available the MATLAB programs required for the spectral calculations.

Rawitscher, George

2011-07-31

144

Conformational stability, vibrational spectra, molecular structure, NBO and HOMO-LUMO analysis of 5-nitro-2-furaldehyde oxime based on DFT calculations.  

PubMed

The FTIR and FT-Raman spectra of 5-nitro-2-furaldehyde oxime (NFAO) have been recorded in the regions 4000-400 cm(-1) and 3500-50 cm(-1), respectively. The total energies of different conformations have been obtained from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. The computational results identify the most stable conformer of NFAO as the C1 form. 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 optimum molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, were calculated by density functional theory (DFT/B3LYP) method with 6-31+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. A detailed interpretation of the infrared and Raman spectra of NFAO is also reported based on total energy distribution (TED). Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. Besides, molecular electrostatic potential (MEP), HOMO and LUMO analysis, and several thermodynamic properties were performed by the DFT method. Mulliken's net charges have been calculated and compared with the natural atomic charges. Ultraviolet-visible spectrum of the title molecule has also been calculated using TD-DFT method. PMID:23274252

Arivazhagan, M; Jeyavijayan, S; Geethapriya, J

2013-03-01

145

A refined quartic potential energy surface and large scale vibrational calculations for S0 thiophosgene.  

PubMed

In this work we present a full 6D quartic potential energy surface (PES) for S0 thiophosgene in curvilinear symmetrized bond-angle coordinates. The PES was refined starting from an ab initio field derived from acc-pVTZ basis set with CCSD(T) corrections for electron correlation. In the present calculations we used our variational method that was recently tested on formaldehyde and some of its isotopomers, along with additional improvements. The lower experimentally known vibrational levels for (35)Cl2CS were reproduced quite well in the calculations, which can be regarded as a test for the feasibility of the obtained quartic PES. PMID:25615683

Rashev, Svetoslav; Moule, David C

2015-04-01

146

Vibrational and thermodynamic properties of orthorhombic CaSnO3 from DFT and DFPT calculations  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) and density functional perturbation theory (DFPT) calculations were used to investigate the vibrational and thermodynamic properties of orthorhombic stannate CaSnO3 compound. Our approach was based on the generalized gradient approximation with dispersion correction (GGA+D), considering the norm-conserved pseudopotentials. The phonon dispersion relation as well as theoretical peaks of the infrared (IR) and Raman spectrum in the frequency range of 100-800 cm-1 was analyzed and assigned. The thermodynamic potentials and the specific heat at constant volume of the CaSnO3 compound are also calculated, whose dependence with the temperature are discussed.

Moreira, E.; Barboza, C. A.; Albuquerque, E. L.; Fulco, U. L.; Henriques, J. M.; Araújo, A. I.

2015-02-01

147

Vibrational spectroscopy of beryllium aluminosilicates: Heat capacity calculations from band assignments  

NASA Astrophysics Data System (ADS)

Far-infrared, mid-IR, and Raman powder spectra were measured on six phases (bromellite, chrysoberyl, phenakite, bertrandite, beryl, and euclase) in the system BeO-Al2O3-SiO2-H2O. A single-crystal absorption spectrum of IR fundamentals in beryl is also presented, which more closely resembles the powder absorption spectrum than it does absorption spectra calculated from single-crystal reflection data. Assignments of the SiO4 and BeO4 internal vibrations are made in accordance with each mineral's symmetry and composition and by comparison to structural analogs. Heat capacities C v calculated for these partial band assignments agree with C v derived from experimental C p for all six phases, provided that Kieffer's (1979c) model is slightly modified to correctly enumerate both Si-O and Be-O stretching modes in the high frequency region (>750 cm-1). Si-O stretching bands were found to out-number Be-O stretching modes in the high-energy region of the vibrational spectra with two exceptions: (1) For those phases containing oxygen ions not coordinated to silicon, vibrations occurring at v>1,080 cm-1 that are attributable to Be-O (H) stretching must be treated separately in the model in order to calculate C v accurately. (2) Minerals consisting entirely of interlocking Si and Be tetrahedra (i.e., phases without Al or OH) can be modeled by one optic continuum representing all optical modes. These results, along with the occurrence of very low energy lattice vibrations for Be-silicates within Al, suggests that although Be-O bonds are generally weaker than neighboring Si-O bonds, Be mimics the network-forming characteristic of Si to a limited extent.

Hofmeister, A. M.; Hoering, T. C.; Virgo, D.

1987-03-01

148

Ab initio calculations of anharmonic vibrational spectroscopy for hydrogen fluoride (HF)n (n = 3, 4) and mixed hydrogen fluoride/water (HF)n(H2O)n (n = 1, 2, 4) clusters.  

PubMed

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 Møller-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. PMID:11991501

Chaban, Galina M; Gerber, R Benny

2002-03-01

149

Ab initio calculations of anharmonic vibrational spectroscopy for hydrogen fluoride (HF)n (n = 3, 4) and mixed hydrogen fluoride/water (HF)n(H2O)n (n = 1, 2, 4) clusters  

NASA Technical Reports Server (NTRS)

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.

Chaban, Galina M.; Gerber, R. Benny

2002-01-01

150

Ab Initio Calculations of Anharmonic Vibrational Spectroscopy for Hydrogen Fluoride (HF)n (n=3,4) and Mixed Hydrogen Fluoride/Water (HF)n(H20)n (n=1,2,4) Clusters  

NASA Technical Reports Server (NTRS)

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.

Chaban, Galina M.; Gerber, R. Benny; Kwak, Dochan (Technical Monitor)

2001-01-01

151

Calculating geometric properties of three-dimensional objects from the spherical harmonic representation  

Microsoft Academic Search

The volume, location of the centroid, and second order moments of a three- dimensional star-shaped object are determined in terms of the spherical harmonic coefficients of its boundary function. Bounds on the surface area of the object are de- rived in terms of the spherical harmonic coefficients as well.Sufficient conditions under which the moments and area computed from the truncated

Artemy Baxansky; Nahum Kiryati

2007-01-01

152

Synthesis, spectroscopy (vibrational, NMR and UV-vis) studies, HOMO-LUMO and NBO analysis of 8-formyl-7-hydroxy-4-methylcoumarin by ab initio calculations  

NASA Astrophysics Data System (ADS)

In this work, 8-formyl-7-hydroxy-4-methylcoumarin has been synthesized and characterized by elemental analysis, FT-IR, FT Raman, 1H NMR, 13C NMR and UV-vis spectra. The molecular geometry, harmonic vibrational frequencies and gauge including atomic orbital (GIAO) 1H and 13C chemical shift values of the title compound in the ground state have been calculated by using Hartree-Fock (HF) and density functional methods (B3LYP) with 6-311++G(d,p) as basis set. The vibrational assignments of wave numbers were interpreted in terms of potential energy distribution (PED) analysis and the scaled B3LYP/6-311++G(d,p) results show the good agreement with the experimental values. The UV spectra of investigated compound were recorded in the region of 230-500 nm in chloroform solution. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) in gas and CHCl3 theoretically and results were compared with experimental observations. The molecular stability arising from hyperconjugative interactions and charge delocalization have been analyzed using natural bond orbital (NBO) analysis. In addition, Frontier Molecular Orbitals (FMO), Molecular Electrostatic Potential (MEP) and thermodynamic properties of the studied compound such as heat capacity (C), entropy (S) and enthalpy changes (H) at different temperatures have been calculated.

Moghanian, Hassan; Mobinikhaledi, Akbar; Monjezi, Roya

2013-11-01

153

Vibrational spectra of the steroid hormones, estradiol and estriol, calculated by density functional theory. The role of low-frequency vibrations.  

PubMed

The structure of estrogen receptors and their interaction with 17beta-estradiol and estriol are of particular interest today because the treatment of breast cancer and the cause of the disease are intricately linked to the activity of the estrogen receptor and the normal blood serum level of these hormones. Molecular geometry and vibration frequencies of these steroid hormones are calculated by density functional theory with the B3LYP/ 6-31G** approximation. Intensities of infrared absorption and Raman spectra for estradiol are in an agreement with the experiment data. The assignments of all vibrational bands in the spectra of these hormones are presented on the basis of quantum chemical calculations of frequencies and normal modes. For the large number of bands such an assignment is made for the first time. The analysis of infrared spectra of both hormones indicates some nontrivial structure-spectra correlations. A series of specific vibrations is predicted in the low-frequency region of the IR spectra; their role in hormone-receptor interaction and in energy transfer processes are discussed. The search of the optimized geometrical structure by minimization of the total energy gradient is accompanied by the second derivatives calculation; diagonalization of the Hessian matrix leads finally to solution of vibration problem. The 17beta-estradiol molecule consists of 44 atoms and has 126 normal modes of internal vibrations. All these normal modes are presented together with their analysis and comparison with experimental data. From this comparison we have obtained an assignment of all absorption IR bands of 17beta-estradiol recorded earlier in KBr. For all stretching vibrations our assignment is in agreement with the previous one, obtained on the basis of the empirical rules. Direct DFT calculation of vibrational frequencies cannot provide a 100% agreement with the experimental IR spectra and scaling factors in the range of 0.95-0.97 are used in order to fit theoretical and experimental data. PMID:19140454

Minaeva, V A; Minaev, B F; Hovorun, D M

2008-01-01

154

Isotope effects on nuclear magnetic shieldings calculated by including zero-point vibration corrections: the VMF approach  

NASA Astrophysics Data System (ADS)

As a minimal dynamic correction the 'zero-point vibration', ZPV, was included in the ab initio calculation of the isotropic magnetic shielding of 13C, 19F, 29Si, 31P, and 35Cl in some molecules including the references of NMR spectroscopy (f.i. CFCl 3, CH 3-NO 2, and TMS). In contrast to most previous works the ZPV correction is not based on gradients of internal coordinates, but uses derivatives obtained by 'vibration mode following' (VMF, the coordinates of the gradients describing the magnetic shielding hypersurface are the normal coordinates of the ground state vibration motion). The vibrational corrections obtained at the applied DFT level of theory are slightly smaller than those reported for MP2 calculations. Isotope effects computed with the ZPV/VMF correction are in reasonable agreement with experimental data. Contributions from individual vibration modes to the zero-point correction show that rotational motions have a large effect.

Dransfeld, Alk

2004-03-01

155

Ab Initio and Improved Empirical Potentials for the Calculation of the Anharmonic Vibrational States and Intramolecular Mode Coupling of N-Methylacetamide  

NASA Technical Reports Server (NTRS)

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.

Gregurick, Susan K.; Chaban, Galina M.; Gerber, R. Benny; Kwak, Dochou (Technical Monitor)

2001-01-01

156

Exploring the effect of anharmonicity of molecular vibrations on thermodynamic properties  

NASA Astrophysics Data System (ADS)

Thermodynamic properties of selected small and medium size molecules were calculated using harmonic and anharmonic vibrational frequencies. Harmonic vibrational frequencies were obtained by normal mode analysis, whereas anharmonic ones were calculated using the vibrational self-consistent field (VSCF) method. The calculated and available experimental thermodynamic data for zero point energy, enthalpy, entropy, and heat capacity are compared. It is found that the anharmonicity and coupling of molecular vibrations can play a significant role in predicting accurate thermodynamic quantities. Limitations of the current VSCF method for low frequency modes have been partially removed by following normal mode displacements in internal, rather than Cartesian, coordinates.

Njegic, Bosiljka; Gordon, Mark S.

2006-12-01

157

Exploring the effect of anharmonicity of molecular vibrations on thermodynamic properties.  

PubMed

Thermodynamic properties of selected small and medium size molecules were calculated using harmonic and anharmonic vibrational frequencies. Harmonic vibrational frequencies were obtained by normal mode analysis, whereas anharmonic ones were calculated using the vibrational self-consistent field (VSCF) method. The calculated and available experimental thermodynamic data for zero point energy, enthalpy, entropy, and heat capacity are compared. It is found that the anharmonicity and coupling of molecular vibrations can play a significant role in predicting accurate thermodynamic quantities. Limitations of the current VSCF method for low frequency modes have been partially removed by following normal mode displacements in internal, rather than Cartesian, coordinates. PMID:17176129

Njegic, Bosiljka; Gordon, Mark S

2006-12-14

158

Fast vibrational calculation of anharmonic OH-stretch frequencies for two low-energy noradrenaline conformers.  

PubMed

We introduce a new reduced-coupling technique to accelerate direct calculations of a selected number of vibrational frequencies in large molecular systems. Our method combines the advantages of the single-to-all correlation-corrected vibrational self-consistent field (STA-CC-VSCF) approach [D. M. Benoit, J. Chem. Phys. 125, 244110 (2006)] with those of the fast-CC-VSCF technique [D. M. Benoit, J. Chem. Phys. 120, 562 (2004)] and allows the ab initio calculation of only the relevant parts of the required potential energy surface (PES). We demonstrate, using a set of five aliphatic alcohol molecules, that the new fast-STA-CC-VSCF method is accurate and leads to very substantial time gains for the computations of the PES. We then use the fast-STA-CC-VSCF method to accelerate the computation of the OH-stretch and NH-stretch frequencies of the two lowest-energy conformers of noradrenaline, namely, AG1a and GG1a. Our new approach enables us to run the calculation 89 times faster than the standard CC-VSCF technique and makes it possible to use a high-level MP2/TZP description of the PES. We demonstrate that the influence of the strong mode-mode couplings is crucial for a realistic description of the particular OH-stretch vibrational signature of each conformer. Finally, of the two possible low-energy conformers, we identify AG1a as the one most likely to have been observed in the experiments of Snoek et al. [Mol. Phys. 101, 1239 (2003)]. PMID:19102529

Benoit, David M

2008-12-21

159

Structural, elastic, vibrational and electronic properties of amorphous Al2O3 from ab initio calculations.  

PubMed

First-principles molecular dynamics calculations of the structural, elastic, vibrational and electronic properties of amorphous Al(2)O(3), in a system consisting of a supercell of 80 atoms, are reported. A detailed analysis of the interatomic correlations allows us to conclude that the short-range order is mainly composed of AlO(4) tetrahedra, but, in contrast with previous results, also an important number of AlO(6) octahedra and AlO(5) units are present. The vibrational density of states presents two frequency bands, related to bond-bending and bond-stretching modes. It also shows other recognizable features present in similar amorphous oxides. We also present the calculation of elastic properties (bulk modulus and shear modulus). The calculated electronic structure of the material, including total and partial electronic density of states, charge distribution, electron localization function and the ionicity for each species, gives evidence of correlation between the ionicity and the coordination for each Al atom. PMID:22101197

Davis, Sergio; Gutiérrez, Gonzalo

2011-12-14

160

Vibrational spectroscopic (FTIR and FT-Raman), first-order hyperpolarizablity, HOMO, LUMO, NBO, Mulliken charge analyses of 2-ethylimidazole based on Hartree-Fock and DFT calculations  

NASA Astrophysics Data System (ADS)

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.

Arivazhagan, M.; Manivel, S.; Jeyavijayan, S.; Meenakshi, R.

2015-01-01

161

Vibrational spectroscopic (FTIR and FT-Raman), first-order hyperpolarizablity, HOMO, LUMO, NBO, Mulliken charge analyses of 2-ethylimidazole based on Hartree-Fock and DFT calculations.  

PubMed

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. PMID:25048284

Arivazhagan, M; Manivel, S; Jeyavijayan, S; Meenakshi, R

2015-01-01

162

A complete vibrational study on a potential environmental toxicant agent, the 3,3?,4,4?-tetrachloroazobenzene combining the FTIR, FTRaman, UV-Visible and NMR spectroscopies with DFT calculations  

NASA Astrophysics Data System (ADS)

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 1H and 13C chemicals shifts are in good conformity with the corresponding experimental NMR spectra of TCAB in solution. The np®p* 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.

Castillo, María V.; Pergomet, Jorgelina L.; Carnavale, Gustavo A.; Davies, Lilian; Zinczuk, Juan; Brandán, Silvia A.

2015-01-01

163

Structural, vibrational, NLO, MEP, NBO analysis and DFT calculation of bis 2,5-dimethylanilinium sulfate  

NASA Astrophysics Data System (ADS)

A new organic-inorganic salt, bis 2,5-dimethylanilinium sulfate has been synthesized by slow evaporation method at room temperature and characterized by single X-ray diffraction, FT-IR and FT-Raman spectroscopies. The optimized molecular structure, vibrational wavenumbers, atomic charges, molecular electrostatic potential, NBO, NLO and electronic properties were calculated by the density functional theory (DFT) method using the B3LYP function with the 6-31G(d,p) basis set. The complete assignments of the vibrational spectra were carried out with the aid of potential energy distribution (PED). Simulation of infrared and Raman spectra led to excellent overall agreement with the observed spectral patterns. The stability and charge delocalization of the molecule were studied by natural bond orbital (NBO) analysis. In addition, a molecular electrostatic potential map (MEP) of the title compound has been analyzed for predicting the reactive sites. NLO properties and Mulliken charges were also calculated and interpreted. The lowering in the HOMO and LUMO energy gap explains the eventual charge transfer interactions that take place within the molecules.

Guidara, Sameh; Feki, Habib; Abid, Younes

2015-01-01

164

Vibrational spectra of light and heavy water with application to neutron cross section calculations  

SciTech Connect

The design of nuclear reactors and neutron moderators require a good representation of the interaction of low energy (E < 1 eV) neutrons with hydrogen and deuterium containing materials. These models are based on the dynamics of the material, represented by its vibrational spectrum. In this paper, we show calculations of the frequency spectrum for light and heavy water at room temperature using two flexible point charge potentials: SPC-MPG and TIP4P/2005f. The results are compared with experimental measurements, with emphasis on inelastic neutron scattering data. Finally, the resulting spectra are applied to calculation of neutron scattering cross sections for these materials, which were found to be a significant improvement over library data.

Damian, J. I. Marquez; Granada, J. R. [Neutron Physics Department and Instituto Balseiro, Centro Atomico Bariloche, CNEA (Argentina); Malaspina, D. C. [Department of Biomedical Engineering and Chemistry of Life Processes Institute, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208 (United States)

2013-07-14

165

Modeling and active vibration suppression of a single-walled carbon nanotube subjected to a moving harmonic load based on a nonlocal elasticity theory  

NASA Astrophysics Data System (ADS)

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.

Pirmohammadi, A. A.; Pourseifi, M.; Rahmani, O.; Hoseini, S. A. H.

2014-07-01

166

Nuclear magnetic resonance, vibrational spectroscopic studies, physico-chemical properties and computational calculations on (nitrophenyl) octahydroquinolindiones by DFT method  

NASA Astrophysics Data System (ADS)

In the present study, 2?-nitrophenyloctahydroquinolinedione and its 3?-nitrophenyl isomer were synthesized and characterized by FT-IR, FT-Raman, 1H NMR and 13C NMR spectroscopy. The molecular geometry, vibrational frequencies, 1H and 13C 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 1H and 13C NMR were calculated using gauge-invariant atomic orbital (GIAO) method. The experimental vibrational frequencies, 1H and 13C 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.

Pasha, M. A.; Siddekha, Aisha; Mishra, Soni; Azzam, Sadeq Hamood Saleh; Umapathy, S.

2015-02-01

167

Bond-charge-model calculation of vibrational properties in small carbon aggregates: From spherical clusters to linear chains  

NASA Astrophysics Data System (ADS)

The bond-charge model, originally devised to calculate the phonon spectrum of bulk semiconductors and extended with success to describe the vibrations of graphite and fullerenes C60 and C70, is applied to calculate the normal modes of vibration of small carbon aggregates, as the smallest fullerene (C20), and odd-numbered linear and cyclic Cn clusters (n=5-19). The resulting spectra provide a satisfactory account of the experimental findings and are in overall agreement with the results of ab initio calculations.

Breda, Nicola; Onida, Giovanni; Benedek, Giorgio; Colò, Gianluca; Broglia, Ricardo A.

1998-10-01

168

The vibrational energies of ozone up to the dissociation threshold: Dynamics calculations on an accurate potential energy surface  

E-print Network

The vibrational energies of ozone up to the dissociation threshold: Dynamics calculations present an ab initio potential energy surface for the ground electronic state of ozone. It is global, i. All bound states of nonrotating ozone up to more than 99% of the dissociation energy are calculated

Farantos, Stavros C.

169

Vinylphosphine-borane: synthesis, gas phase infrared spectroscopy, and quantum chemical vibrational calculations.  

PubMed

Both experimental and theoretical investigations are reported on the infrared spectrum of vinylphosphine-borane (CH(2)=CHPH(2) x BH(3)), a donor-acceptor complex. The gas phase infrared spectra (3500-600 cm(-1)) have been recorded at 0.5 cm(-1) resolution. This first primary alpha,beta-unsaturated phosphine-borane synthesized up to now is kinetically very unstable in the gas phase and decomposes rapidly into two fragments: the free vinylphosphine CH(2)=CHPH(2) and the monoborane BH(3) which dimerizes to form the more stable diborane B(2)H(6). Spectra of free CH(2)=CHPH(2) and B(2)H(6) compounds were also recorded to assign some vibration modes of the complex in very dense spectral regions. The analysis was completed by carrying out quantum mechanical calculations by density functional theory method at the B3LYP/6-31+G(**) level. Anharmonic frequencies and infrared intensities of the two predicted gauche and syn conformers of the vinylphosphine-borane complex were calculated in the 3500-100 cm(-1) region with the use of a variational approach, implemented in the P_ANHAR_V1.2 code. Because of the relatively weak interaction between the vinylphosphine and the monoborane, the vibrations of the complex can easily be subdivided into modes localized in the CH(2)=CHPH(2) and BH(3) moieties and into "intermolecular" modes. Localized modes are unambiguously correlated with the modes of the isolated monomers. Therefore, they are described in terms of the monomer vibrations, and the complexation shifts are defined as Delta nu = nu(complex) - nu(monomer) to make the effect of the complexation precise on each localized mode. In this objective, anharmonic frequencies and infrared intensities of the BH(3) monomer and the stable gauche and syn conformers of the free vinylphosphine were obtained at the same level of theory. In the gas phase, only the syn form of the complex was observed and assigned. All theoretically predicted frequencies and complexation shifts in magnitude and direction are in good agreement with experiment. By infrared spectroscopy assisted by quantum chemical calculations, the consequences of the complexation of an alpha,beta-unsaturated phosphine by borane on the physicochemical properties of the formed 12-atom complex have been efficiently evaluated. PMID:19071917

Khater, Brahim; Guillemin, Jean-Claude; Benidar, Abdessamad; Bégué, Didier; Pouchan, Claude

2008-12-14

170

Vinylphosphine-borane: Synthesis, gas phase infrared spectroscopy, and quantum chemical vibrational calculations  

NASA Astrophysics Data System (ADS)

Both experimental and theoretical investigations are reported on the infrared spectrum of vinylphosphine-borane (CH2=CHPH2?BH3), a donor-acceptor complex. The gas phase infrared spectra (3500-600 cm-1) have been recorded at 0.5 cm-1 resolution. This first primary ?,?-unsaturated phosphine-borane synthesized up to now is kinetically very unstable in the gas phase and decomposes rapidly into two fragments: the free vinylphosphine CH2=CHPH2 and the monoborane BH3 which dimerizes to form the more stable diborane B2H6. Spectra of free CH2=CHPH2 and B2H6 compounds were also recorded to assign some vibration modes of the complex in very dense spectral regions. The analysis was completed by carrying out quantum mechanical calculations by density functional theory method at the B3LYP/6-31+G?? level. Anharmonic frequencies and infrared intensities of the two predicted gauche and syn conformers of the vinylphosphine-borane complex were calculated in the 3500-100 cm-1 region with the use of a variational approach, implemented in the P_ANHAR_V1.2 code. Because of the relatively weak interaction between the vinylphosphine and the monoborane, the vibrations of the complex can easily be subdivided into modes localized in the CH2=CHPH2 and BH3 moieties and into "intermolecular" modes. Localized modes are unambiguously correlated with the modes of the isolated monomers. Therefore, they are described in terms of the monomer vibrations, and the complexation shifts are defined as ??=?complex-?monomer to make the effect of the complexation precise on each localized mode. In this objective, anharmonic frequencies and infrared intensities of the BH3 monomer and the stable gauche and syn conformers of the free vinylphosphine were obtained at the same level of theory. In the gas phase, only the syn form of the complex was observed and assigned. All theoretically predicted frequencies and complexation shifts in magnitude and direction are in good agreement with experiment. By infrared spectroscopy assisted by quantum chemical calculations, the consequences of the complexation of an ?,?-unsaturated phosphine by borane on the physicochemical properties of the formed 12-atom complex have been efficiently evaluated.

Khater, Brahim; Guillemin, Jean-Claude; Benidar, Abdessamad; Bégué, Didier; Pouchan, Claude

2008-12-01

171

Structural and vibrational study of primidone based on monomer and dimer calculations.  

