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1

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

2

Improvement of scale factors for harmonic vibrational frequency calculations using new polarization functions  

NASA Astrophysics Data System (ADS)

Density functional calculations were carried to improve the calculated CO vibrational frequencies for transition metal carbonyls. Two types of density functionals were studied, hybrid and generalized-gradient methods. Using the simplex optimization method, new polarization functions for C and O atoms were obtained. With these new optimized functions, new scaling factors were obtained. The results reveal that, with the new polarization functions, the agreement between the calculated and the experimental values improves considerably. In general, the new scaling factors are very close to unit, with standard uncertainties close to ±0.006 cm-1. The use of the new polarization functions allows more precise calculations of the transition metal carbonyl CO vibrational frequencies.0

Sierraalta, Anibal; Martorell, Guillermo; Ehrmann, Elena; Añez, Rafael

3

Vibrational spectroscopy for glycine adsorbed on silicon clusters: Harmonic and anharmonic calculations for models of the Si(1 0 0)-2 × 1 surface  

NASA Astrophysics Data System (ADS)

The vibrational spectroscopy of a glycine molecule adsorbed on a silicon surface is studied computationally, using different clusters as models for the surface. Harmonic frequencies are computed using density functional theory (DFT) with the B3LYP functional. Anharmonic frequency calculations are carried out using vibrational self-consistent field (VSCF) algorithms on an improved PM3 potential energy surface. The results are compared with experiments on Glycine@Si(1 0 0)-2 × 1. The main findings are: (1) Agreement of the computed frequencies with experiment improves with cluster size. (2) The anharmonic calculations are generally in better agreement with experiment than the harmonic ones. The improvements due to anharmonicity are most significant for hydrogenic stretching. (3) An important part of the anharmonic effects is due to anharmonic coupling between different normal modes of the system. (4) The anharmonic coupling between glycine vibrational modes is much larger than the anharmonic coupling between glycine and "phonon" (cluster) modes. Implications of the results for surface vibrational spectroscopy are discussed.

Shemesh, Dorit; Mullin, Jonathan; Gordon, Mark S.; Gerber, R. Benny

2008-05-01

4

Vibrational spectroscopy of the G...C base pair: experiment, harmonic and anharmonic calculations, and the nature of the anharmonic couplings.  

PubMed

The results of harmonic and anharmonic frequency calculations on a guanine-cytosine complex with an enolic structure (a tautomeric form with cytosine in the enol form and with a hydrogen at the 7-position on guanine) are presented and compared to gas-phase IR-UV double resonance spectral data. Harmonic frequencies were obtained at the RI-MP2/cc-pVDZ, RI-MP2/TZVPP, and semiempirical PM3 levels of electronic structure theory. Anharmonic frequencies were obtained by the CC-VSCF method with improved PM3 potential surfaces; the improved PM3 potential surfaces are obtained from standard PM3 theory by coordinate scaling such that the improved PM3 harmonic frequencies are the same as those computed at the RI-MP2/cc-pVDZ level. Comparison of the data with experimental results indicates that the average absolute percentage deviation for the methods is 2.6% for harmonic RI-MP2/cc-pVDZ (3.0% with the inclusion of a 0.956 scaling factor that compensates for anharmonicity), 2.5% for harmonic RI-MP2/TZVPP (2.9% with a 0.956 anharmonicity factor included), and 2.3% for adapted PM3 CC-VSCF; the empirical scaling factor for the ab initio harmonic calculations improves the stretching frequencies but decreases the accuracy of the other mode frequencies. The agreement with experiment supports the adequacy of the improved PM3 potentials for describing the anharmonic force field of the G...C base pair in the spectroscopically probed region. These results may be useful for the prediction of the pathways of vibrational energy flow upon excitation of this system. The anharmonic calculations indicate that anharmonicity along single mode coordinates can be significant for simple stretching modes. For several other cases, coupling between different vibrational modes provides the main contribution to anharmonicity. Examples of strongly anharmonically coupled modes are the symmetric stretch and group torsion of the hydrogen-bonded NH2 group on guanine, the OH stretch and torsion of the enol group on cytosine, and the NH stretch and NH out-of-plane bend of the non-hydrogen-bonded NH group on guanine. PMID:16834057

Brauer, Brina; Gerber, R Benny; Kabelác, Martin; Hobza, Pavel; Bakker, Joost M; Abo Riziq, Ali G; de Vries, Mattanjah S

2005-08-11

5

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

6

Vibrational spectroscopy of (SO4(2-)).(H2O)n clusters, n=1-5: harmonic and anharmonic calculations and experiment.  