PubMed

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

Celik, Sefa; Kecel-Gunduz, Serda; Ozel, Aysen E; Akyuz, Sevim

2015-04-01

172

Vibrationally excited states of DC 5N: Millimeter-wave spectroscopy and coupled cluster calculations  

NASA Astrophysics Data System (ADS)

The rotational spectrum of DC 5N has been investigated in the millimeter-wave region for 16 vibrationally excited states which approximately lie below 760 cm -1, namely ( v6v7v8v9v10v11)=(000001), (000002), (000003), (000005), (000010), (000020), (000100) (001000), (010000), (100000), (000011), (000101), (001001), (010001), (001010), and (010010). Gas-phase copyrolysis of fully deuterated pyridine and phosphorus trichloride was used to produce the semi-stable DC 5N molecule. In addition to the usual l-type resonances, several vibrational interactions have been taken into account to fit properly the measured transition frequencies. The most important perturbations are caused by the cubic anharmonic interactions which mix the v6 stretching state with the 2 v10 overtone and the v8+ v11 and v7+ v11 bending combination states. The analysis of the spectra was facilitated by theoretical predictions from CCSD(T) calculations with the cc-pVQZ basis.

Bizzocchi, L.; Degli Esposti, C.; Botschwina, P.

2006-01-01

173

DFT calculations of 2,6-dimethylpyrazine (26DMP) and its complex with chloranilic acid (CLA): Comparison to INS, IR and Raman vibration spectra  

NASA Astrophysics Data System (ADS)

The inelastic neutron scattering (INS), infrared and Raman spectra of crystalline 2,6-dimethylpyrazine (26DMP) and its complex with chloranilic acid (26DMP·CLA) were measured. Simultaneously the DFT calculations of the molecular structures and frequencies of the normal vibrations were performed by using various functionals. The INS spectra were simulated in the energy range up to 1200 cm -1, on the basis of the calculated frequencies. A very good conformity was obtained between experimental and calculated data with respect to the structure as well as to frequencies, with exception, however, of the CH 3 torsional modes. The structural analysis based on the deviation from the sum of the van der Waals radii showed that the packing of the methyl groups in the 26DMP·CLA complex was markedly stronger than that in the neat 26DMP. However, the DFT calculations overestimated the role of this effect that may be due to a limitation of the applied methods. In addition the anharmonicity of the rotational potential led to the librational energies different from those obtained using a harmonic potential.

Pawlukoj?, A.; Sobczyk, L.; Prager, M.; Bator, G.; Grech, E.; Nowicka-Scheibe, J.

2008-12-01

174

A comparison of several methods for the calculation of vibration mode shape derivatives  

NASA Technical Reports Server (NTRS)

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.

Sutter, T. R.; Camarda, C. J.; Walsh, J. L.; Adelman, H. M.

1986-01-01

175

Calculation of electronic, structural, and vibrational properties in alkali halides using a density-functional method with localized densities  

NASA Astrophysics Data System (ADS)

A recently developed density-functional method based on localized densities is applied to calculate electronic, structural, and vibrational properties of 20 alkali halides with elements lithium through cesium and fluorine through iodine. Properties calculated include dissociation energy, lattice parameter, dielectric constant, elastic moduli, and phonon frequencies for the high-symmetry points of the Brillouin zone. Results are discussed and compared with experiment and other calculations.

Mei, W. N.; Boyer, L. L.; Mehl, M. J.; Ossowski, M. M.; Stokes, H. T.

2000-05-01

176

Effects of broad-banded higher harmonics on fatigue damage of risers due to vortex-induced vibrations  

E-print Network

Recent works have discussed "chaotic" or "Type-II" riser motion and suggested that it is a general feature of VIV riser response. Chaotic riser response contains broad-banded harmonics and a combination of standing and ...

Price, Rachel Elizabeth

2011-01-01

177

Calculation of the Vibrational Stark Effect Using a First-Principles QM/MM Approach.  

PubMed

The proper description of the electric environment of condensed phases is a critical challenge for force field methods. To test and validate the ability of the CHARMM additive force field to describe the electric environment in aqueous solution combined QM/MM calculations have been used to calculate the vibrational Stark effect (VSE). We utilized a first principles methodology using correlated electronic structure techniques to compute the Stark shift between the gas phase and solvent environments and between two different solvent environments of three VSE probes containing acetonitrile or fluorine functionalities which have been well-characterized experimentally. Reasonable agreement with the experimentally determined Stark shifts is obtained when the MM atoms are described by the CHARMM additive force field, though it is essential to employ an anharmonic correction in the frequency calculation. In addition, the electric field created by the solvent is computed along the CN bond and a theoretical Stark tuning rate is determined for acetonitrile and shown to be in satisfactory agreement with experiment. PMID:21423871

Ringer, Ashley L; Mackerell, Alexander D

2011-02-21

178

Homogeneous and mixed UF6 clusters with Ar: Calculations of structures and vibrational spectra  

NASA Astrophysics Data System (ADS)

A recently developed site-site intermolecular potential for UF6, featuring exchange, dispersion, and electrostatic terms, is used to calculate minimum energy structures of homogeneous UF6 clusters up to the decamer. The structures of mixed (UF6)2-Arn clusters are also calculated by adding appropriate interaction terms. The IR spectra corresponding to the determined cluster structures in the region of the ?3 vibrational mode of the monomer (at 627.724 cm-1) are calculated using a second-order line shift formalism, treating the anharmonic intramolecular force field and the intermolecular potential as a perturbation. The leading interaction mechanism responsible for the line shifts of the ?3 mode is found to be the electrostatic one (implicitly the resonant dipole-dipole coupling). The theoretical spectra are shown to satisfactorily describe the peaks around 623, 632, and 640 cm-1 found in the recently measured Fourier transform IR spectra in a continuous supersonic Laval nozzle flow and attributed to the clusters formed by UF6.

Beu, T. A.; Onoe, J.; Takeuchi, K.

1998-11-01

179

Vibrational analysis of the n-paraffins—II. Normal co-ordinate calculations  

NASA Astrophysics Data System (ADS)

Extensive normal co-ordinate calculations on the extended n-paraffins C 2H 6 through n-C 14H 30 and polyethylene have been carried out using a perturbation method programmed for the IBM 7090 which adjusts force constants for any number of molecules simultaneously. Our ability to fit some 270 fundamental frequencies to their observed values with an average error of 0-25 per cent lends strong support to our interpretation of the vibrational spectra of the n-paraffins. Our confidence in the correctness of our interpretation for the n-paraffins extends to polyethylene, whose spectrum we believe is now correctly assigned. These calculations have also led to normal co-ordinates and a thirty-five parameter valence force field for the n-paraffins. The valence force field has been compared to a Urey-Bradley force field derived from the same molecules, and some shortcomings of the Urey-Bradley field are apparent. Transferability of the force constants among the n-paraffins is excellent. The success of a calculation in which isobutane and neopentane were included with the n-paraffins suggests that this transferability may also extend to branched hydrocarbons.

Schachtschneider, J. H.; Snyder, R. G.

1989-01-01

180

Vibrational spectra, DFT calculations, and conformations of 5?-chloro-1-isopropyl-7-azaindirubin-3?-oxime  

NASA Astrophysics Data System (ADS)

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.

Robbins, Timothy J.; Wang, Yongmei; Yao, Qi-Zheng; Wang, Zhao-Hui; Cheng, Jingcai; Li, Ying-Sing

2013-09-01

181

First-principles calculations on the electronic, vibrational, and optical properties of semiconductor nanowires  

NASA Astrophysics Data System (ADS)

The semiconductor nanowire (NW) has attracted significant attention as a new one-dimensional structure for fundamental studies and also as a potential building block for nanodevices. When the size of NWs becomes close to the order of the de Broglie wavelength of electrons, the quantum confinement effect significantly affects the electronic behaviors of NWs and raises expectations for many novel applications in microelectronics. As the technology advances, more and more fine semiconductor NWs are fabricated in the laboratories, which provide good platforms to study the special properties of low-dimensional systems. From these new nanostructures, we choose to study the single crystal silicon nanowire (SiNW). One advantage of this choice of SiNWs is that we have the solid and complete knowledge about the electronic structure of bulk silicon, which provides valuable information for us to understand the quantum confinement effect in SiNWs. The other reason for this choice is that the silicon-based technology is so highly developed that scientists prefer silicon as the elementary material for the cost consideration, even it may not be the highest performance candidate. Therefore, our calculations on SiNWs should be useful for the industrial development of today's nanotechnology. As a starting point, we begin by studying the ground electronic state of SiNWs and performing calculations on the following three physical properties. Based on thorough knowledge about the ground state of electrons, the first part of our work is to calculate the properties of lattice vibrations of SiNWs. The density functional theory (DFT) based linear-response method is used to obtain lattice vibrational modes. We plot the density of vibrational modes at the Gamma point of the Brillouin zone and show a clear evolutionary from bulk silicon to the narrow SiNW. Two kinds of frequency shifts of lattice vibrational modes are found: One is the red shift of the optical modes, the other is the blue shift of the radial breathing modes (RBMs). We discover that the size dependence of the frequency shifts of RBMs can be described well by the elastic model with the cylindrical boundary confinement. In order to characterize these confined modes in SiNWs, we calculate the first-order Raman activities of the smallest SiNW, and find that the RBM is strongly active in the scattering spectrum. Therefore, our calculated result about the size dependence of the frequency of RBM provides an easy way to estimate the size of the nanowires from the corresponding Raman spectrum. The excited-state properties of nanostructures are of critical importance in the design of functional optical devices. The low dimensionality and reduced size tend to strengthen the effective Coulomb interaction in nanostructures. Quantitative evaluations of physical properties manifesting this effect are therefore timely and valuable to the nanotechnology research. In the second part of my work, we focus on the correlated electron-hole states in semiconductor NWs and their influence on the optical absorption spectrum. First-principles calculations are performed for an isolated hydrogen-passivated SiNW with a diameter of 1.2 nm. By using plane waves and pseudopotentials, the quasiparticle states are calculated within the many-body perturbation theory with the so-called GW approximation, and the electron-hole interaction is evaluated with the Bethe-Salpeter equation (BSE). The enhanced Coulomb interaction in this confined system results in an unusually large shift (1-2 eV) of the optical spectrum as well as a significant increase in certain absorption peak intensity. The current results predict anomalous excited-state properties in semiconductor NWs that may impact future applications of these nanostructures. In the third part of my work, the electronic band structures of Si/Ge core-shell NWs are studied with first-principles calculations. The electronic states close to the band gap of NWs along the [110] direction are found to be confined within the core and the shell, respectively. Our calculated resul

Yang, Li

182

Variational calculations of rotational-vibrational energies of CH{sub 4} and isotopomers using an adjusted ab initio potential  

SciTech Connect

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.

Carter, S.; Bowman, J.M.

2000-03-23

183

The molecular structures, vibrational spectroscopies (FT-IR and Raman) and quantum chemical calculations of n-alkyltrimethylammonium bromides  

NASA Astrophysics Data System (ADS)

The FT-IR and micro-Raman spectra of three n-alkyltrimethylammonium bromides (dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and hexadecyl(cetyl)trimethylammonium bromide (CTAB)) in powder form were recorded in the regions 4000-550 cm-1 and 3200-300 cm-1, respectively. The optimized geometries and vibrational frequencies of DTAB, TTAB and CTAB have been carried out with ab initio Hartree-Fock (HF) and density functional theory method B3LYP calculations with the 6-31 G (d, p) basis set in the ground state. The comparison of the observed fundamental vibrational frequencies and calculated results for the fundamental vibrational frequencies of DTAB, TTAB and CTAB indicate that the scaled B3LYP method is superior compared to the scaled HF method.

Gökce, Halil; Bahçeli, Semiha

2013-11-01

184

Calculated Dependence of Vibrational Band Frequencies of Single-Walled Carbon Nanotubes on Diameter  

NASA Astrophysics Data System (ADS)

We have used density functional theory (DFT) at the B3LYP/6-31G level to calculate Raman and IR spectra of the fourteen zigzag (n, 0) single-walled carbon nanotubes (SWCNTs) and (n, 0)&(2n, 0) double walled carbon nanotube (DWCNTs) that have n ranging from 6 to 19 for SWCNTS, n = 6 to 8 for DWCNTs. In the low frequency RBM region, calculated Raman spectra of SWCNTs indicated that there are three vibrational modes, of symmetries A{_1g}, E{_1g} and E{_2g}, whose frequencies depend strongly on nanotube diameter. The E{_2g} g mode is not only diameter dependent, but also the even and odd number hexagon formed in the circumference direction of the CNTs. There are also two IR spectral modes (of A2u and E1u symmetries) found in calculated IR spectra with strong diameter dependencies. We have also found three Raman bands with E{_1g}, A{_1g} and E{_2g} symmetries to exist in the G-band region. For this latter case, computed spectra indicated that while Raman bands with A1g symmetry essentially remain constant for the even number hexagon formed in the circumference direction ((0, 2n)-type CNTs; with band position 1526 61617; 0.5 cm^{-1}), but that for (0, 2n+1)-type CNTs are diameter dependent. The frequencies of the E{_1g} and E{_2g} modes (in the G-band region) are not only strongly diameter dependent, but also expected to converge towards one another with increasing tube diameter. This latter type of behavior can lead to erroneous classification of nanotubes as metallic or semiconducting, since partially overlapping bands in the G-band region might result in bands with diffuse shoulder, a characteristic of metallic SWCNTs. The RBMs for DWCNTs are also strongly diameter dependent and are blue shifted reference to their corresponding RBMs in the spectra of SWCNTs. The relative distance between RBMs vibrational modes in the spectrum of a desired DWCNT is larger than that for the corresponding SWCNTs. The electron density for the small sized DWCNT, (6,0)&(12,0), indicated an intertube CC chemical bonding in the excite state.

Aydin, Metin; Akins, Daniel L.

2009-06-01

185

pH-dependent Raman study of pyrrole and its vibrational analysis using DFT calculations  

NASA Astrophysics Data System (ADS)

Raman spectra of pyrrole in aqueous medium at different pH values, 2.5, 5.5, 7.5 and 10.5 were recorded in the two spectral regions, 1040-1160 cm -1 and 3300-3360 cm -1 and pH dependence of the linewidth, peak position and intensity of the Raman bands corresponding to the ring breathing and symmetric ?(N-H) stretching modes were examined. A linear pH dependence of the peak positions for the ring breathing mode and a maximum at nearly neutral pH (7.5) for the symmetric ?(N-H) normal mode is observed, whereas the linewidth (FWHM) shows almost no variation with the change of pH. A slight decrease in the wavenumber position of the ?(N-H) mode at pH value >7.5 indicates that the influence of deprotonation is small, which results from a weak interaction between the reference molecule and the surrounding environment. The density functional theory (DFT) calculations were made primarily to obtain the optimized geometry and vibrational spectra of pyrrole in the ground electronic state using B3LYP functional and the highest level basis set 6-311++G(d,p). The assignments of the normal modes of pyrrole were made on the basis of potential energy distribution (PED). The calculations were also performed on protonated and deprotonated structures of pyrrole.

Singh, Dheeraj K.; Srivastava, Sunil K.; Ojha, Animesh K.; Asthana, B. P.

2008-12-01

186

Orbital-optimized coupled-electron pair theory and its analytic gradients: Accurate equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions  

NASA Astrophysics Data System (ADS)

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(N6) 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 Å 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.

Bozkaya, U?ur; Sherrill, C. David

2013-08-01

187

Orbital-optimized coupled-electron pair theory and its analytic gradients: accurate equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions.  

PubMed

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

Bozkaya, U?ur; Sherrill, C David

2013-08-01

188

Secondary development of ANSYS and its application in calculating the natural vibration period of variable cross-section towers  

Microsoft Academic Search

Method of discount quality is always used in ing the natural vibration period of tower in the design of tower. When tower's cross-section is variable, the calculating formula is complex, and big workload. Thus, this method is cramped in actual engineering. In view of the powerful function of ANSYS, the secondary development of ANSYS is worked with the me­ thod

Guo Yi; Wen Huabin; Zhong Xiaofeng; Tang Kelun; Hu Guangzhong

2011-01-01

189

A band Lanczos approach for calculation of vibrational coupled cluster response functions: simultaneous calculation of IR and Raman anharmonic spectra for the complex of pyridine and a silver cation.  

PubMed

We describe new methods for the calculation of IR and Raman spectra using vibrational response theory. Using damped linear response functions that incorporate a Lorentzian line-shape function from the outset, it is shown how the calculation of Raman spectra can be carried out through the calculation of a set of vibrational response functions in the same manner as described previously for IR spectra. The necessary set of response functions can be calculated for both vibrational coupled cluster (VCC) and vibrational configuration interaction (VCI) anharmonic vibrational wave-functions. For the efficient and simultaneous calculation of the full set of necessary response functions, a non-hermitian band Lanczos algorithm is implemented for VCC, and a hermitian band Lanczos algorithm is implemented for VCI. It is shown that the simultaneous calculation of several response functions is often advantageous. Sample calculations are presented for pyridine and the complex between pyridine and the silver cation. PMID:23609967

Godtliebsen, Ian H; Christiansen, Ove

2013-07-01

190

VOLUME 81, NUMBER 1 P H Y S I C A L R E V I E W L E T T E R S 6 JULY 1998 Harmonic Vibrational Excitations in Disordered Solids and the "Boson Peak"  

E-print Network

VOLUME 81, NUMBER 1 P H Y S I C A L R E V I E W L E T T E R S 6 JULY 1998 Harmonic Vibrational Excitations in Disordered Solids and the "Boson Peak" Walter Schirmacher Physik-Department E13, Technische

Schirmacher, Walter

191

Direct calculations of vibrational absorption and circular dichroism spectra of alanine dipeptide analog in water: Quantum mechanical\\/molecular mechanical molecular dynamics simulations  

Microsoft Academic Search

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

Seongeun Yang; Minhaeng Cho

2009-01-01

192

Nonperturbative quantum and classical calculations of multiphoton vibrational excitation and dissociation of Morse molecules^1  

NASA Astrophysics Data System (ADS)

The multiphoton vibrational excitation and dissociation of Morse molecules have been computed nonperturbatively using Hamilton's and Schr?dinger's time-dependent equations, for a range of laser pulse parameters. The time-dependent Schr?dinger equation is solved by the state-specific expansion approach [e.g.,1]. For its solution, emphasis has been given on the inclusion of the continuous spectrum, whose contribution to the multiphoton probabilities for resonance excitation to a number of excited discrete states as well as to dissociation has been examined as a function of laser intensity, frequency and pulse duration. An analysis of possible quantal-classical correspondences for this system is being carried out. We note that distinct features exist from previous classical calculations [2]. For example, the dependence on the laser frequency gives rise to an asymmetry around the red-shifted frequency corresponding to the maximum probability. [1] Th. Mercouris, I. D. Petsalakis and C. A. Nicolaides, J. Phys. B 27, L519 (1994). [2] V. Constantoudis and C. A. Nicolaides, Phys. Rev. E 64, 562112 (2001). ^1This work was supported by the program 'Pythagoras' which is co - funded by the European Social Fund (75%) and Natl. Resources (25%). ^2Physics Department, National Technical University, Athens, Greece.^3Theoretical and Physical Chemistry Institute, Hellenic Research Foundation, Athens, Greece.

Dimitriou, K. I.; Mercouris, Th.; Constantoudis, V.; Komninos, Y.; Nicolaides, C. A.

2006-05-01

193

Predictive calculation of the lattice thermal conductivity with temperature-dependent vibrational parameters  

NASA Astrophysics Data System (ADS)

This paper presents a predictive model for the lattice thermal conductivity. The model is based on Callaway's solution to the Boltzmann equation for phonons which discriminates between the natures of the resistive and nonresistive phonon processes. However, the present model uses temperature-dependent lattice vibrational parameters and sound group velocities calculated on the basis of a dynamical matrix. No adjustment to thermal conductivity measurements is required. The model requires only the material mechanical properties as inputs to yield the material thermal conductivity as a function of temperature. A precise transmission probability function is introduced in the model in order to widen its application for the cases where interfaces are present. The importance of all the features of the developed model is demonstrated clearly with reference to reported data regarding the effects of surface orientation and isotope composition in single crystals, the effect of alloy composition in alloys, and the effect of grains boundaries in polycrystals. Namely, the developed model accounts for (i) the effects of surface orientation and isotope composition on the thermal conductivity of silicon and germanium single crystals, (ii) the effect of alloy composition on the thermal conductivity of silicon-germanium alloys, and (iii) the effect of phonon scattering at grains boundaries on the thermal conductivity of polycrystalline silicon.

Alameh, Z.; Kazan, M.

2012-12-01

194

Crystal and molecular structure of N-(4-nitrophenyl)-?-alanine—Its vibrational spectra and theoretical calculations  

NASA Astrophysics Data System (ADS)

The N-(4-nitrophenyl)-?-alanine in crystalline form directly by the addition of 4-nitroaniline to the acrylic acid in aqueous solution has been obtained. The title ?-alanine derivative crystallizes in the P2 1/ c space group of monoclinic system with four molecules per unit cell. The X-ray geometry of ?-alanine derivative molecule has been compared with those obtained by molecular orbital calculations corresponding to the gas phase. In the crystal the molecules related by an inversion center interact via symmetrically equivalent O-H⋯O hydrogen bonds with O⋯O distance of 2.656(2) Å forming a dimeric structure. The dimers of ?-alanine derivative weakly interact via N-H⋯O hydrogen bonds between the H atom of ?-amine groups and one of O atom of nitro groups. The room temperature powder vibrational (infrared and Raman) measurements are in accordance with the X-ray analysis. In aqueous solution of 4-nitroaniline and acrylic acid, the double C dbnd C bond of vinyl group of acrylic acid breaks as result of 4-nitroaniline addition.

Marchewka, M. K.; Drozd, M.; Janczak, J.

2011-08-01

195

Voids at the tunnel–soil interface for calculation of ground vibration from underground railways  

Microsoft Academic Search

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

Simon Jones; Hugh Hunt

2011-01-01

196

Two-dimensional vibrational spectroscopy. I. Theoretical calculation of the nonlinear Raman response function of CHCl3  

NASA Astrophysics Data System (ADS)

The two-dimensional Raman response function of CHCl3 is theoretically considered with interpretations of each peak in terms of the associated vibrational transition pathways. In order to numerically calculate the 2D Raman spectrum, ab initio calculations of necessary quantities, such as the first- and second-order derivatives of the molecular polarizability with respect to vibrational coordinates and cubic potential anharmonic coefficients, were carried out by using the basis set 6-311++G(2df,2pd) at the Hartree-Fock level. Quantitative comparison between the two nonlinear response functions associated with the mechanical and electronic anharmonicities shows that the 2D Raman response from the high-frequency intramolecular vibrational modes of CHCl3 is mainly determined by the mechanical (potential) anharmonicity contributions. On the other hand, it is found that the two distinctive contributions originating from the mechanical and electronic anharmonicities interfere in the low-frequency region of the 2D spectrum. Overall, it is suggested that the high-frequency 2D Raman spectrum could provide a map of the mechanical anharmonic mode couplings. We briefly discuss how the 2D Raman spectrum can be used to elucidate the potential energy hypersurface and in turn to study the intramolecular vibrational energy redistribution process.

Hahn, Sangjoon; Park, Kisam; Cho, Minhaeng

1999-09-01

197

Nuclear magnetic resonance, vibrational spectroscopic studies, physico-chemical properties and computational calculations on (nitrophenyl) octahydroquinolindiones by DFT method.  

PubMed

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

Pasha, M A; Siddekha, Aisha; Mishra, Soni; Azzam, Sadeq Hamood Saleh; Umapathy, S

2015-02-01

198

Communication: MULTIMODE calculations of low-lying vibrational states of NO3 using an adiabatic potential energy surface  

NASA Astrophysics Data System (ADS)

A semi-global, permutationally invariant potential energy surface for NO3 is constructed from a subset of roughly 5000 Multi-State CASPT2 calculations (MS-CAS(17e,13o)PT2/aug-cc-pVTZ) reported by Morokuma and co-workers [H. Xiao, S. Maeda, and K. Morokuma, J. Chem. Theory Comput. 8, 2600 (2012)]. The PES, with empirical adjustments to modify the energies of two fundamentals and a hot-band transition, is used in full-dimensional vibrational self-consistent field/virtual state configuration interaction calculations using the code MULTIMODE. Vibrational energies and assignments are given for the fundamentals and low-lying combination states, including two that have been the focus of some controversy. Energies of a number of overtone and combinations are shown to be in good agreement with experiment and previous calculations using a model vibronic Hamiltonian [C. S. Simmons, T. Ichino, and J. F. Stanton, J. Phys. Chem. Lett. 3, 1946 (2012)]. Notably, the fundamental v3 is calculated to be at 1099 cm-1 in accord with the prediction from the vibronic analysis, although roughly 30 cm-1 higher. The state at 1493 cm-1 is assigned as v3 + v4, which is also in agreement with the vibronic analysis and some experiments. Vibrational energies for 15NO3 are also presented and these are also in good agreement with experiment.

Homayoon, Zahra; Bowman, Joel M.

2014-10-01

199

Communication: MULTIMODE calculations of low-lying vibrational states of NO3 using an adiabatic potential energy surface.  