PubMed

The vibrational spectroscopy of (SO4(2-)).(H2O)n is studied by theoretical calculations for n=1-5, and the results are compared with experiments for n=3-5. The calculations use both ab initio MP2 and DFT/B3LYP potential energy surfaces. Both harmonic and anharmonic calculations are reported, the latter with the CC-VSCF method. The main findings are the following: (1) With one exception (H2O bending mode), the anharmonicity of the observed transitions, all in the experimental window of 540-1850 cm(-1), is negligible. The computed anharmonic coupling suggests that intramolecular vibrational redistribution does not play any role for the observed linewidths. (2) Comparison with experiment at the harmonic level of computed fundamental frequencies indicates that MP2 is significantly more accurate than DFT/B3LYP for these systems. (3) Strong anharmonic effects are, however, calculated for numerous transitions of these systems, which are outside the present observation window. These include fundamentals as well as combination modes. (4) Combination modes for the n=1 and n=2 clusters are computed. Several relatively strong combination transitions are predicted. These show strong anharmonic effects. (5) An interesting effect of the zero point energy (ZPE) on structure is found for (SO4(2-)).(H2O)(5): The global minimum of the potential energy corresponds to a C(s) structure, but with incorporation of ZPE the lowest energy structure is C2v, in accordance with experiment. (6) No stable structures were found for (OH-).(HSO4-).(H2O)n, for n

Miller, Yifat; Chaban, Galina M; Zhou, Jia; Asmis, Knut R; Neumark, Daniel M; Gerber, R Benny

2007-09-01

7

Vibrational spectroscopy of (SO42-).(H2O)n clusters, n=1-5: Harmonic and anharmonic calculations and experiment  

NASA Astrophysics Data System (ADS)

The vibrational spectroscopy of (SO42-)•(H2O)n is studied by theoretical calculations for n =1-5, and the results are compared with experiments for n =3-5. The calculations use both ab initio MP2 and DFT/B3LYP potential energy surfaces. Both harmonic and anharmonic calculations are reported, the latter with the CC-VSCF method. The main findings are the following: (1) With one exception (H2O bending mode), the anharmonicity of the observed transitions, all in the experimental window of 540-1850cm-1, is negligible. The computed anharmonic coupling suggests that intramolecular vibrational redistribution does not play any role for the observed linewidths. (2) Comparison with experiment at the harmonic level of computed fundamental frequencies indicates that MP2 is significantly more accurate than DFT/B3LYP for these systems. (3) Strong anharmonic effects are, however, calculated for numerous transitions of these systems, which are outside the present observation window. These include fundamentals as well as combination modes. (4) Combination modes for the n=1 and n =2 clusters are computed. Several relatively strong combination transitions are predicted. These show strong anharmonic effects. (5) An interesting effect of the zero point energy (ZPE) on structure is found for (SO42-)•(H2O)5: The global minimum of the potential energy corresponds to a Cs structure, but with incorporation of ZPE the lowest energy structure is C2v, in accordance with experiment. (6) No stable structures were found for (OH-)•(HSO4-)•(H2O)n, for n ?5.

Miller, Yifat; Chaban, Galina M.; Zhou, Jia; Asmis, Knut R.; Neumark, Daniel M.; Benny Gerber, R.

2007-09-01

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

An investigation into the vibration of harmonic drive systems  

NASA Astrophysics Data System (ADS)

Harmonic drive systems are precise and specific transmission gear systems which are beneficial in terms of the high transmission ratio and almost zero backlash. These inherent and spectacular properties result in using this mechanism in robotic and space sciences where the precision and lightwieght play an important role. This paper presents a vibration analysis of harmonic drive systems using the shell theory. Equations of vibration for the flexspline and the circular spline of the system are derived and used to find the natural frequencies for both parts and, moreover, vibration response of the system under the operating condition is calculated. Also, obtained vibration equations are utilized to study the effects of different involved parameters such as the geometry of the flexspline and its gear tooth, eccentricity, and unbalancing on the vibrational behavior of the system.

Masoumi, M.; Alimohammadi, H.

2013-12-01

10

Tiltrotor Vibration Reduction Through Higher Harmonic Control  

Microsoft Academic Search

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

Mark W. Nixon; T. Ben Settle

1997-01-01

11

HIGHER HARMONIC CONTROL FOR TILTROTOR VIBRATION REDUCTION  

Microsoft Academic Search

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

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

12

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

13

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

14

Driving an Active Vibration Balancer to Minimize Vibrations at the Fundamental and Harmonic Frequencies  

NASA Technical Reports Server (NTRS)

Vibrations of a principal machine are reduced at the fundamental and harmonic frequencies by driving the drive motor of an active balancer with balancing signals at the fundamental and selected harmonics. Vibrations are sensed to provide a signal representing the mechanical vibrations. A balancing signal generator for the fundamental and for each selected harmonic processes the sensed vibration signal with adaptive filter algorithms of adaptive filters for each frequency to generate a balancing signal for each frequency. Reference inputs for each frequency are applied to the adaptive filter algorithms of each balancing signal generator at the frequency assigned to the generator. The harmonic balancing signals for all of the frequencies are summed and applied to drive the drive motor. The harmonic balancing signals drive the drive motor with a drive voltage component in opposition to the vibration at each frequency.