PubMed

A semi-global, permutationally invariant potential energy surface for NO3 is constructed from a subset of roughly 5000 Multi-State CASPT2 calculations (MS-CAS(17e,13o)PT2/aug-cc-pVTZ) reported by Morokuma and co-workers [H. Xiao, S. Maeda, and K. Morokuma, J. Chem. Theory Comput. 8, 2600 (2012)]. The PES, with empirical adjustments to modify the energies of two fundamentals and a hot-band transition, is used in full-dimensional vibrational self-consistent field/virtual state configuration interaction calculations using the code MULTIMODE. Vibrational energies and assignments are given for the fundamentals and low-lying combination states, including two that have been the focus of some controversy. Energies of a number of overtone and combinations are shown to be in good agreement with experiment and previous calculations using a model vibronic Hamiltonian [C. S. Simmons, T. Ichino, and J. F. Stanton, J. Phys. Chem. Lett. 3, 1946 (2012)]. Notably, the fundamental v3 is calculated to be at 1099 cm(-1) in accord with the prediction from the vibronic analysis, although roughly 30 cm(-1) higher. The state at 1493 cm(-1) is assigned as v3 + v4, which is also in agreement with the vibronic analysis and some experiments. Vibrational energies for (15)NO3 are also presented and these are also in good agreement with experiment. PMID:25362265

Homayoon, Zahra; Bowman, Joel M

2014-10-28

200

M-shaped asymmetric nonlinear oscillator for broadband vibration energy harvesting: Harmonic balance analysis and experimental validation  

NASA Astrophysics Data System (ADS)

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.

Leadenham, S.; Erturk, A.

2014-11-01

201

The Calculation of Accurate Harmonic Frequencies of Large Molecules: The Polycyclic Aromatic Hydrocarbons, a Case Study  

NASA Technical Reports Server (NTRS)

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.

Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Arnold, James O. (Technical Monitor)

1996-01-01

202

Vibrational Spectra, Theoretical Calculations, and Two-Dimensional Potential Energy Surface for the Ring-Puckering Vibrations of 2,4,7-Trioxa[3.3.0]octane.  

PubMed

2,4,7-Trioxa[3.3.0]octane (247TOO) is an unusual bicyclic molecule which can exist in four different conformational forms which are determined by the directions of the two ring- puckering motions. The vibrational assignments of 247TOO have been made based on its infrared and Raman spectra and theoretical density functional theory (DFT) calculations. The two ring-puckering motions (in-phase and out-of-phase) were observed in the Raman spectra of the liquid at 249 and 205 cm(-1) and these values correspond well to the DFT values of 247 and 198 cm(-1). Ab initio calculations were utilized to calculate the structures and conformational energies for the four energy minima and the barriers to interconversion and the data was utilized to generate a two-dimensional potential energy surface (PES) for the two ring-puckering motions. The resulting quantum state energies for this PES were then calculated in order to better understand the patterns that are produced when the PES has four energy minima at different energy values. The wave functions corresponding to the different quantum states were also calculated. The NMR spectrum of 247TOO showed the presence of the two lowest energy conformations, consistent with the results of the ab initio calculations. PMID:25514365

Chun, Hye Jin; Meinander, Niklas; Villarreal, John R; Laane, Jaan

2015-01-15

203

Collisional transfer of roto-vibrational energy from quantum calculations: The He-HF system  

Microsoft Academic Search

Summary  The problem of simultaneous vibrational and rotational excitations of HF molecules in collision with helium has been approached\\u000a via a quantum-mechanical treatment of the full dynamics and by employing a very accurate potential-energy surface suggested\\u000a earlier in the literature. The complicated coupling of rotational and vibrational channels has been partly simplified by taking\\u000a advantage of their different time scales, thus

F. A. Gianturco; U. T. Lamanna; G. Petrella

1984-01-01

204

Calculation of the vibrational spectra of RDX as a function of pressure using the Grimme DFT potential  

NASA Astrophysics Data System (ADS)

The density-functional theory (DFT) potential by Grimme has been proposed for describing long-range dispersion corrections. This potential has been implemented into the CRYSTAL09 program and used to calculate the vibrational spectra in RDX at equilibrium and as a function of pressure. The intensities, Born charge tensor, and high-frequency dielectric constant are reported and compared with prior theory and experiment where possible.

Perger, Warren; Flurchick, K. M.; Slough, Wil; Valenzano, Loredana

2011-06-01

205

A complete assignment of the vibrational spectra of sucrose in aqueous medium based on the SQM methodology and SCRF calculations.  

PubMed

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

Brizuela, Alicia Beatriz; Castillo, María Victoria; Raschi, Ana Beatriz; Davies, Lilian; Romano, Elida; Brandán, Silvia Antonia

2014-03-31

206

Structure and vibrational spectra of melaminium bis(trifluoroacetate) trihydrate: FT-IR, FT-Raman and quantum chemical calculations.  

PubMed

Melaminium bis(trifluoroacetate) trihydrate (MTFA), an organic material has been synthesized and single crystals of MTFA have been grown by the slow solvent evaporation method at room temperature. X-ray powder diffraction analysis confirms that MTFA crystal belongs to the monoclinic system with space group P2/c. The molecular geometry, vibrational frequencies and intensity of the vibrational bands have been interpreted with the aid of structure optimization based on density functional theory (DFT) B3LYP method with 6-311G(d,p) and 6-311++G(d,p) basis sets. The X-ray diffraction data have been compared with the data of optimized molecular structure. The theoretical results show that the crystal structure can be reproduced by optimized geometry and the vibrational frequencies show good agreement with the experimental values. The nuclear magnetic resonance (NMR) chemical shift of the molecule has been calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. HOMO-LUMO, and other related molecular and electronic properties are calculated. The Mulliken and NBO charges have also been calculated and interpreted. PMID:24556134

Sangeetha, V; Govindarajan, M; Kanagathara, N; Marchewka, M K; Gunasekaran, S; Anbalagan, G

2014-05-01

207

Studies on vibrational, NMR spectra and quantum chemical calculations of N-Succinopyridine: An organic nonlinear optical material  

NASA Astrophysics Data System (ADS)

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.

Kannan, V.; Thirupugalmani, K.; Brahadeeswaran, S.

2013-10-01

208

Molecular structure, vibrational spectral assignments, HOMO-LUMO, MESP, Mulliken analysis and thermodynamic properties of 2,6-xylenol and 2,5-dimethyl cyclohexanol based on DFT calculation  

NASA Astrophysics Data System (ADS)

The FT-IR and FT-Raman spectra of 2,6-xylenol and 2,5-dimethyl cyclohexanol are recorded in the region 4000-400 cm-1 and 3500-50 cm-1 respectively. The spectral data obtained are assigned to different normal modes by using of comparison with the theoretical values obtained by applying density functional theory (DFT/B3LYP) method with 6-31+G and 6-31++G basis set. The total energy distribution contributions of vibrations modes are distinguished through scaling factors. The calculated HOMO and LUMO energies shows that the charge transfers occur within the molecules. The harmonic frequencies obtained from these two methods are compared. The Mulliken, molecular electrostatic potentials analysis are calculated theoretically.

Arivazhagan, M.; Senthil kumar, J.

2015-02-01

209

Vibrational spectroscopic investigation (FT-IR and FT-Raman) using ab initio (HF) and DFT (B3LYP) calculations of 3-ethoxymethyl-1,4-dihydroquinolin-4-one  

NASA Astrophysics Data System (ADS)

The FT-IR and FT-Raman spectra of 3-ethoxymethyl-1,4-dihydroquinolin-4-one were recorded in the solid phase. The molecular geometry, harmonic vibrational frequencies, infrared intensities, Raman scattering activities, depolarization ratios and reduced masses were calculated by using the Hartree-Fock (HF) and density function theory (DFT/B3LYP) methods with the 6-311++G (d, p) basis set. The calculation results were applied to simulate infrared and Raman spectra of the title compound which showed good agreement with the observed spectra. A detailed interpretation of the infrared and Raman spectra of 3-ethoxymethyl-1,4-dihydroquinolin-4-one is reported. The theoretical spectrograms for FT-IR and FT-Raman spectra of the title compound have been constructed.

Al-Otaibi, Jamelah S.; Al-Wabli, Reem I.

2015-02-01

210

Vibrational spectroscopic investigation (FT-IR and FT-Raman) using ab initio (HF) and DFT (B3LYP) calculations of 3-ethoxymethyl-1,4-dihydroquinolin-4-one.  

PubMed

The FT-IR and FT-Raman spectra of 3-ethoxymethyl-1,4-dihydroquinolin-4-one were recorded in the solid phase. The molecular geometry, harmonic vibrational frequencies, infrared intensities, Raman scattering activities, depolarization ratios and reduced masses were calculated by using the Hartree-Fock (HF) and density function theory (DFT/B3LYP) methods with the 6-311++G (d,p) basis set. The calculation results were applied to simulate infrared and Raman spectra of the title compound which showed good agreement with the observed spectra. A detailed interpretation of the infrared and Raman spectra of 3-ethoxymethyl-1,4-dihydroquinolin-4-one is reported. The theoretical spectrograms for FT-IR and FT-Raman spectra of the title compound have been constructed. PMID:25180666

Al-Otaibi, Jamelah S; Al-Wabli, Reem I

2015-02-25

211

Molecular structure, vibrational spectral assignments, HOMO-LUMO, MESP, Mulliken analysis and thermodynamic properties of 2,6-xylenol and 2,5-dimethyl cyclohexanol based on DFT calculation.  

PubMed

The FT-IR and FT-Raman spectra of 2,6-xylenol and 2,5-dimethyl cyclohexanol are recorded in the region 4000-400cm(-1) and 3500-50cm(-1) respectively. The spectral data obtained are assigned to different normal modes by using of comparison with the theoretical values obtained by applying density functional theory (DFT/B3LYP) method with 6-31+G and 6-31++G basis set. The total energy distribution contributions of vibrations modes are distinguished through scaling factors. The calculated HOMO and LUMO energies shows that the charge transfers occur within the molecules. The harmonic frequencies obtained from these two methods are compared. The Mulliken, molecular electrostatic potentials analysis are calculated theoretically. PMID:25240827

Arivazhagan, M; Senthil Kumar, J

2015-02-25

212

Structural, vibrational, and quasiparticle band structure of 1,1-diamino-2,2-dinitroethelene from ab initio calculations  

SciTech Connect

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., E-mail: gvaithee@gmail.com [Advanced Centre of Research in High Energy Materials (ACRHEM), University of Hyderabad, Prof. C. R. Rao Road, Gachibowli, Hyderabad 500 046, Andhra Pradesh (India); Lebègue, S. [Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2, UMR CNRS 7036), Institut Jean Barriol, Université de Lorraine, BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-lès-Nancy (France)] [Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2, UMR CNRS 7036), Institut Jean Barriol, Université de Lorraine, BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-lès-Nancy (France)

2014-01-07

213

Structural, vibrational, and quasiparticle band structure of 1,1-diamino-2,2-dinitroethelene from ab initio calculations  

NASA Astrophysics Data System (ADS)

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

214

Terahertz spectroscopy and solid-state density functional theory calculation of anthracene: Effect of dispersion force on the vibrational modes  

SciTech Connect

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 *}.

Zhang, Feng; Tominaga, Keisuke, E-mail: atmyh@ntu.edu.tw, E-mail: tominaga@kobe-u.ca.jp, E-mail: junichi.nishizawa@hanken.jp [Molecular Photoscience Research Center, Kobe University, Nada, Kobe 657-0013 (Japan)] [Molecular Photoscience Research Center, Kobe University, Nada, Kobe 657-0013 (Japan); Hayashi, Michitoshi, E-mail: atmyh@ntu.edu.tw, E-mail: tominaga@kobe-u.ca.jp, E-mail: junichi.nishizawa@hanken.jp; Wang, Houng-Wei [Center for Condensed Matter Sciences, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei 10617, Taiwan (China)] [Center for Condensed Matter Sciences, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei 10617, Taiwan (China); Kambara, Ohki; Sasaki, Tetsuo [Research Institute of Electronics, Shizuoka University, 3-5-1 Jyohoku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan)] [Research Institute of Electronics, Shizuoka University, 3-5-1 Jyohoku, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Nishizawa, Jun-ichi, E-mail: atmyh@ntu.edu.tw, E-mail: tominaga@kobe-u.ca.jp, E-mail: junichi.nishizawa@hanken.jp [Jun-ichi Nishizawa Memorial Research Center, Tohoku University, 519-1176 Aoba, Aramaki, Aoba-ku, Sendai 980-0845 (Japan)] [Jun-ichi Nishizawa Memorial Research Center, Tohoku University, 519-1176 Aoba, Aramaki, Aoba-ku, Sendai 980-0845 (Japan)

2014-05-07

215

A new treatment for predicting the self-excited vibrations of nonlinear systems with frictional interfaces: The Constrained Harmonic Balance Method, with application to disc brake squeal  

NASA Astrophysics Data System (ADS)

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.

Coudeyras, N.; Sinou, J.-J.; Nacivet, S.

2009-01-01

216

A unifying model for non-adiabatic coupling at metallic surfaces beyond the local harmonic approximation: from vibrational relaxation to scanning tunneling microscopy.  

PubMed

A model for treating excitation and relaxation of adsorbates at metallic surfaces induced by non-adiabatic coupling is developed. The derivation is based on the concept of resonant electron transfer, where the adsorbate serves as a molecular bridge for the inelastic transition between an electron source and a sink. In this picture, energy relaxation and scanning tunneling microscopy (STM) at metallic surfaces are treated on an equal footing as a quasi-thermal process. The model goes beyond the local harmonic approximation and allows for an unbiased description of floppy systems with multiple potential wells. Further, the limitation of the product ansatz for the vibronic wave function to include the position-dependence of the non-adiabatic couplings is avoided by explicitly enforcing detailed balance. The theory is applied to the excitation of hydrogen on palladium, which has multiple local potential minima connected by low energy barriers. The main aspects investigated are the lifetimes of adsorbate vibrations in different adsorption sites, as well as the dependence of the excitation, response, and transfer rates on an applied potential bias. The excitation and relaxation simulations reveal intricate population dynamics that depart significantly from the simplistic tunneling model in a truncated harmonic potential. In particular, the population decay from an initially occupied local minimum induced by the contact with an STM tip is found to be better described by a double exponential. The two rates are interpreted as a response to the system perturbation and a transfer rate following the perturbation. The transfer rate is found to obey a power law, as was the case in previous experimental and theoretical work. PMID:23822226

Tremblay, Jean Christophe

2013-06-28

217

A unifying model for non-adiabatic coupling at metallic surfaces beyond the local harmonic approximation: From vibrational relaxation to scanning tunneling microscopy  

NASA Astrophysics Data System (ADS)

A model for treating excitation and relaxation of adsorbates at metallic surfaces induced by non-adiabatic coupling is developed. The derivation is based on the concept of resonant electron transfer, where the adsorbate serves as a molecular bridge for the inelastic transition between an electron source and a sink. In this picture, energy relaxation and scanning tunneling microscopy (STM) at metallic surfaces are treated on an equal footing as a quasi-thermal process. The model goes beyond the local harmonic approximation and allows for an unbiased description of floppy systems with multiple potential wells. Further, the limitation of the product ansatz for the vibronic wave function to include the position-dependence of the non-adiabatic couplings is avoided by explicitly enforcing detailed balance. The theory is applied to the excitation of hydrogen on palladium, which has multiple local potential minima connected by low energy barriers. The main aspects investigated are the lifetimes of adsorbate vibrations in different adsorption sites, as well as the dependence of the excitation, response, and transfer rates on an applied potential bias. The excitation and relaxation simulations reveal intricate population dynamics that depart significantly from the simplistic tunneling model in a truncated harmonic potential. In particular, the population decay from an initially occupied local minimum induced by the contact with an STM tip is found to be better described by a double exponential. The two rates are interpreted as a response to the system perturbation and a transfer rate following the perturbation. The transfer rate is found to obey a power law, as was the case in previous experimental and theoretical work.

Tremblay, Jean Christophe

2013-06-01

218

Temperature-dependent vibrational spectroscopic study and DFT calculations of the sorbic acid.  

PubMed

This work reports a temperature-dependent vibrational spectroscopic study of the sorbic acid (C6H8O2), as well as the mode assignment at ambient conditions, based on the density functional theory. Temperature-dependent vibrational properties have been performed in polycrystalline sorbic acid through both Raman and infrared spectroscopy in the 20-300 K and 80-300 K temperature ranges, respectively. These studies present the occurrence of some modifications in the Raman spectra that could be interpreted as a low temperature phase transition undergone by sorbic acid from the monoclinic phase to an unknown phase with conformational change of the molecules in the unit cell. PMID:25310262

Saraiva, G D; Nogueira, C E S; Freire, P T C; de Sousa, F F; da Silva, J H; Teixeira, A M R; Mendes Filho, J

2015-02-25

219

Improved methods for Feynman path integral calculations and their application to calculate converged vibrational-rotational partition functions, free energies, enthalpies, entropies, and heat capacities for methane  

NASA Astrophysics Data System (ADS)

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.

2015-01-01

220

Calculation of the vibrational partition function of diatomic molecules from a scaled Wigner-Kirkwood expansion  

NASA Astrophysics Data System (ADS)

New approximations to the partition function of diatomic molecules are given. The semiclassical Wigner-Kirkwood expansion truncated at the second or fourth order diverges as Ticons/Journals/Common/to" ALT="to" ALIGN="TOP"/>icons/Journals/Common/infty" ALT="infty" ALIGN="TOP"/>. Various methods of scaling the Wigner-Kirkwood expansion are given which avoid this disadvantage and give sufficient accuracy in the low-temperature region. In addition, two modifications of the Pitzer-Gwinn method are discussed. Most molecular potentials can be considered almost harmonic near the minimum. For the scaling of the Wigner-Kirkwood expansion, therefore, a functional form is chosen, which would be exact for every temperature in the case of a purely harmonic potential. In the high-temperature limit the scaled and the conventional Wigner-Kirkwood expansion become identical.

Taubmann, G.; Witschel, W.; Schoendorff, L.

1999-06-01

221

DVR3D: a program suite for the calculation of rotation-vibration spectra of triatomic molecules  

NASA Astrophysics Data System (ADS)

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 b

Tennyson, Jonathan; Kostin, Maxim A.; Barletta, Paolo; Harris, Gregory J.; Polyansky, Oleg L.; Ramanlal, Jayesh; Zobov, Nikolai F.

2004-11-01

222

Robust optimization of an automobile rearview mirror for vibration reduction  

Microsoft Academic Search

.   An automobile outside rearview mirror system has been analysed and designed to reduce vibration with a finite element model.\\u000a Modal analysis is conducted for the calculation of natural frequencies. Harmonic analysis is utilized to estimate the displacements\\u000a of the glass surface under dynamic loads. The model is verified with the vibration experiment for the parts and the assembled\\u000a body.

K.-H. Hwang; K.-W. Lee; G.-J. Park

2001-01-01

223

A receptance harmonic balance technique for the computation of the vibration of a whole aero-engine model with nonlinear bearings  

NASA Astrophysics Data System (ADS)

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.

Bonello, Philip; Minh Hai, Pham

2009-07-01

224

Characterization of a genuin iron(V) - nitrido species by nuclear resonant vibrational spectroscopy coupled to density functional calculations.  

SciTech Connect

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]{sup +} 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 d{sup 3} 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{sup -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{sup -1}. Anharmonic contributions to the Fe-N stretching frequency have been evaluated and have been found to be small (-5.5 cm{sup -1}). The NRVS data provided a unique opportunity to obtain this vibrational information, which had eluded characterization by more traditional vibrational spectroscopies.

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.; X-Ray Science Division; Institut of Physikalische und Theoretische Chemie; SSRL; Standford Univ.; Max-Planck Institut fur Bioanogranische Chemie; Univ. of California at Davis; LBNL

2007-01-01

225

Characterization of a Genuine Lron(V)-Nitrido Species By Nuclear Resonant Vibrational Spectroscopy Coupled to Density Functional Calculations  

SciTech Connect

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.

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

226

Vibrational dynamics of the H5+ and its isotopologues from multiconfiguration time-dependent Hartree calculations  

NASA Astrophysics Data System (ADS)

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.

Valdés, Álvaro; Prosmiti, Rita; Delgado-Barrio, Gerardo

2012-12-01

227

Multi-layer Lanczos iteration approach to calculations of vibrational energies and dipole transition intensities for polyatomic molecules  

NASA Astrophysics Data System (ADS)

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.

Yu, Hua-Gen

2015-01-01

228

Crystal structure, vibrational studies, optical properties and DFT calculations of 2-amino-5-diethyl-aminopentanium tetrachlorocadmate (II)  

NASA Astrophysics Data System (ADS)

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 Nsbnd 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.

Baklouti, Yosra; chaari, Najla; Feki, Habib; Chniba-Boudjada, Nassira; Zouari, Fatma

2015-02-01

229

Crystal structure, vibrational studies, optical properties and DFT calculations of 2-amino-5-diethyl-aminopentanium tetrachlorocadmate (II).  

PubMed

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

Baklouti, Yosra; chaari, Najla; Feki, Habib; Chniba-Boudjada, Nassira; Zouari, Fatma

2015-02-01

230

Quasiclassical trajectory calculations analyzing the role of vibrational and translational energy in the F+CH2D2 reaction  

NASA Astrophysics Data System (ADS)

An exhaustive state-to-state dynamics study was performed to analyze the effects of vibrational excitation and translational energy on the dynamics of the F+CH2D2 gas-phase reaction, which are connected to such issues as bond selectivity, mode selectivity, and Polanyi's rules. This reaction can evolve along two channels: D-abstraction, DF(v')+CH2D(v'), and H-abstraction, HF(v')+CHD2(v'). Quasiclassical trajectory calculations were performed on an analytical potential energy surface previously developed by our group. Vibrational excitation of the C-D or C-H mode of CH2D2 favors slightly the D-abstraction over the H-abstraction, indicating that this reaction does not exhibit bond selectivity and suggesting a breakdown of the spectator model. For D-abstraction, the vibrational excitation of the nonreactive C-H stretch mode is partially retained in the products, and for H-abstraction, the excitation of the nonreactive C-D stretch mode is also partially retained in the products, indicating that this reaction exhibits mode selectivity only partially. Moreover, the independent excitation of the C-H symmetric or asymmetric stretch modes leads to reactions with similar (practically identical) reaction cross sections and product scattering distributions, discarding bond selectivity and mode selectivity for this reaction. Finally, for this "early transition state" reaction, vibrational energy is more effective in driving the reaction than an equivalent amount of energy in translation, indicating that the application of the Polanyi rules that are well established in atom-diatom reactions is neither straightforward nor always valid in polyatomic reactions. All these results were interpreted on the basis of strong coupling between modes along the reaction path, a behavior which seems to be more of the general tendency than the exception in polyatomic reactions.

Espinosa-García, Joaquín

2009-02-01

231

The vibrational and NMR spectra, conformations and ab initio calculations of 1-aminoethylidene propanedinitrile and its N-methyl derivatives  

NASA Astrophysics Data System (ADS)

The IR and Raman spectra of 1-aminoethylidene propanedinitrile (AE) [H 2N-C(CH 3)?C(CN) 2], 1-(methylamino)ethylidene propanedinitrile (MAE) [CH 3NH-C(CH 3)?C(CN) 2] and 1-(dimethylamino)ethylidene propanedinitrile (DMAE) [(CH 3) 2N-C(CH 3)?C(CN) 2] were recorded as solids and solutes in various solvents in the region 4000-50 cm -1. AE and DMAE can exist only as single conformers. From the vibrational and NMR spectra of MAE in solutions, the existence of two conformers with the methyl group oriented anti and syn towards the double C?C bond were confirmed. The enthalpy difference ? H0 between the conformers was measured to be 1.9±1.3 kJ mol -1 from the NMR spectra in DMSO solution. Semi-empirical (AM1, PM3, MNDO, MINDO3) and ab initio SCF calculations using a DZP basis set were carried out for all the three compounds. The calculations support the existence of two conformers anti and syn for MAE with anti being 9.4 kJ mol -1 more stable than syn from ab initio and 7.4, 12.0, 7.8 and 9.2 kJ mol -1 from AM1, PM3, MNDO and MINDO3 calculations, respectively. Finally, complete assignments of the vibrational spectra for all the three compounds were made with the aid of normal coordinate calculations employing scaled ab initio force constants. The scale factors from the similar aminomethylene propanedinitrile and its N-methyl derivatives were used and a very good agreement between calculated and experimental frequencies was achieved.

Gatial, A.; Sklenák, Š.; Milata, V.; Biskupi?, S.; Salzer, R.; Scheller, D.; Woelki, G.

1999-10-01

232

Force-field calculation and geometry of the HOOO radical.  

PubMed

High-level ab initio calculations using the Davidson-corrected multireference configuration interaction (MRCI) level of theory with Dunning's correlation consistent basis sets and force-field calculations were performed for the HOOO radical. The harmonic vibrational frequencies and their anharmonic constants obtained by the force-field calculations reproduce the IR-UV experimental vibrational frequencies with errors less than 19 cm(-1). The rotational constants for the ground vibrational state obtained using the vibration-rotation interaction constants of the force-field calculations also reproduce the experimentally determined rotational constants with errors less than 0.9%, indicating that the present quantum chemical calculations and the derived spectroscopic constants have high accuracy. The equilibrium structure was determined from the experimentally determined rotational constants combined with the theoretically derived vibration-rotation interaction constants. The determined geometrical parameters agree well with the results of the present MRCI calculation. PMID:24028111

Suma, Kohsuke; Sumiyoshi, Yoshihiro; Endo, Yasuki

2013-09-01

233

Force-field calculation and geometry of the HOOO radical  

NASA Astrophysics Data System (ADS)

High-level ab initio calculations using the Davidson-corrected multireference configuration interaction (MRCI) level of theory with Dunning's correlation consistent basis sets and force-field calculations were performed for the HOOO radical. The harmonic vibrational frequencies and their anharmonic constants obtained by the force-field calculations reproduce the IR-UV experimental vibrational frequencies with errors less than 19 cm-1. The rotational constants for the ground vibrational state obtained using the vibration-rotation interaction constants of the force-field calculations also reproduce the experimentally determined rotational constants with errors less than 0.9%, indicating that the present quantum chemical calculations and the derived spectroscopic constants have high accuracy. The equilibrium structure was determined from the experimentally determined rotational constants combined with the theoretically derived vibration-rotation interaction constants. The determined geometrical parameters agree well with the results of the present MRCI calculation.

Suma, Kohsuke; Sumiyoshi, Yoshihiro; Endo, Yasuki

2013-09-01

234

Comparison of DFT with Traditional Methods for the Calculation of Vibrational Frequencies and Bond Energies  

NASA Technical Reports Server (NTRS)

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.

Bauschlicher, Charles W.; Arnold, James O. (Technical Monitor)

1997-01-01

235

Rotation-vibration energy levels of H 2O and C 3 calculated using the nonrigid bender Hamiltonian  

NASA Astrophysics Data System (ADS)

We have written a new computer program for diagonalizing the nonrigid bender Hamiltonian, and have based the program entirely on the theory as reviewed by P. Jensen [ Comp. Phys. Rep.1, 1-56 (1983)] and P. Jensen and P. R. Bunker [ J. Mol. Spectrosc.118, 18-39 (1986)]. Using this program we can calculate the rotation-vibration energy levels of a triatomic molecule from the potential energy function. The program is an improvement over an earlier version, particularly in the systematic treatment of all singular terms, and in the allowance made for the dependence of all perturbation energy denominators on the bending quantum number v2 and rotation quantum number K. The new program can be used for symmetric and unsymmetric triatomic molecules. In the present paper we test the program by applying it to the calculation of the rotation-vibration energy levels of C 3 from an ab initio potential surface, and of H 2O from ab initio and experimental potential surfaces.

Beardsworth, R.; Bunker, P. R.; Jensen, Per; Kraemer, W. P.

1986-07-01

236

Molecular structure, vibrational and EPR spectra of Cu(II) chloride complex of 4-amino-1-methylbenzene combined with quantum chemical calculations  

NASA Astrophysics Data System (ADS)

Transition metal complex of CuCl2 with L = 4-amino-1-methylbenzene, i.e., [CuCl2L2], has been synthesized and characterized by elemental analyses, FT-IR, dispersive Raman and EPR methods. The geometrical structure and vibrational spectra of L and [CuCl2L2] have been investigated in terms of density functional calculations employing the 6-311G+(d,p) basis set. The normal modes have been assigned on the basis of the percent potential energy distribution (PED) of the internal motions in each vibrational modes. The effects of the coordination on vibrational modes have been investigated. The experimental vibrational and EPR spectral studies and theoretical calculations find the title complex as a doublet with one unpaired electron.

Bardakç?, T.; Kumru, M.; Güner, S.

2013-12-01

237

Molecular structure and vibrational analysis of Trifluoperazine by FT-IR, FT-Raman and UV-Vis spectroscopies combined with DFT calculations  

NASA Astrophysics Data System (ADS)

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.

Rajesh, P.; Gunasekaran, S.; Gnanasambandan, T.; Seshadri, S.

2015-02-01

238

Molecular structure and vibrational analysis of Trifluoperazine by FT-IR, FT-Raman and UV-Vis spectroscopies combined with DFT calculations.  

PubMed

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. PMID:25305610

Rajesh, P; Gunasekaran, S; Gnanasambandan, T; Seshadri, S

2015-02-25

239

Variational Calculations of Ro-Vibrational Energy Levels and Transition Intensities for Tetratomic Molecules  

NASA Technical Reports Server (NTRS)

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.

Schwenke, David W.; Langhoff, Stephen R. (Technical Monitor)

1995-01-01

240

Efficient quantum calculations of vibrational states of vinylidene in full dimensionality: A scheme with combination of methods  

NASA Astrophysics Data System (ADS)

Full-dimensional quantum calculations of vibrational states of C2H2 and C2D2 are performed in the high-energy region (above 20400cm-1 relative to the acetylene minimum). The theoretical scheme is a combination of several methods. To exploit the full parity and permutation symmetry, the CC-HH diatom-diatom Jacobi coordinates are chosen; phase space optimization in combination with physical considerations is used to obtain an efficient radial discrete variable representation, whereas a basis contraction scheme is applied for angular coordinates. The preconditioned inexact spectral transform method combined with an efficient preconditioner is employed to compute eigenstates within a desired spectral window. The computation is efficient. More definite assignments on vinylidene states than previous studies are acquired using the normal mode projection; in particular, a consistent analysis of the ?1 (symmetric CH stretch) state is provided. The computed vinylidene vibrational energy levels are in general good agreement with experiment, and several vinylidene states are reported for the first time.

Li, Bin; Bian, Wensheng

2008-07-01

241

Calculating the effect of vacancies on the thermodynamic functions and frequencies of normal vibrations of a Lennard-Jones monoatomic crystal  

NASA Astrophysics Data System (ADS)

Four main functions of a Lennard-Jones defect argon crystal with an FCC lattice are considered in the context of the lattice gas model: Helmholtz free energy, entropy, internal energy, and heat capacity at a constant volume (allowing for normal vibrations of a solid). Properties of the defect crystal are calculated from the distribution function of the frequencies of an ideal crystal, and corrections to it that reflect local atomic vibrations around vacancies, in the context of the Lifshits linear approximation according to vacancy density. To find the free energy of a defect-free ideal crystal, frequencies of normal vibrations of the crystal are calculated with allowance for the interactions of the four nearest neighbors. The nonlocality of the chemical potentials of the atoms of a solid is discussed, and the influence of contributions from various segments of the vibrational spectrum to the values of thermodynamic functions is investigated. It is shown that ignoring the acoustic or antiphase segments of the spectrum when calculating the free energy leads to increasing of its deviation from the one calculated using the full vibrational spectrum with an increase in temperature. It is concluded that the nonequilibrium state of the defect crystal can lead to negative values of heat capacity at a constant volume.

Titov, S. V.; Tovbin, Yu. K.

2014-12-01

242

Ab Initio Calculation of Accurate Vibrational Frequencies for Molecules of Interest in Atmospheric Chemistry  

NASA Technical Reports Server (NTRS)

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.

Lee, Timothy J.; Langhoff, Stephen R. (Technical Monitor)

1996-01-01

243

A unified theory of uncontrolled rectifiers, discharge lamps and arc furnaces. I. An analytical approach for normalized harmonic emission calculations  

Microsoft Academic Search

Under certain assumptions, similar models can be applied for rectifiers and devices with electric arc characteristic. The analysis considers single and three-phase uncontrolled rectifiers with continuous and discontinuous evolution of the AC current. It leads to four possible situations which fit with the harmonic behaviour of discharge lamps, arc furnaces and rectifiers with capacitive DC smoothing. A very useful set

J. G. Mayordomo; A. Hernandez; R. Asensi; L. F. Beites; M. Izzeddine

1998-01-01

244

Experimental study on the structure and vibrational, thermal and dielectric properties of bis(2-methylanilinium) selenate accomplished with DFT calculation  

NASA Astrophysics Data System (ADS)

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.

Ben hassen, C.; Boujelbene, M.; Bahri, M.; Zouari, N.; Mhiri, T.

2014-09-01

245

Calculation of Dynamic Loads Due to Random Vibration Environments in Rocket Engine Systems  

NASA Technical Reports Server (NTRS)

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.

Christensen, Eric R.; Brown, Andrew M.; Frady, Greg P.

2007-01-01

246

Theoretical calculations and vibrational potential energy surface of 4-silaspiro(3,3)heptane  

SciTech Connect

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.

Ocola, Esther J.; Medders, Cross; Laane, Jaan, E-mail: laane@mail.chem.tamu.edu [Department of Chemistry, Texas A and M University, College Station, Texas 77843-3255 (United States)] [Department of Chemistry, Texas A and M University, College Station, Texas 77843-3255 (United States); Meinander, Niklas [Department of Military Technology, Finnish National Defence University, P.O. Box 7, 00861 Helsinki (Finland)] [Department of Military Technology, Finnish National Defence University, P.O. Box 7, 00861 Helsinki (Finland)

2014-04-28

247

Analytic Continuation of Harmonic Sums  

E-print Network

We present a method for calculating any (nested) harmonic sum to arbitrary accuracy for all complex values of the argument. The method utilizes the relation between harmonic sums and (derivatives of) Hurwitz zeta functions, which allows a harmonic sum to be calculated as an expansion valid for large values of its argument. A program for implementing this method is also provided.

S. Albino

2009-03-06

248

Storage capacity and vibration frequencies of guest molecules in CH4 and CO2 hydrates by first-principles calculations.  

PubMed

Using first-principle calculations at B97-D/6-311++G(2d,2p) level, we systematically explore the gas capacity of five standard water cavities (5(12), 4(3)5(6)6(3), 5(12)6(2), 5(12)6(4), and 5(12)6(8)) in clathrate hydrate and study the inclusion complexes to infer general trends in vibrational frequencies of guest molecules as a function of cage size and number of guest molecules. In addition, the Raman spectra of hydrates from CO2/CH4 gases are simulated. From our calculations, the maximum cage occupancy of the five considered cages (5(12), 4(3)5(6)6(3), 5(12)6(2), 5(12)6(4), and 5(12)6(8)) is one, one, two, three, and seven for both CH4 and CO2 guest molecules, respectively. Meanwhile, the optimum cage occupancy are one, one, one, two, and four for CO2 molecules and one, one, two, three, and five for CH4 molecules, respectively. Both the C-H stretching frequency of CH4 and the C-O stretching frequency of CO2 gradually decrease as size of the water cages increases. Meanwhile, the C-H stretching frequency gradually increases as the amount of CH4 molecules in the water cavity (e.g., 5(12)6(8)) increases. PMID:24320601

Cao, Xiaoxiao; Su, Yan; Liu, Yuan; Zhao, Jijun; Liu, Changling

2014-01-01

249

Calculating vibrational spectra with sum of product basis functions without storing full-dimensional vectors or matrices  

NASA Astrophysics Data System (ADS)

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.

Leclerc, Arnaud; Carrington, Tucker

2014-05-01

250

Calculating vibrational spectra with sum of product basis functions without storing full-dimensional vectors or matrices.  

PubMed

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 10(20) components and would hence require about 8 × 10(11) 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. PMID:24811629

Leclerc, Arnaud; Carrington, Tucker

2014-05-01

251

MORSMATEL: a rapid and efficient code to calculate vibration-rotational matrix elements for r-dependent operators of two Morse oscillators  

NASA Astrophysics Data System (ADS)

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.

Lopez-Piñeiro, A.; Sanchez, M. L.; Moreno, B.

1992-06-01

252

Molecular conformational analysis, vibrational spectra and normal coordinate analysis of trans-1,2-bis(3,5-dimethoxy phenyl)-ethene based on density functional theory calculations  

NASA Astrophysics Data System (ADS)

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).

Joseph, Lynnette; Sajan, D.; Chaitanya, K.; Isac, Jayakumary

2014-03-01

253

Analysis of ?-PHASE Rdx Vibrational Lattice Modes Under Hydrostatic Pressur  

NASA Astrophysics Data System (ADS)

Calculations using the all-electron CRYSTAL06 program employing density functional theory are used to calculate the terahertz vibrational frequencies of ?-phase RDX. The lowest frequency infrared active lattice modes are investigated as a function of hydrostatic pressure from ambient conditions up to 3 GPa. A given mode may be composed of both external and internal vibration contributions, with the composition changing as a function of pressure. The anharmonic deviation of each mode from simple harmonic behavior as a function of pressure is also explored.

Slough, W. J.; Perger, W. F.

2009-12-01

254

Intermolecular vibrations of (CH2)2O-HF and -DF hydrogen bonded complexes investigated by Fourier transform infrared spectroscopy and ab initio calculations.  

PubMed

A series of Fourier transform infrared spectra (FTIR) of the hydrogen bonded complexes (CH(2))(2)O-HF and -DF have been recorded in the 50-750 cm(-1) range up to 0.1 cm(-1) resolution in a static cell maintained at near room temperature. The direct observation of three intermolecular transitions enabled us to perform band contour analysis of congested cell spectra and to determine reliable rovibrational parameters such as intermolecular frequencies, rovibrational and anharmonic coupling constants involving two l(1) and l(2) librations and one ? stretching intermolecular motion. Inter-inter anharmonic couplings could be identified between ?(l(1)), ?(l(2)), ?(?) and the two lowest frequency bending modes. The positive sign of coupling constants (opposite with respect to acid stretching intra-inter ones) reveals a weakening of the hydrogen bond upon intermolecular excitation. The four rovibrational parameters ?(?) and x(?j) (j = ?, ?(1), ?(2)) derived in the present far-infrared study and also in a previous mid-infrared one [Phys. Chem. Chem. Phys. 2005, 1, 592] make deviations appear smaller than 1% for frequencies and 12% for coupling constants which gives confidence to the reliability of the data obtained. Anharmonic frequencies obtained at the MP2 level with Aug-cc-pvTZ basis set agree well with experimental values over a large set of frequencies and coupling constants. An estimated anharmonic corrected value of the dissociation energy D for both oxirane-HF (2424 cm(-1)) and -DF (2566 cm(-1)) has been derived using a level of theory as high as CCSD(T)/Aug-cc-pvQZ, refining the harmonic value previously calculated for oxirane-HF with the MP2 method and a smaller basis set. Finally, contrary to short predissociation lifetimes evidenced for acid stretching excited states, any homogeneous broadening related to vibrational dynamics of (CH(2))(2)O-HF and -DF has been observed within the three highest frequency intermolecular states, as expected with low excitation energies largely below the dissociation limit as well as a negligible IVR contribution. PMID:20717572

Cirtog, M; Asselin, P; Soulard, P; Madebène, B; Alikhani, M E

2010-10-14

255

Optimal geometries and harmonic vibrational frequencies of the global minima of water clusters (H2O)n, n=2-6, and several hexamer local minima at the CCSD(T) level of theory  

SciTech Connect

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 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) 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 Å. 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.

Miliordos, Evangelos; Apra, Edoardo; Xantheas, Sotiris S.

2013-09-21

256

Ion-orbital coupling in Car-Parrinello calculations of hydrogen-bond vibrational dynamics: case study with the NH3-HCl dimer.  

PubMed

We have performed Car-Parrinello molecular dynamics (CPMD) calculations of the hydrogen-bonded NH(3)-HCl dimer. Our main aim is to establish how ionic-orbital coupling in CPMD affects the vibrational dynamics in hydrogen-bonded systems by characterizing the dependence of the calculated vibrational frequencies upon the orbital mass in the adiabatic limit of Car-Parrinello calculations. We use the example of the NH(3)-HCl dimer because of interest in its vibrational spectrum, in particular the magnitude of the frequency shift of the H-Cl stretch due to the anharmonic interactions when the hydrogen bond is formed. We find that an orbital mass of about 100 a.u. or smaller is required in order for the ion-orbital coupling to be linear in orbital mass, and the results for which can be accurately extrapolated to the adiabatic limit of zero orbital mass. We argue that this is general for hydrogen-bonded systems, suggesting that typical orbital mass values used in CPMD are too high to accurately describe vibrational dynamics in hydrogen-bonded systems. Our results also show that the usual application of a scaling factor to the CPMD frequencies to correct for the effects of orbital mass is not valid. For the dynamics of the dimer, we find that the H-Cl stretch and the N-H-Cl bend are significantly coupled, suggesting that it is important to include the latter degree of freedom in quantum dynamical calculations. Results from our calculations with deuterium-substitution show that both these degrees of freedom have significant anharmonic interactions. Our calculated frequency for the H-Cl stretch using the Becke-exchange Lee-Yang-Parr correlation functional compares reasonably well with a previous second-order Møller-Plesset calculation with anharmonic corrections, although it is low compared to the experimental value for the dimer trapped in a neon-matrix. PMID:21932876

Ong, S W; Lee, B X B; Kang, H C

2011-09-14

257

First-principle calculation and assignment for vibrational spectra of Ba(Mg1/3Nb2/3)O3 microwave dielectric ceramic  

NASA Astrophysics Data System (ADS)

1:2 B-site cation ordered Ba(Mg1/3Nb2/3)O3 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 A1g(4) (789 cm-1) can be described as the breathing vibration of NbO6. The IR modes Eu(1) (149 cm-1) and A2u(2) (212 cm-1), which can be described as the twisting vibrations of Ba-MgO6/Ba-NbO6 on the a-b plane and the stretching vibrations of Ba-MgO6/Ba-NbO6 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.

Diao, Chuan-Ling; Wang, Chun-Hai; Luo, Neng-Neng; Qi, Ze-Ming; Shao, Tao; Wang, Yu-Yin; Lu, Jing; Wang, Quan-Chao; Kuang, Xiao-Jun; Fang, Liang; Shi, Feng; Jing, Xi-Ping

2014-03-01

258

Calculation of exact vibrational spectra for P{sub 2}O and CH{sub 2}NH using a phase space wavelet basis  

SciTech Connect

‘‘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.

Halverson, Thomas, E-mail: tom.halverson@ttu.edu; Poirier, Bill [Department of Chemistry and Biochemistry and Department of Physics, Texas Tech University, P.O. Box 41061, Lubbock, Texas 79409-1061 (United States)

2014-05-28

259

Ab initio calculation of Raman vibrational signatures of 2,4-dinitrotoluene, 2,6-dinitrotoluene and 2,4,6-trinitrotoluene  

NASA Astrophysics Data System (ADS)

The Raman vibrational frequencies in the finger print region (700-1600 cm -1) have been calculated for 2,4- dinitrotoluene, 2,6-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT). The Raman vibrational intensities and frequencies for these molecules have been calculated using B3LYP Density Functional Theory method with 6-311+G** and Sadlejs medium-sized polarized basis sets (Sadlej pVTZ). The normal mode assignments in the finger print region were carried out by Normal Coordinate Analysis, where localized and de-localized coordinates were used to facilitate an accurate description of the vibrational modes. The Raman intensities were calculated from the Raman scattering cross sections using the ab initio calculated Raman scattering activities. Comparison of these intensities using different basis sets indicates that the Sadlej pVTZ basis sets increase the calculated intensities for the NO II symmetric stretching and bending frequencies by more than 15 % relative to 6-311+G** basis. The potential energy distribution for the symmetric and asymmetric NO II stretches indicates that 2-NO II and 6-NO II couple strongly in 2,6-DNT and 2,4,6-TNT, while 2-NO II and 4-NO II groups couple weakly in 2,4- DNT. These findings suggest that the coupling strength of 2-NO II, 6-NO II and 4-NO II groups can be used to distinguish between dinitro and trinitro toluenes.

Castillo-Chará, Jairo; Manrique-Bastidas, César; Mina, Nairmen; Castro, Miguel E.; Hernández-Rivera, Samuel P.

2007-09-01

260

Experimental Harmonic Motion  

NASA Astrophysics Data System (ADS)

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.

Searle, G. F. C.

2014-05-01

261

A simple frequency-independent method for calculating the reactive and harmonic current in a nonlinear load  

Microsoft Academic Search

A basic criterion that determines the behavior of an active power filter is the method of calculating the reference current. There are many ways of generating this reference, but the methods are generally complex and hard to tune. This paper describes a simple and effective method for calculating the reference current necessary to feed a shunt active power filter to

J. Sebastian Tepper; Juan W. Dixon; Gustavo Venegas; L. Moran

1996-01-01

262

Hybrid MP2/MP4 potential surfaces in VSCF calculations of IR spectra: applications for organic molecules.  

PubMed

This study introduces an improved hybrid MP2/MP4 ab initio potential for vibrational spectroscopy calculations which is very accurate, yet without high computational demands. The method uses harmonic vibrational calculations with the MP4(SDQ) potential to construct an improved MP2 potential by coordinate scaling. This improved MP2 potential is used for the anharmonic VSCF calculation. The method was tested spectroscopically for four molecules: butane, acetone, ethylene and glycine. Very good agreement with experiment was found. For most of the systems, the more accurate harmonic treatment considerably improved the MP2 anharmonic results. PMID:23838574

Knaanie, Roie; Šebek, Ji?í; Kalinowski, Jaroslaw; Benny Gerber, R

2014-02-01

263

On harmonic binomial series  

E-print Network

We evaluate binomial series with harmonic number coefficients, providing recursion relations, integral representations, and several examples. The results are of interest to analytic number theory, the analysis of algorithms, and calculations of theoretical physics, as well as other applications.

Mark W. Coffey

2008-12-09

264

A formulation of rotor-airframe coupling for design analysis of vibrations of helicopter airframes  

NASA Technical Reports Server (NTRS)

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.

Kvaternik, R. G.; Walton, W. C., Jr.

1982-01-01

265

Molecular structure, vibrational spectra and HOMO, LUMO analysis of yohimbine hydrochloride by density functional theory and ab initio Hartree-Fock calculations.  

PubMed

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. PMID:21856216

Joshi, Bhawani Datt; Srivastava, Anubha; Tandon, Poonam; Jain, Sudha

2011-11-01

266

Intramolecular Dynamics Probed using High Harmonic Generation  

NASA Astrophysics Data System (ADS)

We observed intramolecular dynamics as a modulation in high harmonic emission. We excite coherent vibrations in CF3Cl using impulsive Raman scattering with a short laser pulse. A second laser pulse generates high harmonics. The harmonic yield is observed to oscillate at frequencies corresponding to three vibrational modes of CF3Cl. In a second experiment, we used UV light to excite and dissociate CF3I, and follow the dynamic evolution by monitoring the harmonic yield. We observe a large modulation of the harmonic yield, likely due to resonance excitation and subsequent dissociation of the molecule. We speculate that the less-than full baseline recovery after the UV pulse is due to ionization, and that the harmonic yield is sensitive to the bond length during dissociation. By these two experiments, we confirm that high harmonic generation is a sensitive probe of intramolecular dynamics and may yield more information simultaneously than conventional ultrafast spectroscopic techniques.

Hooper, Robynne; Zhou, Xibin; Li, Wen; Wagner, Nick; Kapteyn, Henry; Murnane, Margaret

2007-06-01

267

Harmonic and Anharmonic Properties of Diamond Structure Crystals with Application to the Calculation of the Thermal Expansion of Silicon. Ph.D. Thesis. Final Report  

NASA Technical Reports Server (NTRS)

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.

Wanser, K. H.

1981-01-01

268

Vibrational spectroscopic and DFT calculation studies of 2-amino-7-bromo-5-oxo-[1]benzopyrano [2,3-b]pyridine-3 carbonitrile  

NASA Astrophysics Data System (ADS)

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.

Premkumar, S.; Jawahar, A.; Mathavan, T.; Kumara Dhas, M.; Milton Franklin Benial, A.

2015-03-01

269

Vibrational spectroscopic and DFT calculation studies of 2-amino-7-bromo-5-oxo-[1]benzopyrano [2,3-b]pyridine-3 carbonitrile.  

PubMed

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. PMID:25498822

Premkumar, S; Jawahar, A; Mathavan, T; Kumara Dhas, M; Milton Franklin Benial, A

2015-03-01

270

Modeling of the influence of conformation, isotopic substitution, and aqueous environment on the vibrational spectrum of L-glutamic acid  

NASA Astrophysics Data System (ADS)

Quantum-mechanical calculations of optimized structures, harmonic force fields, and vibrational spectra were performed for 10 L-glutamic acid conformers. The vibrational spectra were interpreted using B3LYP/6-31+G** calculations for the stablest conformer. Satisfactory agreement between the experimental and theoretical data was obtained. Vibrational frequency shifts caused by isotopic substitution of various types in the L-glutamic acid molecule were analyzed taking into account the conformational structure and the influence of water medium and molecule ionization. Isotopic tags are suggested that can be used in biochemical studies taking into account their special characteristics.

Dotsenko, G. S.; Kuramshina, G. M.; Pentin, Yu. A.

2010-07-01

271

Optimal geometries and harmonic vibrational frequencies of the global minima of water clusters (H2O)n, n = 2-6, and several hexamer local minima at the CCSD(T) level of theory  

NASA Astrophysics Data System (ADS)

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 (??) are smaller than the MP2 ones, due to the fact that CCSD(T) produces shorter elongations (?R) 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 -?? = s . ?R, 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.

Miliordos, Evangelos; Aprà, Edoardo; Xantheas, Sotiris S.

2013-09-01

272

MULTIMODE quantum calculations of vibrational energies and IR spectrum of the NO+(H2O) cluster using accurate potential energy and dipole moment surfaces  

NASA Astrophysics Data System (ADS)

A new, full (nine)-dimensional potential energy surface and dipole moment surface to describe the NO+(H2O) 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+(H2O) and NO+(D2O) complexes. Using the calculated ZPE the dissociation energies of the clusters are reported. Vibrational configuration interaction calculations of NO+(H2O) and NO+(D2O) 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+(H2O) 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.