Holliday, Ezekiel S. (Inventor)

2014-01-01

15

Vibrational calculations for the H 2O … CO complex  

NASA Astrophysics Data System (ADS)

The H 2O-CO complex was studied with DFT calculations. The complex has two stable structures, H 2O-CO and H 2O-OC, and their BSSE-corrected interaction energies at the CR-CC(2,3)/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ level of theory are -8.43 and -3.38 kJ mol -1. The vibrational properties of the complexes were studied via harmonic and anharmonic calculations. The harmonic calculations are able to give a qualitative view on the complexes whereas the anharmonic CC-VSCF calculations are able to place the vibrational transitions close to their experimentally determined positions. The anharmonic calculations also indicate that both complex structures have a rich overtone and combination spectra.

Lundell, Jan; Latajka, Zdzis?aw

2008-09-01

16

Fundamental vibrational frequencies of small polyatomic molecules from density-functional calculations and vibrational perturbation theory  

NASA Astrophysics Data System (ADS)

An extensive study of fundamental frequencies and anharmonic vibrational constants for polyatomic molecules obtained from Becke three parameter Lee-Yang-Parr (B3LYP) and Becke-Perdew (BP86) density functional calculations is presented. These calculations are based on standard perturbation theory, and are compared to correlation-corrected vibrational self-consistent field (CC-VSCF) calculations for the water dimer. The anharmonic corrections obtained from density-functional calculations compare well with experimental values and with results from correlated ab initio methods. While fundamental frequencies from B3LYP calculations are reliable, they are considerably too small for BP86 calculations. Consequently, the good agreement of unscaled harmonic frequencies from BP86 calculations with experimental frequencies is due to an error cancellation effect. This is of importance for the prediction of vibrational spectra for large molecules, because the perturbation theory approach naturally becomes unreliable for very large molecules due to the increasing number of anharmonic resonance effects. These resonances seriously limit the applicability of perturbation theoretical approaches to anharmonic vibrational constants, whereas the computational effort for the calculation of cubic and quartic force constants, is feasible because calculations can be performed very efficiently by a parallelized calculation of harmonic force constants for several structures, which are distorted along the normal coordinates, followed by numerical differentiation.

Neugebauer, Johannes; Hess, Bernd A.

2003-04-01

17

Calculation of Maximum Harmonic Currents and Voltages on Transmission Lines  

Microsoft Academic Search

This paper presents a method for calculating the location and magnitude of the maximum harmonic currents and voltages on a transmission line, given calculated or measured terminal values. This information is normally unavailable. However, as the number of harmonic sources on the system increases, the location and magnitude of these harmonic maximums will be of increasing importance.

R. D. Shultz; R. A. Smith; G. L. Hickey

1983-01-01

18

Balancing Vibrations at Harmonic Frequencies by Injecting Harmonic Balancing Signals into the Armature of a Linear Motor/Alternator Coupled to a Stirling Machine  

NASA Technical Reports Server (NTRS)

Vibrations at harmonic frequencies are reduced by injecting harmonic balancing signals into the armature of a linear motor/alternator coupled to a Stirling machine. The vibrations are sensed to provide a signal representing the mechanical vibrations. A harmonic balancing signal is generated for selected harmonics of the operating frequency by processing the sensed vibration signal with adaptive filter algorithms of adaptive filters for each harmonic. Reference inputs for each harmonic are applied to the adaptive filter algorithms at the frequency of the selected harmonic. The harmonic balancing signals for all of the harmonics are summed with a principal control signal. The harmonic balancing signals modify the principal electrical drive voltage and drive the motor/alternator with a drive voltage component in opposition to the vibration at each harmonic.

Holliday, Ezekiel S. (Inventor)

2014-01-01

19

Vibrational structure theory: new vibrational wave function methods for calculation of anharmonic vibrational energies and vibrational contributions to molecular properties.  

PubMed

A number of recently developed theoretical methods for the calculation of vibrational energies and wave functions are reviewed. Methods for constructing the appropriate quantum mechanical Hamilton operator are briefly described before reviewing a particular branch of theoretical methods for solving the nuclear Schrödinger equation. The main focus is on wave function methods using the vibrational self-consistent field (VSCF) as starting point, and includes vibrational configuration interaction (VCI), vibrational Møller-Plesset (VMP) theory, and vibrational coupled cluster (VCC) theory. The convergence of the different methods towards the full vibrational configuration interaction (FVCI) result is discussed. Finally, newly developed vibrational response methods for calculation of vibrational contributions to properties, energies, and transition probabilities are discussed. PMID:17551617