Homayoon, Zahra

2014-09-01

273

Characterization of 1,5-dimethoxynaphthalene by vibrational spectroscopy (FT-IR and FT-Raman) and density functional theory calculations  

NASA Astrophysics Data System (ADS)

In this work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and natural bond orbital (NBO) analysis of 1,5-dimethoxynaphthalene. The optimized molecular structure, atomic charges, vibrational frequencies and natural bond orbital analysis of 1,5-dimethoxynaphthalene have been studied by performing DFT/B3LYP/6-31G(d,p) level of theory. The FTIR, FT-Raman spectra were recorded in the region of 4000-400 cm-1 and 3500-50 cm-1 respectively. The scaled wavenumbers are compared with the experimental values. The difference between the observed and scaled wavenumber values of the most fundamentals is very small. The formation of hydrogen bond was investigated in terms of the charge density by the NBO analysis. Natural Population Analysis (NPA) was used for charge determination in the title molecule. Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis were investigated using theoretical calculations.

Kandasamy, M.; Velraj, G.; Kalaichelvan, S.; Mariappan, G.

2015-01-01

274

Ab initio calculation of a global potential, vibrational energies, and wave functions for HCN/HNC, and a simulation of the (A-tilde)-(X-tilde) emission spectrum  

NASA Technical Reports Server (NTRS)

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.

Bowman, Joel M.; Gazdy, Bela; Bentley, Joseph A.; Lee, Timothy J.; Dateo, Christopher E.

1993-01-01

275

Calculation of Rotation-Vibration Energy Levels of the Water Molecule with Near-Experimental Accuracy Based on an ab Initio Potential Energy Surface  

NASA Astrophysics Data System (ADS)

A recently computed, high-accuracy ab initio Born-Oppenheimer (BO) potential energy surface (PES) for the water molecule is combined with relativistic, adiabatic, quantum electrodynamics, and, crucially, nonadiabatic corrections. Calculations of ro-vibrational levels are presented for several water isotopologues and shown to have unprecedented accuracy. A purely ab initio calculation reproduces some 200 known band origins associated with seven isotopologues of water with a standard deviation (?) of about 0.35 cm-1. Introducing three semiempirical scaling parameters, two affecting the BO PES and one controlling nonadiabatic effects, reduces ? below 0.1 cm-1. Introducing one further rotational nonadiabatic parameter gives ? better than 0.1 cm-1 for all observed ro-vibrational energy levels up to J = 25. We conjecture that the energy levels of closed-shell molecules with roughly the same number of electrons as water, such as NH3, CH4, and H3O+, could be calculated to this accuracy using an analogous procedure. This means that near-ab initio calculations are capable of predicting transition frequencies with an accuracy only about a factor of 5 worse than high resolution experiments.

Polyansky, Oleg L.; Ovsyannikov, Roman I.; Kyuberis, Aleksandra A.; Lodi, Lorenzo; Tennyson, Jonathan; Zobov, Nikolai F.

2013-10-01

276

General harmonic balance solution of a cracked rotor-bearing-disk system for harmonic and sub-harmonic analysis: Analytical and  

E-print Network

General harmonic balance solution of a cracked rotor-bearing-disk system for harmonic and sub Structural health monitoring Breathing crack model Cracked rotor Harmonic balance method a b s t r a c t The effect of crack depth of a rotor-bearing-disk system on vibration amplitudes and whirl orbit shapes

Butcher, Eric A.

277

Application of higher harmonic control to hingeless rotor systems  

NASA Technical Reports Server (NTRS)

A comprehensive analytical formulation has been dveloped to predict the vibratory hub loads of a helicopter rotor system in forward flight. The 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 obtained from a scaled model rotor. Results of a parametric study on a hingeless 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.

Nguyen, Khanh; Chopra, Inderjit

1990-01-01

278

Applications of higher harmonic control to hingeless rotor systems  

NASA Technical Reports Server (NTRS)

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.

Nguyen, Khanh; Chopra, Inderjit

1991-01-01

279

Nonperturbative vibrational energy relaxation effects on vibrational line shapes  

E-print Network

Nonperturbative vibrational energy relaxation effects on vibrational line shapes Shilong Yang quantum dynamics of solutes in a condensed phase is proposed to calculate linear and nonlinear vibrational rate are derived in Appendix A. The vibrational energy relaxation VER rate is negligible for slow

Cao, Jianshu

280

First-principles calculations of the mechanic and vibration properties of AgRE (RE = Ho, Er, Tm) intermetallic compounds under pressure  

NASA Astrophysics Data System (ADS)

First-principles calculations are used to investigate the structural, elastic and vibration properties of the binary intermetallic compounds AgRE (RE = Ho, Er, Tm) with a B2 (CsCl) structure using density functional theory. The calculated structural parameters, the bulk modulus and its derivative with respect to pressure are in good agreement with experimental and numerical data. Additionally, the negative energy of formation of AgRE (RE = Ho, Er, Tm) with a B2 structure is examined. The independent second order elastic constants and their related properties, which are essential for mechanical stability, are investigated under pressure (0–60 GPa). The phonon spectra and phonon density of states are also discussed. All calculated phonon modes for AgRE (RE = Ho, Er) are positive in the phonon dispersion diagrams.

Mogulkoc, Y.; Ciftci, Y. O.; Colakoglu, K.; Deligoz, E.

2015-02-01

281

Calculating excited state properties using Kohn-Sham density functional theory.  

PubMed

The accuracy of excited states calculated with Kohn-Sham density functional theory using the maximum overlap method has been assessed for the calculation of adiabatic excitation energies, excited state structures, and excited state harmonic and anharmonic vibrational frequencies for open-shell singlet excited states. The computed Kohn-Sham adiabatic excitation energies are improved significantly by post self-consistent field spin-purification, but remain too low compared with experiment with a larger error than time-dependent density functional theory. Excited state structures and vibrational frequencies are also improved by spin-purification. The structures show a comparable accuracy to time-dependent density functional theory, while the harmonic vibrational frequencies are found to be more accurate for the majority of vibrational modes. The computed harmonic vibrational frequencies are also further improved by perturbative anharmonic corrections, suggesting a good description of the potential energy surface. Overall, excited state Kohn-Sham density functional theory is shown to provide an efficient method for the calculation of excited state structures and vibrational frequencies in open-shell singlet systems and provides a promising technique that can be applied to study large systems. PMID:23425455

Hanson-Heine, Magnus W D; George, Michael W; Besley, Nicholas A

2013-02-14

282

The fictitious force method for efficient calculation of vibration from a tunnel embedded in a multi-layered half-space  

NASA Astrophysics Data System (ADS)

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.

Hussein, M. F. M.; François, S.; Schevenels, M.; Hunt, H. E. M.; Talbot, J. P.; Degrande, G.

2014-12-01

283

Synthesis, structural and vibrational investigation on 2-phenyl-N-(pyrazin-2-yl)acetamide combining XRD diffraction, FT-IR and NMR spectroscopies with DFT calculations  

NASA Astrophysics Data System (ADS)

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.

Lukose, Jilu; Yohannan Panicker, C.; Nayak, Prakash S.; Narayana, B.; Sarojini, B. K.; Van Alsenoy, C.; Al-Saadi, Abdulaziz A.

2015-01-01

284

Synthesis, structural and vibrational investigation on 2-phenyl-N-(pyrazin-2-yl)acetamide combining XRD diffraction, FT-IR and NMR spectroscopies with DFT calculations.  

PubMed

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

Lukose, Jilu; Yohannan Panicker, C; Nayak, Prakash S; Narayana, B; Sarojini, B K; Van Alsenoy, C; Al-Saadi, Abdulaziz A

2015-01-25

285

Extended aeroelastic analysis for helicopter rotors with prescribed hub motion and blade appended penduluum vibration absorbers  

NASA Technical Reports Server (NTRS)

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.

Bielawa, R. L.

1984-01-01

286

Three-photon absorption and vibrational spectroscopic study of 2-methylamino-5-chlorobenzophenone.  

PubMed

In this paper, the vibrational spectral analysis and three-photon absorption properties of an organic material of 2-methylamino-5-chlorobenzophenone have been reported. The geometry and harmonic vibrational wavenumbers are calculated with the help of B3LYP density functional theory method. The detailed interpretation of the vibrational spectra has been carried out with the aid of normal coordinate analysis following the scaled quantum mechanical force field methodology (SQM). SQM force fields have also been used to calculate potential energy distribution (PED) in order to make conspicuous vibrational assignments. The nonlinear absorption properties have been investigated in ethanol solution at 532nm using the Z-scan technique employing laser pulses of 5ns duration. Open aperture Z-scan data reveal the presence of effective three-photon absorption for ns pulses at 532nm resulting in a strong optical limiting behavior, indicating possible photonic applications. PMID:23410921

Sajan, D; Chaitanya, K; Safakath, K; Philip, Reji; Suthan, T; Rajesh, N P

2013-04-01

287

X-ray crystal structure, vibrational spectra and DFT calculations of 3-chloro-7-azaindole: A case of dual N-H?N hydrogen bonds in dimers.  

PubMed

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)Å, ?=100.739(2)°, V=677.31(3)Å(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 (3500-60cm(-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 2500cm(-1), which is caused by multiple Fermi resonances between the N-H stretching vibration and various combinations bands. PMID:25315872

Morzyk-Ociepa, Barbara; Dysz, Karolina; Turowska-Tyrk, Ilona; Michalska, Danuta

2015-02-01

288

X-ray crystal structure, vibrational spectra and DFT calculations of 3-chloro-7-azaindole: A case of dual N-H⋯N hydrogen bonds in dimers  

NASA Astrophysics Data System (ADS)

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) Å, ? = 100.739(2)°, V = 677.31(3) Å3 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.

Morzyk-Ociepa, Barbara; Dysz, Karolina; Turowska-Tyrk, Ilona; Michalska, Danuta

2015-02-01

289

Vibrational dynamics of YPO4 and ScPO4 single crystals: An integrated study by polarized Raman spectroscopy and first-principles calculations  

NASA Astrophysics Data System (ADS)

A thorough study of the vibrational dynamics of xenotime YPO4 and its isomorphs, pretulite ScPO4 single crystals, with tetragonal zircon structure, was carried out by means of an integrated approach consisting of both polarized micro-Raman scattering spectroscopy and first-principles calculations. Polarized Raman scattering experiments were performed at room temperature either in the 180° or in the 90° geometry on both samples under different crystal orientations set by a micromanipulator. All the 12 independent components of the polarizability tensor, expected on the basis of the group theory for both YPO4 and ScPO4, were selected in turn and assigned in symmetry. In particular, it was possible to unambiguously identify a B1g mode peaked at 316 cm-1 in YPO4 and two B1g modes peaked at 350 and 677 cm-1 in ScPO4, respectively, all of them never reported before. These observations were corroborated by the results of first-principles calculations, based on density functional theory in the generalized gradient approximation, performed to determine Raman and infrared vibrational modes. In fact, an excellent agreement between computational and experimental results has been found.

Giarola, M.; Sanson, A.; Rahman, A.; Mariotto, G.; Bettinelli, M.; Speghini, A.; Cazzanelli, E.

2011-06-01

290

Theoretical calculation of the OH vibrational overtone spectra of 1-n alkane diols (n = 2-4): origin of disappearing hydrogen-bonded OH peak.  

PubMed

In this theoretical study, we simulated the vibrational overtone spectrum of ethylene glycol (EG), 1-3 propanediol (PD), and 1-4 butanediol (BD). Using the local mode model along with the potential energy curve and dipole moment function calculated by B3LYP/6-31+G(d,p) and QCISD/6-311++G(3df,3pd), we obtained the theoretical peak position and integrated absorption coefficient. Furthermore, the vibrational spectra was simulated using a Voigt function using homogeneous and inhomogenous width obtained from quantum chemical calculation methods. Previously, Howard and Kjaergaard recorded the second and third overtone photoacoustic spectra of the three aforementioned alkane diols in the gas phase and observed that the intramolecular hydrogen bonded OH peak becomes difficult to observe as the intramolecular hydrogen bonding strength increased, that is, as the chain length was increased. In this paper we show that the disappearance of the hydrogen-bonded OH peak for the OH stretching overtone excitation for BD is partly due to the increase in homogeneous width due to the increase in the hydrogen bond strength and partly due to the decrease in the relative population of the intramolecular hydrogen-bonded conformers as the chain length is increased. This latter feature is a consequence of the unfavorable strained geometry needed to form the intramolecular hydrogen bond in longer alkane chains. PMID:21568300

Cheng, Yu-Lung; Chen, Hui-Yi; Takahashi, Kaito

2011-06-01

291

Fan Flutter Computations Using the Harmonic Balance Method  

NASA Technical Reports Server (NTRS)

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.

Bakhle, Milind A.; Thomas, Jeffrey P.; Reddy, T.S.R.

2009-01-01

292

Electronic [UV-Visible] and vibrational [FT-IR, FT-Raman] investigation and NMR-mass spectroscopic analysis of terephthalic acid using quantum Gaussian calculations.  

PubMed

In this research work, the vibrational IR, polarization Raman, NMR and mass spectra of terephthalic acid (TA) were recorded. The observed fundamental peaks (IR, Raman) were assigned according to their distinctiveness region. The hybrid computational calculations were carried out for calculating geometrical and vibrational parameters by 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 molecular mass spectral data related to base molecule and substitutional group of the compound was analyzed. The modification of the chemical property by the reaction mechanism of the injection of dicarboxylic group in the base molecule was investigated. The (13)C and (1)H NMR spectra were simulated by using the gauge independent atomic orbital (GIAO) method and the absolute chemical shifts related to TMS were compared with experimental spectra. The study on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, were performed by hybrid Gaussian calculation methods. The orbital energies of different levels of HOMO and LUMO were calculated and the molecular orbital lobe overlapping showed the inter charge transformation between the base molecule and ligand group. From the frontier molecular orbitals (FMO), the possibility of electrophilic and nucleophilic hit also analyzed. The NLO activity of the title compound related to Polarizability and hyperpolarizability were also discussed. The present molecule was fragmented with respect to atomic mass and the mass variation depends on the substitutions have also been studied. PMID:25561302

Karthikeyan, N; Joseph Prince, J; Ramalingam, S; Periandy, S

2015-03-15

293

Anharmonic force field and vibrational dynamics of CH2F2 up to 5000 cm(-1) studied by Fourier transform infrared spectroscopy and state-of-the-art ab initio calculations.  

PubMed

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

Tasinato, Nicola; Regini, Giorgia; Stoppa, Paolo; Pietropolli Charmet, Andrea; Gambi, Alberto

2012-06-01

294

DENSITY FUNCTIONAL CALCULATION OF ENERGIES AND VIBRATIONAL FREQUENCIES OF GLUCOSE AND GLUCOSE-WATER COMPLEXES: WATER PLACEMENT AND GLUCOSE CONFORMATIONAL EFFECTS ON THE CALCULATED INFRARED SPECTRUM  

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...

295

Including slot harmonics to mechanical model of two-pole induction machine with a force actuator  

NASA Astrophysics Data System (ADS)

A simple mechanical model is identified for a two-pole induction machine that has a four-pole extra winding as a force actuator. The actuator can be used to suppress rotor vibrations. Forces affecting the rotor of the induction machine are separated into actuator force, purely mechanical force due to mass unbalance, and force caused by unbalanced magnetic pull from higher harmonics and unipolar flux. The force due to higher harmonics is embedded to the mechanical model. Parameters of the modified mechanical model are identified from measurements and the modifications are shown to be necessary. The force produced by the actuator is calculated using the mechanical model, direct flux measurements, and voltage and current of the force actuator. All three methods are shown to give matching results proving that the mechanical model can be used in vibration control. The test machine is shown to have time periodic behavior and discrete Fourier analysis is used to obtain time-invariant model parameters.

Sinervo, Anssi; Arkkio, Antero

2012-10-01

296

Empirical determination of the harmonic force constants in benzene. 4. The Fermi resonances.  

PubMed

In this article, we present a continuation of our work on the refinement of the harmonic force constants Fi,k in benzene (in symmetrized Whiffen's coordinates) and on a growing number of higher order (anharmonic) force constants, Fi,j,k and Fi,j,k,l, that are of importance for the benzene isotopomer invariant potential energy surface. The refined set of harmonic and anharmonic force constants improves the agreement between the experimental levels and those calculated theoretically. The emphasis of the present work is on the analysis of the two notable Fermi resonances in benzene (nu8 +nnu1 <=> (n +1)nu1 + nu6, where n = 0, 1, ... m, and nu20 <=> nu8 + nu19 <=> nu1 + nu6 + nu19). For this purpose, we have further extended our fully dimensional, fully symmetrized, and nonperturbative vibrational procedure to the vibrational structure of the benzene isotopic species with D6h symmetry. PMID:17181333

Rashev, Svetoslav; Moule, David C; Djambova, Svetlana T

2006-12-28

297

Ab-initio and DFT calculations on molecular structure, NBO, HOMO-LUMO study and a new vibrational analysis of 4-(Dimethylamino) Benzaldehyde.  

PubMed

The experimental and theoretical study on the molecular structure and a new vibrational analysis of 4-(Dimethylamino) Benzaldehyde (DMABA) is presented. The IR and Raman spectra were recorded in solid state. Optimized geometry, vibrational frequencies and various thermodynamic parameters of the title compound were calculated using DFT methods and are in agreement with the experimental values. A detailed interpretation of the IR and Raman spectra of the title compound were reported. The stability of the molecule arising from hyper-conjugative interactions and charge delocalization has been analyzed using NBO analysis and AIM approach. The HOMO and LUMO analysis were used to determine the charge transfer within the molecule and some molecular properties such as ionization potential, electron affinity, electronegativity, chemical potential, hardness, softness and global electrophilicity index. The TD-DFT approach was applied to assign the electronic transitions observed in the UV-visible spectrum measured experimentally. Molecular electrostatic potential map was performed by the DFT method. According to DSC measurements, the substance presents a melting point of 72.34°C and decomposes at temperatures higher than 193°C. PMID:25448963

Rocha, Mariana; Di Santo, Alejandro; Arias, Juan Marcelo; Gil, Diego M; Ben Altabef, Aída

2015-02-01

298

Vibrational spectroscopic studies (FT-IR, FT-Raman) and quantum chemical calculations on 5-(Adamantan-1-yl)-3-[(4-fluoroanilino)methyl]-2,3-dihydro-1,3,4-oxadiazole-2-thione, a potential chemotherapeutic agent  

NASA Astrophysics Data System (ADS)

The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments of 5-(Adamantan-1-yl)-3-[(4-fluoroanilino)methyl]-2,3-dihydro-1,3,4-oxadiazole-2-thione are investigated experimentally and theoretically using Gaussian09 software package. Potential energy distribution of normal modes vibrations was done using GAR2PED program. The HOMO and LUMO analysis are used to determine the charge transfer within the molecule. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. The calculated geometrical parameters are in agreement with the XRD data. The calculated first hyperpolarizability is high and the title compound is an attractive candidate for further studies in non-linear optical applications. To estimate the chemical reactivity of the molecule, the molecular electrostatic potential is calculated for the optimized geometry of the molecule.

Al-Abdullah, Ebtehal S.; Roseline, Sebastian S. H., Sr.; Al-Wabli, Reem I.; El-Emam, Ali A.; Panicker, C. Yohannan; Van Alsenoy, Christian

2014-12-01

299

Ab initio and DFT studies of the structure and vibrational spectra of anhydrous caffeine  

NASA Astrophysics Data System (ADS)

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.

Srivastava, Santosh K.; Singh, Vipin B.

2013-11-01

300

DFT computation and experimental analysis of vibrational and electronic spectra of phenoxy acetic acid herbicides  

NASA Astrophysics Data System (ADS)

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.

Arul Dhas, D.; Hubert Joe, I.; Roy, S. D. D.; Balachandran, S.

2013-05-01

301

Anharmonic vibrations of the dicarbon antisite defect in 4H-SiC  

SciTech Connect

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.

Yan, F.; Devaty, R. P.; Choyke, W. J. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Gali, A. [Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Kimoto, T. [Department of Electronic Science and Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510 (Japan); Ohshima, T. [Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan); Pensl, G. [Lehrstuhl fuer Angewandte Physik, Universitaet Erlangen-Nuernberg, Staudstr. 7/A3 Erlangen (Germany)

2012-03-26

302

The use of the SPASIBA spectroscopic potential for reproducing the structures and vibrational frequencies of a sries of acids: acetic acid, pivalic acid, succinic acid, adipic acid and ?-glutamic acid  

NASA Astrophysics Data System (ADS)

Normal coordinate analyses have been performed on acetic, pivalic, succinic and adipic acid dimers (including their deutero analogues) and the L-glutamic acid dimer. It is shown that the calculated potential energy surfaces and harmonic vibrational frequencies are in very good accordance with the experimental results. For all the observed vibrational modes below 1750 cm -1, the standard deviation between the 381 calculated and observed frequencies is approximately 12 cm -1. Comparison with previous assignments underlines a quasi-agreement for the four former molecules. In contrast, new assignments are given for some vibrational bands of L-glutamic acid.

Chhiba, M.; Derreumaux, P.; Vergoten, G.

1994-01-01

303

Molecular structure, IR spectra of 2-mercaptobenzothiazole and 2-mercaptobenzoxazole by density functional theory and ab initio Hartree-Fock calculations  

NASA Astrophysics Data System (ADS)

Quantum chemistry calculations have been performed using Gaussian03 program to compute optimized geometry, harmonic vibrational frequency along with intensities in IR and Raman spectra and atomic charges at RHF/6-31+G*, B3LYP/6-31+G* and B3LYP/6-31++G* levels for 2-mercaptobenzothiazole (MBT, C 7H 5NS 2) and 2-mercaptobenzoxazole (MBO, C 7H 5NOS) in the ground state. The scaled harmonic vibrational frequencies have been compared with experimental FT-IR and FT-Raman spectra. The results show that the scaled theoretical vibrational frequencies is very good agreement with the experimental values. A detailed interpretation of the infrared and Raman spectra of 2-mercaptobenzothiazole and 2-mercaptobenzoxazole was reported. Comparison of calculated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.

Li, Xiao-Hong; Tang, Zheng-Xin; Zhang, Xian-Zhou

2009-09-01

304

Molecular structure, IR spectra of 2-mercaptobenzothiazole and 2-mercaptobenzoxazole by density functional theory and ab initio Hartree-Fock calculations.  

PubMed

Quantum chemistry calculations have been performed using Gaussian03 program to compute optimized geometry, harmonic vibrational frequency along with intensities in IR and Raman spectra and atomic charges at RHF/6-31+G*, B3LYP/6-31+G* and B3LYP/6-31++G* levels for 2-mercaptobenzothiazole (MBT, C(7)H(5)NS(2)) and 2-mercaptobenzoxazole (MBO, C(7)H(5)NOS) in the ground state. The scaled harmonic vibrational frequencies have been compared with experimental FT-IR and FT-Raman spectra. The results show that the scaled theoretical vibrational frequencies is very good agreement with the experimental values. A detailed interpretation of the infrared and Raman spectra of 2-mercaptobenzothiazole and 2-mercaptobenzoxazole was reported. Comparison of calculated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. PMID:19553157

Li, Xiao-Hong; Tang, Zheng-Xin; Zhang, Xian-Zhou

2009-09-15

305

A vibrational molecular force field of model compounds with biological interest. V. Harmonic dynamic of N-acetyl-?- D-glucosamine in the crystalline state  

NASA Astrophysics Data System (ADS)

Combining the modified Urey—Bradley—Shimanouchi 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.

Kouach-Alix, I.; Vergoten, G.

1994-07-01

306

Molecular vibrational investigation [FT-IR, FT-Raman, UV-Visible and NMR] on Bis(thiourea) Nickel chloride using HF and DFT calculations.  

PubMed

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

Anand, S; Sundararajan, R S; Ramachandraraja, C; Ramalingam, S; Durga, R

2015-03-01

307

DFT study of structure and vibrational spectra of ceramide 3: comparison to experimental data  

Microsoft Academic Search

The Fourier transform Raman and infrared (IR) spectra of the Ceramide 3 (CER3) have been recorded in the regions 200–3500 cm and 680–4000 cm, respectively. We have calculated the equilibrium geometry, harmonic vibrational wavenumbers, electrostatic potential surfaces, absolute Raman scattering activities and IR absorption intensities by the density functional theory with B3LYP functionals having extended basis set 6-311G. This work is undertaken

Soni Mishra; Poonam Tandon

2012-01-01

308

Dynamic Analysis of Wind Turbine Planetary Gears Using an Extended Harmonic Balance Approach: Preprint  

SciTech Connect

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.

Guo, Y.; Keller, J.; Parker, R. G.

2012-06-01

309

Analysis of vibrational-translational energy transfer using the direct simulation Monte Carlo method  

NASA Technical Reports Server (NTRS)

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.

Boyd, Iain D.

1991-01-01

310

Experimental and computational study on molecular structure and vibrational analysis of an antihyperglycemic biomolecule: Gliclazide  

NASA Astrophysics Data System (ADS)

In present study, the experimental and theoretical harmonic vibrational frequencies of gliclazide molecule have been investigated. The experimental FT-IR (400-4000 cm-1) and Laser-Raman spectra (100-4000 cm-1) of the molecule in the solid phase were recorded. Theoretical vibrational frequencies and geometric parameters (bond lengths and bond angles) have been calculated using ab initio Hartree Fock (HF), density functional theory (B3LYP hybrid function) methods with 6-311++G(d,p) and 6-31G(d,p) basis sets by Gaussian 09W program. The assignments of the vibrational frequencies were performed by potential energy distribution (PED) analysis by using VEDA 4 program. Theoretical optimized geometric parameters and vibrational frequencies have been compared with the corresponding experimental data, and they have been shown to be in a good agreement with each other. Also, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies have been found.

Karakaya, Mustafa; Kürekçi, Mehmet; Eskiyurt, Buse; Sert, Yusuf; Ç?rak, Ça?r?

2015-01-01

311

The effective damping approach to design a dynamic vibration absorber using Coriolis force  

NASA Astrophysics Data System (ADS)

In this paper, the vibration reduction of a pendulum structure with dynamic vibration absorber (DVA) using Coriolis force is investigated. When the pendulum structure is subjected to a single harmonic excitation, the effective damping of Coriolis force is used with the second-order approximations to obtain the closed forms of optimal parameters of the DVA. The closed forms obtained show that the natural frequency of the absorber should be tuned to twice that of the pendulum. The closed forms of optimal parameters are verified by numerical optimization. The modified forms of optimal parameters are proposed to be used in case of general excitation. Base on this modified form, the design procedure is demonstrated by the numerical calculation of the free vibration and wind-induced vibration of a ropeway gondola.

Viet, L. D.; Anh, N. D.; Matsuhisa, H.

2011-04-01

312

Vibrational spectra and normal coordinate analysis of plant growth regulator 1-naphthalene acetamide.  

PubMed

FT Raman and IR spectra of the biologically active molecule, 1-naphthalene acetamide (NA) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers of NA have been calculated with the help of B3LYP density functional theory (DFT) method. 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 downshifting of NH(2) stretching wavenumber indicates the formation of intermolecular N-Hcdots, three dots, centeredO hydrogen bonding. The NBO analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule. PMID:20047855

Ravikumar, C; Padmaja, L; Hubert Joe, I

2010-02-01

313

Vibrational Schroedinger Cats  

NASA Technical Reports Server (NTRS)

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.

Kis, Z.; Janszky, J.; Vinogradov, An. V.; Kobayashi, T.

1996-01-01

314

Gearbox vibration diagnostic analyzer  

NASA Technical Reports Server (NTRS)

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.

1992-01-01

315

Method and apparatus for vibrating a substrate during material formation  

DOEpatents

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.

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

316

Application of Vibrational Spectroscopy Supported by Theoretical Calculations in Identification of Amorphous and Crystalline Forms of Cefuroxime Axetil  

PubMed Central

FT-IR and Raman scattering spectra of cefuroxime axetil were proposed for identification studies of its crystalline and amorphous forms. An analysis of experimental spectra was supported by quantum-chemical calculations performed with the use of B3LYP functional and 6-31G(d,p) as a basis set. The geometric structure of a cefuroxime axetil molecule, HOMO and LUMO orbitals, and molecular electrostatic potential were also determined by using DFT (density functional theory). The benefits of applying FT-IR and Raman scattering spectroscopy for characterization of drug subjected to degradation were discussed. PMID:25654137

Lewandowska, Kornelia; Jeli?ska, Anna; Zalewski, Przemys?aw; Oszczapowicz, Irena; Sikora, Adam; Kozak, Maciej

2015-01-01

317

Vibrational properties and DFT calculations of the perovskite metal formate framework of [(CH3)2NH2][Ni(HCOO3)] system.  

PubMed

Experimental Raman and IR spectra of multiferroic [(CH3)2NH2][Ni(HCOO)3] were recorded at room temperature. The three-parameter hybrid B3LYP density functional method has been used with the 6-31G(d, p) basis set to derive the equilibrium geometry, atomic spin densities, vibrational wavenumbers, infrared intensities and Raman scattering activities. Based on these calculations, the assignment of the observed bands to the respective internal and lattice modes is proposed. The performed calculations revealed that the ?(NH2) stretching, ?(NH2) rocking and ?(CH3) torsional modes are very sensitive to formation of the hydrogen bond between the DMA(+) cation and Ni-formate framework. Therefore, these modes are suitable probes for strength of hydrogen bonds in this family of metal-formate frameworks and study of their temperature dependence may provide significant information on a role of the hydrogen bonds in mechanism of the ferroelectric phase transition occurring in these compounds at low temperatures. PMID:24694997

M?czka, M; Zierkiewicz, W; Michalska, D; Hanuza, J

2014-07-15

318

Vibration manual  

NASA Technical Reports Server (NTRS)

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.

Green, C.

1971-01-01

319

Vibrational Thermodynamics of Materials Brent Fultz  

E-print Network

Vibrational Thermodynamics of Materials Brent Fultz California Institute of Technology, W. M. Keck Laboratory, Pasadena CA 91125 USA July 6, 2009 Abstract. The literature on vibrational thermodynamics of harmonic phonons in alloys are organized into thermodynamic models for unmixing and ordering

Fultz, Brent

320

Prediction of the fundamental vibrational frequencies for C{sub 60} by local density functional theory  

SciTech Connect

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.

Dixon, D.A.; Chase, B.E. [DuPont Central Research and Development, Wilmington, DE (United States); Fitzgerald, G. [Cray Research, Eagan, MN (United States); Matsuzawa, Nobuyuki [Sony Corporation Research Center, Yokohama (Japan)

1995-03-30

321

The Effect of Anharmonicity on Diatomic Vibration; A Spreadsheet Simulation  

NSDL National Science Digital Library

Instructors and students can use this spreadsheet to quickly and easily observe how the shape of a one-dimensional vibrational potential energy curve and its associated vibrational quantum energy levels depend on the anharmonicity. This illustrates the connection between the harmonic (approximation) and anharmonic descriptions of molecular vibrations.

322

Aeroelastic Computations of a Compressor Stage Using the Harmonic Balance Method  

NASA Technical Reports Server (NTRS)

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.

Reddy, T. S. R.

2010-01-01

323

Investigation of a vibration-damping unit for reduction in low-frequency vibrations of electric motors  

NASA Technical Reports Server (NTRS)

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.

Grigoryey, N. V.; Fedorovich, M. A.

1973-01-01

324

Measurement and analysis of the infrared absorption spectrum of the radical cation of [34](1, 2, 4, 5)cyclophane: Observation of electron-molecular vibration interaction between two benzene moieties  

NASA Astrophysics Data System (ADS)

A high-quality infrared absorption spectrum has been observed for the radical cation of [34](1, 2, 4, 5)cyclophane in a dichloromethane solution by using a Fourier-transform infrared spectrometer contained in an inert gas glovebox system. The structures and vibrational properties (harmonic frequencies, vibrational modes, and infrared intensities) have been calculated for the neutral species and radical cation of [34](1, 2, 4, 5)cyclophane by density functional theory at the B3LYP/6-311+G(d,p) level. The observed infrared spectra of the neutral species and radical cation are in good agreement with those calculated. Some specific vibrational modes of the radical cation have large infrared absorption intensities. The origin of the large infrared absorption intensities characteristic of the radical cation is discussed in terms of electron-molecular vibration interaction (changes in electronic structure induced by specific normal vibrations) between two benzene moieties of [34](1, 2, 4, 5)cyclophane.

Sakamoto, Akira; Tanaka, Nobuki; Shinmyozu, Teruo

2013-06-01

325

Vibrations and reorientations of NH3 molecules in [Mn(NH3)6](ClO4)2 studied by infrared spectroscopy and theoretical (DFT) calculations.  

PubMed

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 3385cm(-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 4.5kJmol(-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 TC(c)=137.6K (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. PMID:25459713

Hetma?czyk, Joanna; Hetma?czyk, Lukasz; Migda?-Mikuli, Anna; Mikuli, Edward

2014-10-24

326

Vibrations and reorientations of NH3 molecules in [Mn(NH3)6](ClO4)2 studied by infrared spectroscopy and theoretical (DFT) calculations  

NASA Astrophysics Data System (ADS)

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.

Hetma?czyk, Joanna; Hetma?czyk, ?ukasz; Migda?-Mikuli, Anna; Mikuli, Edward

2015-02-01

327

Density-functional theory study of vibrational relaxation of CO stretching excitation on Si(100).  

PubMed

A first-principles theory is presented for calculating the lifetime of adsorbate vibrations on semiconductor or insulator surfaces, where dissipation of the vibrational energy to substrate phonons is the dominant relaxation mechanism. As an example, we study the stretching vibration of CO/Si(100), where a lifetime of 2.3 ns has been measured recently [K. Lass, X. Han, and E. Hasselbrink, J. Chem. Phys. 123, 051102 (2005)]. Density-functional theory (DFT) calculations for the local modes of the adsorbate, including their anharmonic coupling, are combined with force field calculations for the substrate phonons. Using the DFT-Perdew-Burke-Ernzerhof functional, we have determined the most stable adsorption site for CO on top of the lower Si atom of the Si surface dimer, the local normal modes of CO, and the multidimensional potential energy surface for the CO vibrations. The anharmonic stretching frequency of adsorbed CO obtained in DFT-PBE is 5% lower than the experimental value, while the B3LYP functional reproduces the CO stretching frequency with only 1.4% error. The coupling between the anharmonic vibrational modes and the phonon continuum is evaluated within first-order perturbation theory, and transition rates for the CO vibrational relaxation are calculated using Fermi's golden rule. The lifetime of 0.5 ns obtained with DFT-PBE is in qualitative agreement with experiment, while using vibrational frequencies from the B3LYP functional gives a much too long lifetime as compared to experiment. We find that the numerical value of the lifetime is very sensitive to the harmonic frequencies used as input to the calculation of the transition rate. An empirical adjustment of these frequencies yields excellent agreement between our theory and experiment. From these calculations we conclude that the most probable microscopic decay channel of the CO stretching mode is into four lateral shift/bending quanta and one phonon. PMID:19045365

Sakong, Sung; Kratzer, Peter; Han, Xu; Lass, Kristian; Weingart, Oliver; Hasselbrink, Eckart

2008-11-01

328

Harmonic engine  

DOEpatents

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.

Bennett, Charles L. (Livermore, CA)

2009-10-20

329

Structure and vibrational analysis of methyl 3-amino-2-butenoate  

NASA Astrophysics Data System (ADS)

The molecular structure and vibrational spectra of methyl 3-(amino)-2-butenoate (MAB) and its deuterated analogous, D3MAB, were investigated using density functional theory (DFT) calculations. The geometrical parameters and harmonic vibrational wavenumbers of MAB and D3MAB were obtained at the B3LYP/6-311++G(d,p) level. The calculated vibrational wavenumbers were compared with the corresponding experimental results. The assignment of the IR and Raman spectra of MAB and D3MAB was facilitated by calculating the anharmonic wavenumbers at the B3LYP/6-311G(d,p) level as well as recording and calculating the MAB spectra in CCl4 solution. The assigned normal modes were compared with a similar molecule, 4-amino-3-penten-2-one (APO). The theoretical results were in good agreement with the experimental data. All theoretical and experimental results indicate that substitution of a methyl group with a methoxy group considerably weakens the intramolecular hydrogen bond and reduces the ?-electron delocalization in the chelated ring system. The IR spectra also indicate that in the solid state, MAB is not only engaged in an intramolecular hydrogen bond, but also forms an intermolecular hydrogen bond. However, the intermolecular hydrogen bond will be removed in dilute CCl4 solution.

Berenji, Ali Reza; Tayyari, Sayyed Faramarz; Rahimizadeh, Mohammad; Eshghi, Hossein; Vakili, Mohammad; Shiri, Ali

2013-02-01

330

Molecular structure, vibrational spectroscopy, NBO and HOMO, LUMO studies of o-methoxybenzonitrile  

NASA Astrophysics Data System (ADS)

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).

Elanthiraiyan, M.; Jayasudha, B.; Arivazhagan, M.

2015-01-01

331

Heat load tests of superconducting magnets vibrated electromagnetically for the Maglev train  

Microsoft Academic Search

Superconducting magnets on Maglev trains vibrate due to harmonic ripples of electromagnetic flux generated by ground coils. Heat load caused by vibration in the magnet amounted to several tens of watts in the electromagnetic vibration test. This was mainly because a.c. loss was induced in the helium vessel housing the superconducting coil, due to relative vibration between the aluminium thermal

J. Ohmori; H. Nakao; T. Yamashita; Y. Sanada; M. Shudou; M. Kawai; M. Fujita; M. Terai; A. Miura

1997-01-01

332

Coupled rotor/fuselage dynamic analysis of the AH-1G helicopter and correlation with flight vibrations data  

NASA Technical Reports Server (NTRS)

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.

Corrigan, J. C.; Cronkhite, J. D.; Dompka, R. V.; Perry, K. S.; Rogers, J. P.; Sadler, S. G.

1989-01-01

333

Free vibrations of delaminated beams  

NASA Technical Reports Server (NTRS)

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.

Shen, M.-H. H.; Grady, J. E.

1992-01-01

334

Comparison of subdominant gravitational wave harmonics between post-Newtonian and numerical relativity calculations and construction of multi-mode hybrids  

E-print Network

Gravitational waveforms which describe the inspiral, merger and ringdown of coalescing binaries are usually constructed by synthesising information from perturbative descriptions, in particular post-Newtonian theory and black-hole perturbation theory, with numerical solutions of the full Einstein equations. In this paper we discuss the "glueing" of numerical and post-Newtonian waveforms to produce hybrid waveforms which include subdominant spherical harmonics ("higher order modes"), and focus in particular on the process of consistently aligning the waveforms, which requires a comparison of both descriptions and a discussion of their imprecisions. We restrict to the non-precessing case, and illustrate the process using numerical waveforms of up to mass ratio $q=18$ produced with the BAM code, and publicly available waveforms from the SXS catalogue. The results also suggest new ways of analysing finite radius errors in numerical simulations.

Bustillo, Juan Calderón; Husa, Sascha; Sintes, Alicia M; Hannam, Mark; Pürrer, Michael

2015-01-01

335

Accurate potential energy, dipole moment curves, and lifetimes of vibrational states of heteronuclear alkali dimers  

SciTech Connect

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 Schrödinger 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.

Fedorov, Dmitry A.; Varganov, Sergey A., E-mail: svarganov@unr.edu [Department of Chemistry, University of Nevada, Reno, 1664 N. Virginia St., Reno, Nevada 89557-0216 (United States); Derevianko, Andrei [Department of Physics, University of Nevada, Reno, 1664 N. Virginia St., Reno, Nevada 89557-0220 (United States)] [Department of Physics, University of Nevada, Reno, 1664 N. Virginia St., Reno, Nevada 89557-0220 (United States)

2014-05-14

336

Active vibration control in Duffing mechanical systems using dynamic vibration absorbers  

NASA Astrophysics Data System (ADS)

This paper deals with the multi-frequency harmonic vibration suppression problem in forced Duffing mechanical systems using passive and active linear mass-spring-damper dynamic vibration absorbers. An active vibration absorption scheme is proposed to extend the vibrating energy dissipation capability of a passive dynamic vibration absorber for multiple excitation frequencies and, simultaneously, to perform reference position trajectory tracking tasks planned for the nonlinear primary system. A differential flatness-based disturbance estimation scheme is also described to estimate the unknown multiple time-varying frequency disturbance signal affecting the differentially flat nonlinear vibrating mechanical system dynamics. Some numerical simulation results are provided to show the efficient performance of the proposed active vibration absorption scheme and the fast estimation of the vibration disturbance signal.

Beltrán-Carbajal, F.; Silva-Navarro, G.

2014-07-01

337

Vibrational analysis of amino acids and short peptides in hydrated media. I. L-glycine and L-leucine.  

PubMed

Raman scattering and Fourier-transform infrared (FT-IR) attenuated transmission reflectance (ATR) spectra of two alpha-amino acids (alpha-AAs), i.e., glycine and leucine, were measured in H2O and D2O (at neutral pH and pD). This series of observed vibrational data gave us the opportunity to analyze vibrational features of both AAs in hydrated media by density functional theory (DFT) calculations at the B3LYP/6-31++G* level. Harmonic vibrational modes calculated after geometry optimization on the clusters containing each AA and 12 surrounding water molecules, which represent primary models for hydration scheme of amino acids, allowed us to assign the main observed peaks. PMID:17243664

Derbel, Najoua; Hernández, Belén; Pflüger, Fernando; Liquier, Jean; Geinguenaud, Frédéric; Jaïdane, Nejmeddine; Lakhdar, Zohra Ben; Ghomi, Mahmoud

2007-02-15

338

Analysis of potential helicopter vibration reduction concepts  

NASA Technical Reports Server (NTRS)

Results of analytical investigations to develop, understand, and evaluate potential helicopter vibration reduction concepts are presented in the following areas: identification of the fundamental sources of vibratory loads, blade design for low vibration, application of design optimization techniques, active higher harmonic control, blade appended aeromechanical devices, and the prediction of vibratory airloads. Primary sources of vibration are identified for a selected four-bladed articulated rotor operating in high speed level flight. The application of analytical design procedures and optimization techniques are shown to have the potential for establishing reduced vibration blade designs through variations in blade mass and stiffness distributions, and chordwise center-of-gravity location.

Landgrebe, A. J.; Davis, M. W.

1985-01-01

339

Experimental and theoretical debate on efficient second harmonic generation in Bis (Cinnamic acid): Hexamine cocrystal  

NASA Astrophysics Data System (ADS)

Second harmonic generation (SHG) in Bis (Cinnamic acid): Hexamine cocrystal was extensively analyzed through charge transfer (CT). The CT interactions through hydrogen bonding were well established with the aid of vibrational analysis and Natural Bond Orbital (NBO) analysis. The retentivity of coplanar nature of the cinnamic acid in the cocrystal was confirmed through UV-Visible spectroscopy and supported by Raman studies. Structural analysis indicated the quinoidal character of the given material presenting a high SHG efficiency. The first order hyperpolarizability value was calculated theoretically by density functional theory (DFT) and Hartree-Fock (HF) methods in support for the large value of SHG.

Vijayalakshmi, S.; Kalyanaraman, S.; Ravindran, T. R.

2014-02-01

340

Harmonic engine  

DOEpatents

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.

Bennett, Charles L.; Sewall, Noel; Boroa, Carl

2014-08-19

341

Estimation of Vibrational Frequencies and Vibrational Densities of States in Isotopically Substituted Nonlinear Triatomic Molecules  

E-print Network

Estimation of Vibrational Frequencies and Vibrational Densities of States in Isotopically for obtaining the unknown vibration frequencies of the many asymmetric isotopomers of a molecule from those In a number of recent calculations, we have required the vibrational densities of states of isotopically

Hathorn, Bryan C.

342

Nonlinear dynamic modeling and resonance tuning of Galfenol vibration absorbers  

NASA Astrophysics Data System (ADS)

This paper investigates the semi-active control of a magnetically-tunable vibration absorber’s resonance frequency. The vibration absorber that is considered is a metal-matrix composite containing the magnetostrictive material Galfenol (FeGa). A single degree of freedom model for the nonlinear vibration of the absorber is presented. The model is valid under arbitrary stress and magnetic field, and incorporates the variation in Galfenol’s elastic modulus throughout the composite as well as Galfenol’s asymmetric tension-compression behavior. Two boundary conditions—cantilevered and clamped-clamped—are imposed on the composite. The frequency response of the absorber to harmonic base excitation is calculated as a function of the operating conditions to determine the composite’s capacity for resonance tuning. The results show that nearly uniform controllability of the vibration absorber’s resonance frequency is possible below a threshold of the input power amplitude using weak magnetic fields of 0-8 kA m-1. Parametric studies are presented to characterize the effect on resonance tunability of Galfenol volume fraction and Galfenol location within the composite. The applicability of the results to composites of varying geometry and containing different Galfenol materials is discussed.

Scheidler, Justin J.; Dapino, Marcelo J.

2013-08-01

343

Uncertainties in scaling factors for ab initio vibrational frequencies.  

PubMed

Vibrational frequencies determined from ab initio calculations are often scaled by empirical factors. An empirical scaling factor partially compensates for the errors arising from vibrational anharmonicity and incomplete treatment of electron correlation. These errors are not random but are systematic biases. We report scaling factors for 40 combinations of theory and basis set, intended for predicting the fundamental frequencies from computed harmonic frequencies. An empirical scaling factor carries uncertainty. We quantify and report, for the first time, the uncertainties associated with the scaling factors. The uncertainties are larger than generally acknowledged; the scaling factors have only two significant digits. For example, the scaling factor for HF/6-31G(d) is 0.8982 +/- 0.0230 (standard uncertainty). The uncertainties in the scaling factors lead to corresponding uncertainties in predicted vibrational frequencies. The proposed method for quantifying the uncertainties associated with scaling factors is based on the Guide to the Expression of Uncertainty in Measurement, published by the International Organization for Standardization (ISO). The data used are from the Computational Chemistry Comparison and Benchmark Database (CCCBDB), maintained by the National Institute of Standards and Technology, which includes more than 3939 independent vibrations for 358 molecules. PMID:16834237

Irikura, Karl K; Johnson, Russell D; Kacker, Raghu N

2005-09-22

344

First-principle calculation and assignment for vibrational spectra of Ba(Mg{sub 1/3}Nb{sub 2/3})O{sub 3} microwave dielectric ceramic  

SciTech Connect

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 Ba–MgO{sub 6}/Ba–NbO{sub 6} on the a–b plane and the stretching vibrations of Ba–MgO{sub 6}/Ba–NbO{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.

Diao, Chuan-Ling [College of Physics and Electronics, Shandong Normal University, Jinan 250014 (China); State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871 (China); Wang, Chun-Hai; Lu, Jing [State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Luo, Neng-Neng; Jing, Xi-Ping, E-mail: sf751106@sina.com.cn, E-mail: xpjing@pku.edu.cn [State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871 (China); Qi, Ze-Ming; Shao, Tao; Wang, Yu-Yin [National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 (China); Wang, Quan-Chao; Kuang, Xiao-Jun; Fang, Liang [MOE Key Laboratory of New Processing Technology for Nonferrous Metals and Materials, College of Materials Science and Engineering, Guilin University of Technology, Guilin 541004 (China); Shi, Feng, E-mail: sf751106@sina.com.cn, E-mail: xpjing@pku.edu.cn [College of Physics and Electronics, Shandong Normal University, Jinan 250014 (China)

2014-03-21

345

Molecular docking, spectroscopic studies and quantum calculations on nootropic drug.  

PubMed

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

Uma Maheswari, J; Muthu, S; Sundius, Tom

2014-04-01

346

High-harmonic transient grating spectroscopy of NO2 electronic relaxation  

NASA Astrophysics Data System (ADS)

We study theoretically and experimentally the electronic relaxation of NO2 molecules excited by absorption of one ˜400 nm pump photon. Semiclassical simulations based on trajectory surface hopping calculations are performed. They predict fast oscillations of the electronic character around the intersection of the ground and first excited diabatic states. An experiment based on high-order harmonic transient grating spectroscopy reveals dynamics occurring on the same time scale. A systematic study of the detected transient is conducted to investigate the possible influence of the pump intensity, pump wavelength, and rotational temperature of the molecules. The quantitative agreement between measured and predicted dynamics shows that, in NO2, high harmonic transient grating spectroscopy encodes vibrational dynamics underlying the electronic relaxation.

Ruf, H.; Handschin, C.; Ferré, A.; Thiré, N.; Bertrand, J. B.; Bonnet, L.; Cireasa, R.; Constant, E.; Corkum, P. B.; Descamps, D.; Fabre, B.; Larregaray, P.; Mével, E.; Petit, S.; Pons, B.; Staedter, D.; Wörner, H. J.; Villeneuve, D. M.; Mairesse, Y.; Halvick, P.; Blanchet, V.

2012-12-01

347

Sunspots and Their Simple Harmonic Motion  

ERIC Educational Resources Information Center

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.

Ribeiro, C. I.

2013-01-01

348

Polyatomic molecule vibrations  

NASA Technical Reports Server (NTRS)

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.

1976-01-01

349

Vibration therapy.  

PubMed

Whole-body vibration training is a method for muscle strengthening that is increasingly used in a variety of clinical situations. Key descriptors of vibration devices include the frequency, the amplitude, and the direction of the vibration movement. In a typical vibration session, the user stands on the device in a static position or performs dynamic movements. Most authors hypothesize that vibrations stimulate muscle spindles and alpha-motoneurons, which initiate a muscle contraction. An immediate effect of a non-exhausting vibration session is an increase in muscle power. Most studies of the longer term use of vibration treatment in various disorders have pursued three therapeutic aims: increasing muscle strength, improving balance, and increasing bone mass. In a small pilot trial in children we noted improvements in standing function, lumbar spine bone mineral density, tibial bone mass, and calf muscle cross-sectional area. PMID:19740225

Rauch, Frank

2009-10-01

350

Vibrational spectroscopic study and NBO analysis on tranexamic acid using DFT method.  

PubMed

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

Muthu, S; Prabhakaran, A

2014-08-14

351

Vibrational spectroscopic study and NBO analysis on tranexamic acid using DFT method  

NASA Astrophysics Data System (ADS)

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.

Muthu, S.; Prabhakaran, A.

2014-08-01

352

Novel zinc(II) and copper(II) complexes of a Mannich base derived from lawsone: Synthesis, single crystal X-ray analysis, ab initio density functional theory calculations and vibrational analysis  

NASA Astrophysics Data System (ADS)

Zinc(II) and copper(II) complexes of a tridentate Mannich base L1 derived from 2-hydroxy-1,4-naphthoquinone, pyridinecarboxyaldehyde and 2-aminomethylpyridine, [ZnL1Cl2]·H2O 1 and [CuL1Cl2]·2H2O 2, have been synthesized and fully characterized. The structure of complex 1 has been elucidated by a single crystal X-ray diffraction study: the zinc atom is pentacoordinate and the coordination geometry is a distorted square base pyramid, with a geometric structural parameter ? equal to 0.149. Vibrational spectroscopy and ab initio DFT calculations of both compounds have confirmed that the two complexes exhibit similar structures. Full assignment of the vibrational spectra was also supported by careful analysis of the distorted geometries generated by the normal modes

Neves, Amanda P.; Vargas, Maria D.; Soto, Claudio A. Téllez; Ramos, Joanna M.; Visentin, Lorenzo do C.; Pinheiro, Carlos B.; Mangrich, Antônio S.; de Rezende, Edivaltrys I. P.

353

Novel zinc(II) and copper(II) complexes of a Mannich base derived from lawsone: Synthesis, single crystal X-ray analysis, ab initio density functional theory calculations and vibrational analysis.  

PubMed

Zinc(II) and copper(II) complexes of a tridentate Mannich base L1 derived from 2-hydroxy-1,4-naphthoquinone, pyridinecarboxyaldehyde and 2-aminomethylpyridine, [ZnL1Cl(2)]·H(2)O 1 and [CuL1Cl(2)]·2H(2)O 2, have been synthesized and fully characterized. The structure of complex 1 has been elucidated by a single crystal X-ray diffraction study: the zinc atom is pentacoordinate and the coordination geometry is a distorted square base pyramid, with a geometric structural parameter ? equal to 0.149. Vibrational spectroscopy and ab initio DFT calculations of both compounds have confirmed that the two complexes exhibit similar structures. Full assignment of the vibrational spectra was also supported by careful analysis of the distorted geometries generated by the normal modes. PMID:22513170

Neves, Amanda P; Vargas, Maria D; Téllez Soto, Claudio A; Ramos, Joanna M; Visentin, Lorenzo do C; Pinheiro, Carlos B; Mangrich, Antônio S; de Rezende, Edivaltrys I P

2012-08-01

354

Vibration response of misaligned rotors  

NASA Astrophysics Data System (ADS)

Misalignment is one of the common faults observed in rotors. Effect of misalignment on vibration response of coupled rotors is investigated in the present study. The coupled rotor system is modelled using Timoshenko beam elements with all six dof. An experimental approach is proposed for the first time for determination of magnitude and harmonic nature of the misalignment excitation. Misalignment effect at coupling location of rotor FE model is simulated using nodal force vector. The force vector is found using misalignment coupling stiffness matrix, derived from experimental data and applied misalignment between the two rotors. Steady-state vibration response is studied for sub-critical speeds. Effect of the types of misalignment (parallel and angular) on the vibration behaviour of the coupled rotor is examined. Along with lateral vibrations, axial and torsional vibrations are also investigated and nature of the vibration response is also examined. It has been found that the misalignment couples vibrations in bending, longitudinal and torsional modes. Some diagnostic features in the fast Fourier transform (FFT) of torsional and longitudinal response related to parallel and angular misalignment have been revealed. Full spectra and orbit plots are effectively used to reveal the unique nature of misalignment fault leading to reliable misalignment diagnostic information, not clearly brought out by earlier studies.

Patel, Tejas H.; Darpe, Ashish K.

2009-08-01

355

Geometries, singlet-triplet separations, dipole moments, ionization potentials, and vibrational frequencies in methylene (CH2) and halocarbenes (CHF, CF2, CCl2, CBr2, and CI2)  

NASA Astrophysics Data System (ADS)

The geometrical structure, harmonic vibrational frequencies, ionization potentials, and singlet-triplet gaps of simple substituted halocarbenes (CHF, CF2, CCl2, CBr2, and CI2) have been investigated by using the linear combination of Gaussian-type-orbital local-spin-density method. Optimized geometries, as well as vibrational frequencies, are in good agreement with available experimental data. The obtained values of singlet-triplet splittings (?EST) computed taking into account the nonlocal corrections are very close to experimental and previous theoretical investigations employing extended configuration interaction contributions. Many of the calculated properties obtained here have not yet been determined both experimentally and theoretically.

Russo, Nino; Sicilia, Emilia; Toscano, Marirosa

1992-10-01

356

Size-extensive vibrational self-consistent field method.  

PubMed

The vibrational self-consistent field (VSCF) method is a mean-field approach to solve the vibrational Schro?dinger equation and serves as a basis of vibrational perturbation and coupled-cluster methods. Together they account for anharmonic effects on vibrational transition frequencies and vibrationally averaged properties. This article reports the definition, programmable equations, and corresponding initial implementation of a diagrammatically size-extensive modification of VSCF, from which numerous terms with nonphysical size dependence in the original VSCF equations have been eliminated. When combined with a quartic force field (QFF), this compact and strictly size-extensive VSCF (XVSCF) method requires only quartic force constants of the ?(4)V/?Q(i)(2)?Q(j)(2) type, where V is the electronic energy and Q(i) is the ith normal coordinate. Consequently, the cost of a XVSCF calculation with a QFF increases only quadratically with the number of modes, while that of a VSCF calculation grows quartically. The effective (mean-field) potential of XVSCF felt by each mode is shown to be harmonic, making the XVSCF equations subject to a self-consistent analytical solution without matrix diagonalization or a basis-set expansion, which are necessary in VSCF. Even when the same set of force constants is used, XVSCF is nearly three orders of magnitude faster than VSCF implemented similarly. Yet, the results of XVSCF and VSCF are shown to approach each other as the molecular size is increased, implicating the inclusion of unnecessary, nonphysical terms in VSCF. The diagrams of the XVSCF energy expression and their evaluation rules are also proposed, underscoring their connected structures. PMID:21992283

Keçeli, Murat; Hirata, So

2011-10-01

357

Monte Carlo study of vibrational relaxation processes  

NASA Technical Reports Server (NTRS)

A new model is proposed for the computation of vibrational nonequilibrium in the direct simulation Monte Carlo method (DSMC). This model permits level to level vibrational transitions for the first time in a Monte Carlo flowfield simulation. The model follows the Landau-Teller theory for a harmonic oscillator in which the rates of transition are related to an experimental correlation for the vibrational relaxation time. The usual method for simulating such processes in the DSMC technique applies a constant exchange probability to each collision and the vibrational energy is treated as a continuum. A comparison of these two methods is made for the flow of nitrogen over a wedge. Significant differences exist for the vibrational temperatures computed. These arise as a consequence of the incorrect application of a constant exchange probability in the old method. It is found that the numerical performances of the two vibrational relaxation models are equal.

Boyd, Iain D.

1991-01-01

358

Coupled rotor/airframe vibration analysis  

NASA Technical Reports Server (NTRS)

A coupled rotor/airframe vibration analysis developed as a design tool for predicting helicopter vibrations and a research tool to quantify the effects of structural properties, aerodynamic interactions, and vibration reduction devices on vehicle vibration levels is described. The analysis consists of a base program utilizing an impedance matching technique to represent the coupled rotor/airframe dynamics of the system supported by inputs from several external programs supplying sophisticated rotor and airframe aerodynamic and structural dynamic representation. The theoretical background, computer program capabilities and limited correlation results are presented in this report. Correlation results using scale model wind tunnel results show that the analysis can adequately predict trends of vibration variations with airspeed and higher harmonic control effects. Predictions of absolute values of vibration levels were found to be very sensitive to modal characteristics and results were not representative of measured values.

Sopher, R.; Studwell, R. E.; Cassarino, S.; Kottapalli, S. B. R.

1982-01-01

359

An Accurate Quartic Force Field and Vibrational Frequencies for HNO and DNO  

NASA Technical Reports Server (NTRS)

An accurate ab initio quartic force field for HNO has been determined using the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations, CCSD(T), in conjunction with the correlation consistent polarized valence triple zeta (cc-pVTZ) basis set. Improved harmonic frequencies were determined with the cc-pVQZ basis set. Fundamental vibrational frequencies were determined using a second-order perturbation theory analysis and also using variational calculations. The N-0 stretch and bending fundamentals are determined well from both vibrational analyses. The H-N stretch, however, is shown to have an unusually large anharmonic correction, and is not well determined using second-order perturbation theory. The H-N fundamental is well determined from the variational calculations, demonstrating the quality of the ab initio quartic force field. The zero-point energy of HNO that should be used in isodesmic reactions is also discussed.

Dateo, Christopher E.; Lee, Timothy J.; Schwenke, David W.

1994-01-01

360

Vibrational C-H overtone spectroscopy and bond distances of butenes dissolved in liquid Xe  

NASA Astrophysics Data System (ADS)

Vibrational overtone spectra of isobutene, cis-2-butene, and trans-2-butene dissolved in liquid xenon at 163 K, have been recorded between 5000 and 16500 cm -1. Spectral regions for the first four overtones were measured using a Fourier transform spectrophotometer. The fifth overtone (? ? = 6) spectra were recorded with a double beam (pump-probe) thermal lens technique. Band deconvolution allowed isolation of individual transitions. Local-mode parameters were calculated for C-H oscillators in solution and compared with gas phase local-mode parameters. Density functional theory calculations were done to obtain C-H bond lengths and vibrational frequencies for the three butene isomers. Frequency shifts (? ?) with respect to gas phase results are attributed to changes in harmonic frequency and anharmonicity of the particular C-H bond of the sample dissolved in the inert liquid solvent.

Lopez-Calvo, Alfredo; Diez-y-Riega, Helena; Manzanares, Carlos E.

2009-10-01

361

Molecular vibrational states during a collision  

NASA Technical Reports Server (NTRS)

Alternative algebraic techniques to approximate a given Hamiltonian by a harmonic oscillator are described both for time-independent and time-dependent systems. We apply them to the description of a one dimensional atom-diatom collision. From the resulting evolution operator, we evaluate vibrational transition probabilities as well as other time-dependent properties. As expected, the ground vibrational state becomes a squeezed state during the collision.

Recamier, Jose A.; Jauregui, Rocio

1995-01-01

362

Good Vibrations  

NSDL National Science Digital Library

This lesson (on pages 15-24 of PDF) explores how sound is caused by vibrating objects. It explains that we hear by feeling vibrations passing through the air. Learners take part in several demonstrations, making those vibrations visible. They put a tuning fork in a shallow pan of water and use it to bounce a ping-pong ball, showing the fact that the tuning fork is vibrating when it's making a sound. There are extensions described involving comb kazoos, rubber band guitars, and putting rice or cereal on top of a drum.

2012-06-26

363

Vibrational dynamics of tricyanomethanide  

NASA Astrophysics Data System (ADS)

Steady-state and time resolved IR spectroscopy have been used to characterize vibrational spectra and relaxation dynamics of the antisymmetric CN stretching band of tricyanomethanide (TCM) in solutions of water, heavy water, methanol, dimethyl sulfoxide, formamide, and the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4]. The vibrational energy relaxation times for tricyanomethanide in these solvents are longer than those previously reported for dicyanamide, another CN containing anion, in the same solvents. Results of ab initio calculations of the vibrational frequencies for tricyanomethanide depend on the method used and compare favorably with experimentally measured values for IR-active and Raman-active bands. Proton and electron affinities were also calculated.

Weidinger, Daniel; Houchins, Cassidy; Owrutsky, Jeffrey C.

2012-02-01

364

Localized vibrational modes in Fermi liquids. General theory  

NASA Astrophysics Data System (ADS)

There exist an abundance of physically realized situations in atomic, chemical, molecular, nuclear, and solid-state physics which are modeled as a discrete state interacting with a continuum. One of these situations, a localized oscillator coupled to be the particle-hole excitation continuum of a Fermi liquid, forms the area of inquiry here. Special emphasis is placed on the electron-hole pair excitations of a metal, although the results are more general. In particular, an exactly soluble model, in which a localized harmonic oscillator is coupled to the pair-density fluctuations of a random-phase-approximation Fermi liquid by an interaction linear in both oscillator displacements and density operators, is considered. It is shown that this model is equivalent to a system of coupled harmonic oscillators, and, as such, the eigenstates are obtained via a straightforward normal-mode analysis. Expressions for the local spectral function of the oscillator are obtained in terms of level-shift and broadening functions which are evaluated in closed form in the density-of-states limit. Parametric calculations for vibrational line shapes are made, and the results are discussed in terms of "exponential-decay theory." The general results presented here have direct bearing in areas such as surface vibrational spectroscopy of adsorbed molecules, metal-hydride spectroscopy, and surface chemical-reactivity theory.

Gadzuk, J. W.

1981-08-01

365

High-order harmonic generation using intense femtosecond pulses  

NASA Astrophysics Data System (ADS)

Neon gas excited by 800-nm laser pulses (15 mJ, 125 fsec) at an intensity near 10 exp 15 W/sq cm generates harmonics up to the 109th order. The appearance of successively higher harmonics as the laser intensity is increased is compared to recent calculations of the strong-field atomic response. Blueshifting of the laser and harmonic wavelengths indicates a small degree of ionization until the threshold for the highest harmonics (above 91st) is reached.

Macklin, J. J.; Kmetec, J. D.; Gordon, C. L., III

1993-02-01

366

Vibrational, UV spectra, NBO, first order hyperpolarizability and HOMO-LUMO analysis of carvedilol  

NASA Astrophysics Data System (ADS)

In this work, we have investigated experimentally and theoretically on the molecular structure, vibrational spectra, UV spectral analysis and NBO studies of cardio-protective drug carvedilol. The FT-Raman and FT-IR spectra for carvedilol in the solid phase have been recorded in the region 4000-100 cm-1 and 4000-400 cm-1 respectively. Theoretical calculations were performed by using density functional theory (DFT) method at B3LYP/6-31G(d,p) and B3LYP/6-31++G(d,p) basis set levels. The harmonic vibrational frequencies, the optimized geometric parameters have been interpreted and compared with the reported experimental values. The complete vibrational assignments were performed on the basis of potential energy distribution (PED) of the vibrational modes. The thermodynamic properties and molecular electrostatic potential surfaces of the molecule were constructed. The electronic absorption spectrum was recorded in the region 400-200 nm and electronic properties such as HOMO and LUMO energies were calculated. The stability of the molecule arising from hyper conjugative interactions and charge delocalization have been analyzed from natural bond orbital (NBO) analysis. The first order hyperpolarizability of the title molecule was also calculated. The photo stability of carvedilol under different storage conditions were analyzed using UV-Vis spectral technique.

Swarnalatha, N.; Gunasekaran, S.; Nagarajan, M.; Srinivasan, S.; Sankari, G.; Ramkumaar, G. R.

2015-02-01

367

FT-IR spectroscopy in liquid xenon solution, ab initio calculations, normal coordinate analysis, and vibrational assignments of meso-2,4-dichloropentane and racemic-2,4-dichloropentane  

NASA Astrophysics Data System (ADS)

The infrared spectra of meso-2,4-dichloropentane and racemic-2,4-dichloropentane dissolved in liquid xenon have been obtained at 170 K in the range 400-4000 cm -1. The absorptions were observed with a low-temperature cell and a Fourier transform infrared spectrophotometer. The 2,4 dichloropentane sample was synthesized and its meso and racemic forms were separated with a spinning band distillation column. Ab initio molecular orbital calculations were performed on meso and racemic 2,4-dichloropentane to obtain the equilibrium geometry, vibrational frequencies, force fields, and infrared intensities. The calculations were done at the Hartree-Fock level using the 3-21G basis set. The Cartesian force fields from ab initio calculations have been converted to the force field in symmetry coordinates and scaled. Normal coordinate calculations were performed using a scaled quantum mechanical (SQM) force field. Potential energy distributions (PED) were also calculated. Vibrational normal modes of the most stable rotamer of symmetry C1 of meso-2,4-dichloropentane and the most stable rotamer of symmetry C2 of racemic 2,4-dichloropentane have been assigned to infrared absorption bands observed in liquid xenon solution. The assignments were based on calculated frequencies and PEDs. Variable temperature studies of the infrared spectrum of meso and racemic 2,4-dichloropentane dissolved in liquid argon were done between 165 and 195 K. Other rotamers could not be observed from the temperature dependent studies of the absorption band profile. The drastic decrease in the congestion of the spectra of the liquid xenon solution compared with the gas phase, room temperature spectra, combined with the observed small frequency shifts, allows the determination of reliable band positions.

Mina-Camilde, Nairmen; Cedeño, David L.; Manzanares I, Carlos

1998-03-01

368

Vibrations in elemental amorphous semiconductors  

E-print Network

In this thesis calculations of the vibrational spectra appropriate to structural models of the elemental amorphous semiconductors a-Ge, a-As and a-Se are presented. Simple dynamical models, involving restoring forces for bond length and angle...

Meek, Peter Ernest

1977-06-17

369

Variational study on the vibrational level structure and IVR behavior of highly vibrationally excited S0 formaldehyde.  

PubMed

We perform large scale converged variational vibrational calculations on S(0) formaldehyde up to very high excess vibrational energies (E(v)), E(v)?17,000cm(-1), using our vibrational method, consisting of a specific search/selection/Lanczos iteration procedure. Using the same method we investigate the vibrational level structure and intramolecular vibrational redistribution (IVR) characteristics for various vibrational levels in this energy range in order to assess the onset of IVR. PMID:22185953

Rashev, Svetoslav; Moule, David C

2012-02-15

370

Forced vibration of liquid in elastic rectangular tank  

Microsoft Academic Search

Forced vibration of liquid in a partially filled rectangular tank with elastic walls is analyzed. The vibrations are enforced by the tank's harmonic translation and rotation. The side walls and\\/or the bottom are assumed to be deformable and perform flexural oscillations normal to their plane. The resultant force and moment are determined, maintaining the tank's dynamic equilibrium. General solutions are

A. Kornecki

1976-01-01

371

Variational study on the vibrational level structure and vibrational level mixing of highly vibrationally excited S? D?CO.  

PubMed

We perform converged high precision variational calculations to determine the frequencies of a large number of vibrational levels in S(0) D(2)CO, extending from low to very high excess vibrational energies. For the calculations we use our specific vibrational method (recently employed for studies on H(2)CO), consisting of a combination of a search/selection algorithm and a Lanczos iteration procedure. Using the same method we perform large scale converged calculations on the vibrational level spectral structure and fragmentation at selected highly excited overtone states, up to excess vibrational energies of ?17,000 cm(-1), in order to study the characteristics of intramolecular vibrational redistribution (IVR), vibrational level density and mode selectivity. PMID:22750345

Rashev, Svetoslav; Moule, David C; Rashev, Vladimir

2012-11-01

372

Good Vibrations  

NSDL National Science Digital Library

In this activity, learners experiment with their voices and noisemakers to understand the connections between vibrations and the sounds created by those vibrations. This resource includes three quick demonstration activities that can be used independently or as a group to introduce learners to the basic elements of sound.

OMSI

2004-01-01

373

Vibrational Coupling  

SciTech Connect

By homing in on the distribution patterns of electrons around an atom, a team of scientists team with Berkeley Lab's Molecular Foundry showed how certain vibrations from benzene thiol cause electrical charge to "slosh" onto a gold surface (left), while others do not (right). The vibrations that cause this "sloshing" behavior yield a stronger SERS signal.

None

2011-01-01

374

Vibration analysis of composite laminate plate excited by piezoelectric actuators.  

PubMed

Piezoelectric materials can be used as actuators for the active vibration control of smart structural systems. In this work, piezoelectric patches are surface bonded to a composite laminate plate and used as vibration actuators. A static analysis based on the piezoelectricity and elasticity is conducted to evaluate the loads induced by the piezoelectric actuators to the host structure. The loads are then employed to develop the vibration response of a simply supported laminate rectangular plate excited by piezoelectric patches subjected to time harmonic voltages. An analytical solution of the vibration response of a simply supported laminate rectangular plate under time harmonic electrical loading is obtained and compared with finite element results to validate the present approach. The effects of location and exciting frequency of piezoelectric actuators on the vibration response of the laminate plate are investigated through a parametric study. Numerical results show that modes can be selectively excited, leading to structural vibration control. PMID:23529121

Her, Shiuh-Chuan; Lin, Chi-Sheng

2013-01-01

375

Vibration Analysis of Composite Laminate Plate Excited by Piezoelectric Actuators  

PubMed Central

Piezoelectric materials can be used as actuators for the active vibration control of smart structural systems. In this work, piezoelectric patches are surface bonded to a composite laminate plate and used as vibration actuators. A static analysis based on the piezoelectricity and elasticity is conducted to evaluate the loads induced by the piezoelectric actuators to the host structure. The loads are then employed to develop the vibration response of a simply supported laminate rectangular plate excited by piezoelectric patches subjected to time harmonic voltages. An analytical solution of the vibration response of a simply supported laminate rectangular plate under time harmonic electrical loading is obtained and compared with finite element results to validate the present approach. The effects of location and exciting frequency of piezoelectric actuators on the vibration response of the laminate plate are investigated through a parametric study. Numerical results show that modes can be selectively excited, leading to structural vibration control. PMID:23529121

Her, Shiuh-Chuan; Lin, Chi-Sheng

2013-01-01

376

FT-IR, FT-Raman, NMR spectra, density functional computations of the vibrational assignments (for monomer and dimer) and molecular geometry of anticancer drug 7-amino-2-methylchromone  

NASA Astrophysics Data System (ADS)

Vibrational assignments for the 7-amino-2-methylchromone (abbreviated as 7A2MC) molecule using a combination of experimental vibrational spectroscopic measurements and ab initio computational methods are reported. The optimized geometry, intermolecular hydrogen bonding, first order hyperpolarizability and harmonic vibrational wavenumbers of 7A2MC have been investigated with the help of B3LYP density functional theory method. The calculated molecular geometry parameters, the theoretically computed vibrational frequencies for monomer and dimer and relative peak intensities were compared with experimental data. DFT calculations using the B3LYP method and 6-31 + G(d,p) basis set were found to yield results that are very comparable to experimental IR and Raman spectra. Detailed vibrational assignments were performed with DFT calculations and the potential energy distribution (PED) obtained from the Vibrational Energy Distribution Analysis (VEDA) program. Natural Bond Orbital (NBO) study revealed the characteristics of the electronic delocalization of the molecular structure. 13C and 1H NMR spectra have been recorded and 13C and 1H nuclear magnetic resonance chemical shifts of the molecule have been calculated using the gauge independent atomic orbital (GIAO) method. Furthermore, All the possible calculated values are analyzed using correlation coefficients linear fitting equation and are shown strong correlation with the experimental data.

Mariappan, G.; Sundaraganesan, N.

2014-04-01

377

Structure, vibrational spectrum, and energetics of the CH5(+) ion - A theoretical investigation  

NASA Technical Reports Server (NTRS)

Analytic derivative techniques are utilized to determine molecular geometries, vibration spectra, molecular force field, proton affinity, and energetics of clustering of protonated methane. It is observed that the geometries are gradient optimized, while the harmonic force fields and IR intensities are also determined analytically at the SCF level. It is determined that the frequency of the torsional model for rotation of the H2 about the pseudothreefold axis of the CH3(+) group is extremely low, and the proton affinity of CH4 is calculated as 129.0 kcal/mol.

Komornicki, Andrew; Dixon, David A.

1987-01-01

378

Lowest Energy Vibrational Modes of Nine Naphthalene Derivatives; Experiment and Theory  

NASA Astrophysics Data System (ADS)

FIR gas phase absorption spectra of nine naphthalene derivatives (azulene, quinoline, isoquinoline, biphenyl, diphenylmethane, bibenzyl, 2-, 3-, and 4-phenyltoluene) have been recorded at medium resolution (0.5 wn) using a Fourier transform Bruker IFS125 interferometer located on the AILES beamline of SOLEIL synchrotron. Assignments of these weak vibrational bands were performed using density-functional theory calculations carried out at the harmonic and anharmonic levels (B97-1/6-311G(d,p)). Molecular structure dependence of the FIR spectra is discussed based on the comparative study of several selected FIR modes.

Martin-Drumel, M. A.; Pirali, O.; Laquais, Y.; Falvo, C.; Parneix, P.; Brechignac, Ph.

2013-06-01

379

Temperature dependence of electronic eigenenergies in the adiabatic harmonic approximation  

NASA Astrophysics Data System (ADS)

The renormalization of electronic eigenenergies due to electron-phonon interactions (temperature dependence and zero-point motion effect) is important in many materials. We address it in the adiabatic harmonic approximation, based on first principles (e.g., density-functional theory), from different points of view: directly from atomic position fluctuations or, alternatively, from Janak's theorem generalized to the case where the Helmholtz free energy, including the vibrational entropy, is used. We prove their equivalence, based on the usual form of Janak's theorem and on the dynamical equation. We then also place the Allen-Heine-Cardona (AHC) theory of the renormalization in a first-principles context. The AHC theory relies on the rigid-ion approximation, and naturally leads to a self-energy (Fan) contribution and a Debye-Waller contribution. Such a splitting can also be done for the complete harmonic adiabatic expression, in which the rigid-ion approximation is not required. A numerical study within the density-functional perturbation theory framework allows us to compare the AHC theory with frozen-phonon calculations, with or without the rigid-ion approximation. For the two different numerical approaches without non-rigid-ion terms, the agreement is better than 7 ? eV in the case of diamond, which represent an agreement to five significant digits. The magnitude of the non-rigid-ion terms in this case is also presented, distinguishing specific phonon modes contributions to different electronic eigenenergies.

Poncé, S.; Antonius, G.; Gillet, Y.; Boulanger, P.; Laflamme Janssen, J.; Marini, A.; Côté, M.; Gonze, X.

2014-12-01

380

Potential energy surfaces for vibrating hexatomic molecules  

NASA Astrophysics Data System (ADS)

Extension of empirical methods enables potential energy model construction for a vibrating hexatomic molecule. Application of these methods yields a model potential energy function that describes intramolecular vibrational dynamics and spectra of glyoxal, (CHO)2. A functional form is chosen that aids in model development and promotes transferability. It features a simple, modular design, and consists of Morse interactions applied between all atomic pairs. The Morse recipe assists in model development by naturally defining efficient basis functions for representing vibrational states. Solution of a series of sub-problems provides model parameter value estimates by nonlinear least- squares fits to spectroscopic data. Model development proceeds in both rectilinear normal and curvilinear local coordinate sets, letting efficiency determine which circumstance favors one set over the other. For example, the uncoupled harmonic oscillator sub-problem is solved in normal coordinates, while the hindered rotational sub- problem with limited coupling is solved in curvilinear coordinates. Definitive model evaluation is achieved by solving variationally for the energy levels and states of the full vibrational Schrödinger equation, composed of the exact kinetic energy operator and the model potential function. In normal coordinates, both operator and basis are readily defined. In curvilinear coordinates, however, the complex analytic form of the J = 0 kinetic energy operator is derived. Due to careful coordinate selection, terms in the model describing hindered rotational motion separate out, thus promoting development of an excellent contracted basis set. The contracted basis is expanded in terms of Mathieu functions, which are found to provide a rapidly convergent basis for any general one-dimensional hindering problem. Imposing symmetry on the functions further improves the basis. The full vibrational analysis reveals that the Morse functional form is capable of describing stretch, bend, and, surprisingly, torsion motions. The model reproduces structural and spectroscopic data with reasonable accuracy. Although the full calculation is set up and solved far more easily in normal coordinates, large- amplitude states converge slowly and localized states are described poorly. Dramatically improved rates of convergence result when using curvilinear coordinates due to coordinate and basis customization.

Rempe, Susan Lynne Beamis

381

Large amplitude out-of-plane vibrations of 1,3-benzodioxole in the S0 and S1 states: an analysis of fluorescence and excitation spectra by ab initio calculations.  

PubMed

We report the analytical expressions of the two-dimensional potential energy surfaces (PES) spanned by the puckering and flapping vibrations in the S0 and S1 states of 1,3-benzodioxole (BDO). Both PES are obtained from S0 and S1 energies computed on a grid of 2500 molecular geometries at the CASPT2 level. Both the S0 and S1 PES are anharmonic, and the planar geometry corresponds to a barrier that separates two minima at nonplanar geometries along the puckering/flapping deformations. Eigenvalues and eigenvectors of the mixed puckering/flapping modes are calculated by the Meyer flexible model. Improved vibronic levels, in better agreement with the observed spectra, are obtained by suitably optimized CASPT2 surfaces. To assign the lower-energy (0-500 cm(-1)) portion of emission and absorption spectra, we evaluate the band intensities by estimating the Franck-Condon factors between the puckering/flapping eigenvectors of the S0 and S1 states. From these calculations, we obtain a satisfactory assignment of the ground state IR spectra and of the fluorescence excitation spectrum. Both assignments are supported by the analysis of the vibrational structures of several single vibronic level (SVL) fluorescence spectra. The successful interpretation of these spectra shows that the S0 and S1 PES that we derive for BDO are substantially correct. The barrier heights in the two states are similar: 125.7 and 190.4 cm(-1) in S0 and in S1, respectively. In S0, the barrier is associated essentially with the puckering motion. In S1, it involves to a considerable extent also the flapping coordinate, whose vibrational frequency is much lower in S1 than in S0. This fact introduces a substantial Duschinsky effect in the S0-S1 transitions of BDO. PMID:16833992

Emanuele, Emanuela; Orlandi, Giorgio

2005-07-28

382

Vibration by relativistic effects  

E-print Network

Relativity, time reversal invariance in mechanics and principle of causality can be in the bases of a type of vibration of the extensive objects. It is because, the detailed analysis of the relativistic movement of an extensive body entail that all the objects must have inherent a vibratory movement to their own size. Such effect does not happen when it works with point particles thus is not stranger who happens unnoticed in the traditional studies. Also we can find relation between the form of vibration of the extensive objects and the energy that calculates by quantum considerations.

Enrique Oradaz Romay

2005-12-23

383

The harmonic oscillator and nuclear physics  

NASA Technical Reports Server (NTRS)

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.

Rowe, D. J.

1993-01-01

384

Ultrasound Vibrometry Using Orthogonal Frequency Based Vibration Pulses  

PubMed Central

New vibration pulses are developed for shear wave generation in a tissue region with preferred spectral distributions for ultrasound vibrometry applications. The primary objective of this work is to increase the frequency range of detectable harmonics of the shear wave. The secondary objective is to reduce the required peak intensity of transmitted pulses that induce the vibrations and shear waves. Unlike the periodic binary vibration pulses, the new vibration pulses have multiple pulses in one fundamental period of the vibration. The pulses are generated from an orthogonal-frequency wave composed of several sinusoidal signals of which the amplitudes increase with frequency to compensate for higher loss at higher frequency in tissues. The new method has been evaluated by studying the shear wave propagation in in vitro chicken and swine liver. The experimental results show that the new vibration pulses significantly increase tissue vibration with a reduced peak ultrasound intensity, compared with the binary vibration pulses. PMID:24158291

Zheng, Yi; Yao, Aiping; Chen, Shigao; Urban, Matthew W.; Lin, Haoming; Chen, Xin; Guo, Yanrong; Chen, Ke; Wang, Tianfu; Chen, Shiping

2014-01-01

385

Improved continuous-time higher harmonic control using [Eta] [infinity] methods  

E-print Network

The helicopter is a versatile aircraft that can take-off and land vertically, hover efficiently, and maneuver in confined space. This versatility is enabled by the main rotor, which also causes undesired harmonic vibration ...

Fan, Frank H. (Frank Hsiao)

2013-01-01

386

Monitoring molecular dynamics using coherent electrons from high harmonic generation  

PubMed Central

We report a previously undescribed spectroscopic probe that makes use of electrons rescattered during the process of high-order harmonic generation. We excite coherent vibrations in SF6 using impulsive stimulated Raman scattering with a short laser pulse. A second, more intense laser pulse generates high-order harmonics of the fundamental laser, at wavelengths of ?20–50 nm. The high-order harmonic yield is observed to oscillate, at frequencies corresponding to all of the Raman-active modes of SF6, with an asymmetric mode most visible. The data also show evidence of relaxation dynamics after impulsive excitation of the molecule. Theoretical modeling indicates that the high harmonic yield should be modulated by both Raman and infrared-active vibrational modes. Our results indicate that high harmonic generation is a very sensitive probe of vibrational dynamics and may yield more information simultaneously than conventional ultrafast spectroscopic techniques. Because the de Broglie wavelength of the recolliding electron is on the order of interatomic distances, i.e., ?1.5 Å, small changes in the shape of the molecule lead to large changes in the high harmonic yield. This work therefore demonstrates a previously undescribed spectroscopic technique for probing ultrafast internal dynamics in molecules and, in particular, on the chemically important ground-state potential surface. PMID:16895984

Wagner, Nicholas L.; Wüest, Andrea; Christov, Ivan P.; Popmintchev, Tenio; Zhou, Xibin; Murnane, Margaret M.; Kapteyn, Henry C.

2006-01-01

387

Simple Harmonic Motion in Harmonic Plane Waves.  

ERIC Educational Resources Information Center

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)

Benumof, Reuben

1980-01-01

388

Vibrational genetic algorithm as a new concept in airfoil design  

Microsoft Academic Search

We introduce the Vibration concept for real coded Genetic Algorithm and its implementation to inverse airfoil design, which decreases the number of CFD calculations. This concept assures efficient diversity in the population and consequently gives faster solution. We used the Vibration concept as vibrational mutation and vibrational crossover. For the mutational manner, a sinusoidal wave with random amplitude is introduced

Abdurrahman Hacio?lu; ?brahim Özkol

2002-01-01

389

Vibrational anharmonicity and multilevel vibrational dephasing from vibrational echo beats  

E-print Network

Vibrational anharmonicity and multilevel vibrational dephasing from vibrational echo beats K. D 94305 Received 22 January 1997; accepted 21 March 1997 Vibrational echo experiments were performed the vibrational anharmonicities, leading to the excitation and dephasing of a multilevel coherence. From the beat

Fayer, Michael D.

390

Infrared spectra of permanganate anions in potassium perchlorate matrices: vibrational anharmonicity, effective symmetry and vibrational mode mixing effects  

NASA Astrophysics Data System (ADS)

Fourier transform infrared spectra of MnO 4- anions isomorphously isolated in potassium perchlorate matrices were recorded at room and low temperature (LT, ˜100 K). On the basis of the detected second-order vibrational transitions involving the dopant species ?3 mode components, anharmonicity constants and harmonic eigenvalues for these modes were calculated. Despite the fact that, rigorously speaking, the appearance of the spectra of dopant permanganate anions may be explained in terms of a Cs site symmetry, the ?3 stretching region resembles an approximate A1? E splitting (characteristic for a local C3 v or even higher symmetry), which is not expected, even within the latent symmetry approach. We explain such spectral patterns on the basis of vibrational mode mixing (a 'Fermi-like' resonance) of the MnO 4-?1 mode with the ?3a site-group component. With the results of degenerate case stationary perturbation theory, we show that in the present case the Fermi-like resonance is predominantly responsible for the observed spectral features. The appearance of the region of second-order vibrational transitions in the spectra of dopant permanganate anions may be better explained in terms of the (rigorous) crystallographic Cs site group (corresponding to the crystallographic Pnma space group), instead of the 'latent' (effective) symmetry site group C2 v (corresponding to the latent symmetry space group Imma).

Pejov, Ljup?o; Petruševski, Vladimir M.

2002-11-01

391

Additional calculations of triton moments  

NASA Astrophysics Data System (ADS)

The formalism of hyperspherical harmonics is used to calculate several moments of the triton photoeffect for a Volkov potential with Serber exchange. The accuracy of Clare's calculations of moments ?0 and ?1 is improved by including more terms in the hyperspherical harmonic expansion of the potential and of the ground state wave function. The moment ?2=8.9×104 MeV3 mb is calculated using one term in the hyperspherical harmonic expansions of the potential and wave function. We invert four moments and find reasonable agreement with Gorbunov's measurements of the 3He photoeffect. NUCLEAR REACTIONS Triton photoeffect, hyperspherical harmonics, moments of photoeffect, inversion of moments.

Lally, D. F.; Levinger, J. S.

1982-02-01

392

Polynomial Harmonic Morphisms Martin Svensson  

E-print Network

Polynomial Harmonic Morphisms Martin Svensson Examensarbete, 20 poang Lunds Universitet November Chapter 2. Harmonic Maps 13 1. The Second Fundamental Form 13 2. Harmonic Maps 18 3. Harmonic Functions 25 Chapter 3. Harmonic Morphisms 29 1. Horizontal Conformality 29 2. Harmonic Morphisms 33 3. The Existence

Gudmundsson, Sigmundur

393

Vibrational spectral analysis of anti-neurodegenerative drug Levodopa: A DFT study  

NASA Astrophysics Data System (ADS)

The Fourier transform Raman and infrared spectra of anti-neurodegenerative drug Levodopa (L-3,4-dihydroxy phenyl alanine) in crystalline form have been recorded and analyzed. The optimized geometry, intermolecular hydrogen bonding, and harmonic vibrational wavenumbers of Levodopa have been investigated with the help of B3LYP density functional theory method. The calculated molecular geometry has been compared with the experimental data. The assignments of the vibrational spectra have been carried out with the aid of normal co-ordinate analysis following the scaled quantum mechanical force field methodology. The strong doubly hydrogen bonded interface of the dimerized system is well demonstrated by the natural bond orbital analysis. The biological activity of substituents like carboxylic acid, hydroxyl groups of the catechol ring and amino group are evident from the hydrogen bonds through which the target amino acids are linked to the drug as evidenced from molecular docking.

Edwin, Bismi; Hubert Joe, I.

2013-02-01

394

Multicyclic control of a helicopter rotor considering the influence of vibration, loads, and control motion  

NASA Technical Reports Server (NTRS)

Weighted multiple linear regression is used to establish a transfer function matrix relationship between higher harmonic control inputs and transducer vibration outputs for a controllable twist rotor. Data used in the regression were taken from the test of a KAMAN controllable twist rotor conducted in the Ames Research Center's 40- by 80-Foot Wind Tunnel in June 1977. Optimal controls to minimize fixed system vibrational levels are calculated using linear quadratic regulatory theory with a control deflection penalty included in the performance criteria. Control sensitivity to changes in control travel, forward speed, and lift and propulsive forces is examined. It is found that the linear transfer matrix is a strong function of forward speed and a weak function of lift and propulsive force. An open-loop strategy is proposed for systems with limited control travel.

Brown, T. J.; Mccloud, J. L., III

1980-01-01

395

Enhancing tidal harmonic analysis: Robust (hybrid L1 ) solutions  

E-print Network

Enhancing tidal harmonic analysis: Robust (hybrid L1 =L2 ) solutions Keith E. Leffler Ã?, David A 24 February 2008 Accepted 28 April 2008 Keywords: Tides Tidal analysis Harmonic analysis Robust is calculated from the power spectrum of the residual, a calculation that filters broad spectrum noise

Jay, David

396

Harmonic power flow for unbalanced systems  

SciTech Connect

In this paper a harmonic power flow that analyzes harmonics in unbalanced systems is presented. The developed algorithm has two steps which are executed successively: the first is a fundamental frequency power flow for the ac linear network in which non-linear loads are represented by current sources. The second is a frequency-domain iterative Newton-Raphson method to calculate the harmonics generated by non-linear loads. In this second step, the ac linear network is represented by a generalized Thevenin equivalent with respect to the non-linear loads, obtained from the power flow solution. Both linear and non-linear loads are considered in terms of power.

Valcarcel, M.; Mayordomo, J.G. (Univ. Politecnica de Madrid (Spain). Dept. de Ingenieria Electrica)

1993-10-01

397

1,2-Diiododisilane and 1,1,2,2-tetraiododisilane: a reinvestigation of the molecular structures and vibrational properties by gas-phase electron diffraction, temperature dependent Raman spectroscopy, and ab initio molecular orbital- and density functional calculations  

NASA Astrophysics Data System (ADS)

The molecular structure, internal rotation and vibrational properties of 1,2-diiododisilane (DIDS), IH 2Si-SiH 2I, and 1,1,2,2-tetraiododisilane (TIDS), I 2HSi-SiHI 2, have been reinvestigated using gas phase electron diffraction (GED) data at temperatures of 55 (DIDS) and 155 (TIDS) °C, together with Raman spectroscopy, and ab initio molecular orbital (MO)- and density functional (DFT) calculations. The title compounds exist in the gas and liquid phases as a mixture of two conformers, anti ( C2 h), with a torsion angle ? (XSiSiX)=180°, and gauche ( C2), with a torsion angle ? (XSiSiX) ?60° (X=I (DIDS), X=H (TIDS)). Some structural parameter values obtained from the GED dynamic model refinements, using results from the theoretical calculations as constraints, were as follows ( anti values with estimated 2? uncertainties): For DIDS: Bond lengths ( rg): r(Si-Si)=2.315(26) Å, r(Si-I)=2.447(6) Å. Bond angles (? ?): ?SiSiI=107.5(10)°, ?ISiH=109.8(5)°. For TIDS: Bond lengths ( rg): r(Si-Si)=2.364(30) Å, r(Si-I)=2.450(6) Å, Bond angles (? ?): ?SiSiI=107.2(4)°, ?ISiH=109.9(2)°, ?ISiI=111.7(3)°. Raman vibrational spectra for various temperatures are presented and analysed aided by normal coordinate calculations and the ab initio MO- and DFT results. From intensity variations with temperature of four band pairs for DIDS and two pairs for TIDS, conformational energies in the liquids were determined from van't Hoff plots. ? H0(?? E0) values of 0.31±0.14 kcal mol -1 and 0.14±0.10 kcal mol -1 were obtained for DIDS and TIDS respectively, gauche being the low energy conformer for both disilanes.

Johansen, Tore H.; Hassler, Karl; Tekautz, Günter; Hagen, Kolbjørn

2001-12-01

398

Theoretical interpretation of the vibrational spectrum of bicyclo[1.1.0]butane in terms of an ab initio anharmonic model  

NASA Astrophysics Data System (ADS)

The anharmonic vibrational IR and Raman spectra of the bicyclo[1.1.0]butane molecule have been calculated in the range of up to 4000 cm-1 using a numerical and analytical realization of the van Vleck second-order operator perturbation theory. Cubic and quartic force constants in normal coordinates, as well as cubic surfaces of the dipole moment and polarizability, have been found by numerical differentiation of the corresponding first and second derivatives calculated by the MP2/cc-pVTZ quantum-mechanical method. In order to increase the prediction accuracy of vibrational transitions, corresponding harmonic frequencies have been obtained by the CCSD(T)/cc-pVTZ high-precision quantum mechanical method. The anharmonic intensities of the IR and Raman spectra have been calculated using canonical transformations of the operators of the dipole moment and polarizability expanded into a Taylor series around the equilibrium configuration. The assignment of experimental vibrational bands in the IR and Raman spectra has been analyzed. It has been shown that the anharmonic calculation based on the above-described procedure of combining more exact harmonic frequencies with the anharmonic force field obtained with a more economical method makes possible the reliable interpretation of the majority of spectral bands, including Fermi and Darling-Dennison resonances.

Berezin, K. V.; Nechaev, V. V.; Berezin, M. K.; Stepanov, N. F.; Krasnoshchekov, S. V.

2014-09-01

399

FT-IR, FT-Raman spectra, and DFT computations of the vibrational spectra and molecular geometry of chlorzoxazone.  

PubMed

Far-IR, mid-IR, and FT-Raman spectra of the chlorzoxazone (CZX) were recorded. The observed vibrational wavenumbers were analyzed and assigned to different normal modes of vibration of the molecule. Density functional calculations were performed to support wavenumber assignments of the observed bands. The equilibrium geometry and harmonic wavenumbers of CZX were calculated by the DFT B3LYP method. All tautomeric forms and dimer form of CZX were determined and optimized. Additionally, experimental FT-IR spectrum in ethanol solution was recorded and compared with solid phase experimental data for the first time. The combination of the DFT B3LYP with polarized continuum model (PCM) was employed to characterize the solvent effects in ethanol solution. PMID:24684869

Yurdakul, Senay; Yurdakul, Murat

2014-05-21

400

Applicability of density functional theory in reproducing accurate vibrational spectra of surface bound species.  

PubMed

The structural equilibrium parameters, the adsorption energies, and the vibrational frequencies of the nitrogen molecule and the hydrogen atom adsorbed on the (111) surface of rhodium have been investigated using different generalized-gradient approximation (GGA), nonlocal correlation, meta-GGA, and hybrid functionals, namely, Perdew, Burke, and Ernzerhof (PBE), Revised-RPBE, vdW-DF, Tao, Perdew, Staroverov, and Scuseria functional (TPSS), and Heyd, Scuseria, and Ernzerhof (HSE06) functional in the plane wave formalism. Among the five tested functionals, nonlocal vdW-DF and meta-GGA TPSS functionals are most successful in describing energetics of dinitrogen physisorption to the Rh(111) surface, while the PBE functional provides the correct chemisorption energy for the hydrogen atom. It was also found that TPSS functional produces the best vibrational spectra of the nitrogen molecule and the hydrogen atom on rhodium within the harmonic formalism with the error of -2.62 and -1.1% for the N-N stretching and Rh-H stretching frequency. Thus, TPSS functional was proposed as a method of choice for obtaining vibrational spectra of low weight adsorbates on metallic surfaces within the harmonic approximation. At the anharmonic level, by decoupling the Rh-H and N-N stretching modes from the bulk phonons and by solving one- and two-dimensional Schrödinger equation associated with the Rh-H, Rh-N, and N-N potential energy we calculated the anharmonic correction for N-N and Rh-H stretching modes as -31 cm(-1) and -77 cm(-1) at PBE level. Anharmonic vibrational frequencies calculated with the use of the hybrid HSE06 function are in best agreement with available experiments. PMID:25164265

Matanovi?, Ivana; Atanassov, Plamen; Kiefer, Boris; Garzon, Fernando H; Henson, Neil J

2014-10-01

401

Nuclear momentum distribution in solid and liquid HF from ab initio calculation.  

PubMed

A calculation of nuclear momentum distribution of liquid and solid hydrogen fluoride was performed. In both systems, density functional theory generalized gradient approximation functional of Perdew, Burke, and Ernzerhof was used for the calculation: for liquid hydrogen fluoride, using an atom centered basis set for an isolated molecule with optimized geometry, and for solid hydrogen fluoride using plane-wave basis sets on optimized orthorhombic crystal cell. For liquid hydrogen fluoride, a semiclassical approach was adopted with the vibrational contribution to momentum distribution obtained from the density functional theory calculation and translational and rotational contributions calculated classically. Nuclear momentum distribution in the solid hydrogen fluoride was calculated entirely quantum mechanically using phonon dispersion and vibrational density of states calculated in the framework of plane-wave density functional theory. Theoretical results were contrasted with recently obtained results of Compton (deep inelastic) neutron scattering on liquid and solid hydrogen fluoride. In case of liquid hydrogen fluoride, almost a perfect agreement between theory and experiment was achieved within the harmonic Born-Oppenheimer approximation. For the solid system under investigation, the harmonic approximation leads to small (4%) overestimation of the square root of the second moment indicating that neutron Compton scattering technique is sensitive to proton delocalization due to hydrogen bonding in solid hydrogen fluoride. PMID:20950015

Krzystyniak, M

2010-10-14

402

Free energy of a dumbbell interstitial defect in bcc Fe: Harmonic and anharmonic contributions  

Microsoft Academic Search

The stability of interstitial defect and dislocation structures in bcc Fe as a function of temperature is believed to play a crucial role in determining defect evolution under irradiation conditions. The vibrational properties of defects constitute one contribution to the corresponding energetics and much work has been done within the harmonic approximation to determine the vibrational formation free energy and

S. Chiesa; P. M. Derlet; S. L. Dudarev

2009-01-01

403

Conformational stability, vibrational and NMR analysis, chemical potential and thermodynamical parameter of 3-tert-butyl-4-hydroxyanisole.  

PubMed

The FT-IR and FT-Raman spectra of 3-tert-butyl-4-hydroxyanisole (TBHA) molecule have been recorded in the region 4000-400 cm(-1) and 3500-100 cm(-1), respectively. Optimized geometrical structure, harmonic vibrational frequencies has been computed by B3LYP level using 6-31G (d,p) and 6-311+G (d,p) basis sets. The observed FT-IR and FT-Raman vibrational frequencies are analyzed and compared with theoretically predicted vibrational frequencies. The geometries and normal modes of vibration obtained from DFT method are in good agreement with the experimental data. The Mulliken charges, the natural bonding orbital (NBO) analysis, the first-order hyperpolarizability of the investigated molecule were computed using DFT calculations. Besides, charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap, molecular electrostatic potential (MEP) were calculated and analyzed. The isotropic chemical shift computed by (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the TBHA calculated using the gauge invariant atomic orbital (GIAO) method also shows good agreement with experimental observations. PMID:25173520

Balachandran, V; Karpagam, V; Revathi, B; Kavimani, M; Santhi, G

2015-01-25

404

Conformational stability, vibrational and NMR analysis, chemical potential and thermodynamical parameter of 3-tert-butyl-4-hydroxyanisole  

NASA Astrophysics Data System (ADS)

The FT-IR and FT-Raman spectra of 3-tert-butyl-4-hydroxyanisole (TBHA) molecule have been recorded in the region 4000-400 cm-1 and 3500-100 cm-1, respectively. Optimized geometrical structure, harmonic vibrational frequencies has been computed by B3LYP level using 6-31G (d, p) and 6-311 + G (d, p) basis sets. The observed FT-IR and FT-Raman vibrational frequencies are analyzed and compared with theoretically predicted vibrational frequencies. The geometries and normal modes of vibration obtained from DFT method are in good agreement with the experimental data. The Mulliken charges, the natural bonding orbital (NBO) analysis, the first-order hyperpolarizability of the investigated molecule were computed using DFT calculations. Besides, charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap, molecular electrostatic potential (MEP) were calculated and analyzed. The isotropic chemical shift computed by 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the TBHA calculated using the gauge invariant atomic orbital (GIAO) method also shows good agreement with experimental observations.

Balachandran, V.; Karpagam, V.; Revathi, B.; Kavimani, M.; Santhi, G.

2015-01-01