Christiansen, Ove

2007-06-21

20

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

21

Optimized coordinates in vibrational coupled cluster calculations  

NASA Astrophysics Data System (ADS)

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; Yagi, Kiyoshi; Christiansen, Ove

2014-04-01

22

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

Microsoft Academic Search

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

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

2010-01-01

23

Acoustic method for calibration of audiometric bone vibrators. II. Harmonic distortion  

PubMed Central

A previous report [Margolis and Stiepan (2012). “Acoustic method for calibration of audiometric bone vibrators,” J. Acoust. Soc. Am. 131, 1221–1225] described a reliable, inexpensive, acoustic method for calibration of audiometric bone vibrators. As a follow up to that report harmonic distortion measurements were made with the standard electromechanical method and the acoustic method using five Radioear B71 vibrators and one Radioear B81 prototype vibrator. Lower distortion was seen for measurements made with the acoustic method compared to the electromechanical method and for the Radioear B81 vibrator compared to the Radioear B71 vibrator. PMID:23862903

Ginter, Samantha M.; Margolis, Robert H.

2013-01-01

24

Acoustic method for calibration of audiometric bone vibrators. II. Harmonic distortion.  

PubMed

A previous report [Margolis and Stiepan (2012). "Acoustic method for calibration of audiometric bone vibrators," J. Acoust. Soc. Am. 131, 1221-1225] described a reliable, inexpensive, acoustic method for calibration of audiometric bone vibrators. As a follow up to that report harmonic distortion measurements were made with the standard electromechanical method and the acoustic method using five Radioear B71 vibrators and one Radioear B81 prototype vibrator. Lower distortion was seen for measurements made with the acoustic method compared to the electromechanical method and for the Radioear B81 vibrator compared to the Radioear B71 vibrator. PMID:23862903

Ginter, Samantha M; Margolis, Robert H

2013-07-01

25

Nonlinear response of a harmonic diatomic molecule: Algebraic nonperturbative calculation  

SciTech Connect

Even harmonic molecules display a nonlinear behavior when driven by an inhomogeneous field. We calculate the response of single harmonic molecules to a monochromatic time and space dependent electric field E(r,t) of frequency {omega} employing exact algebraic methods. We evaluate the responses at the fundamental frequency {omega} and at successive harmonics 2{omega}, 3{omega}, etc., as a function of the intensity and of the frequency of the field and compare the results with those of first and second order perturbation theory.

Recamier, Jose; Mochan, W. Luis; Maytorena, Jesus A. [Centro de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico, Apartado Postal 48-3, Cuernavaca, Morelos, 62251 (Mexico)

2005-08-15

26

Ab initio calculation of harmonic force fields and vibrational spectra for the arsine oxides and sulfides R sub 3 AsY (R = H, F; Y = O, S) and related compounds  

SciTech Connect

Ab initio self-consistent-field calculations using effective core potentials and polarized double-zeta basis sets are reported for the arsenic compounds H{sub 3}As, H{sub 3}AsO, H{sub 3}AsS, F{sub 3}As, F{sub 3}AsO, F{sub 3}AsS, cis- and trans-H{sub 2}AsOH, and HAsO. The calculated geometries, rotational constants, vibrational frequencies, Coriolis coupling constants, centrifugal distortion constants, infrared band intensities, and force fields are compared with the available experimental data. Good agreement is found in the case of the known molecules, especially H{sub 3}As and F{sub 3}As, so that the predictions for the unknown molecules are expected to be realistic. The theoretical results confirm a recent spectroscopic identification of H{sub 3}AsO, H{sub 2}AsOH, and HAsO and suggest reassignment of several observed frequencies.

Schneider, W.; Thiel, W. (Bergische Universitaet-Gesamthochschule, Wuppertal (West Germany)); Komornicki, A. (Polyatomics Research Institute, Mountain View, CA (USA))

1990-04-05

27

Calculation of four-particle harmonic-oscillator transformation brackets  

NASA Astrophysics Data System (ADS)

A procedure for precise calculation of the three- and four-particle harmonic-oscillator (HO) transformation brackets is presented. The analytical expressions of the four-particle HO transformation brackets are given. The computer code for the calculations of HO transformation brackets proves to be quick, efficient and produces results with small numerical uncertainties. Program summaryProgram title: HOTB Catalogue identifier: AEFQ_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFQ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 1247 No. of bytes in distributed program, including test data, etc.: 6659 Distribution format: tar.gz Programming language: FORTRAN 90 Computer: Any computer with FORTRAN 90 compiler Operating system: Windows, Linux, FreeBSD, True64 Unix RAM: 8 MB Classification: 17.17 Nature of problem: Calculation of the three-particle and four-particle harmonic-oscillator transformation brackets. Solution method: The method is based on compact expressions of the three-particle harmonics oscillator brackets, presented in [1] and expressions of the four-particle harmonics oscillator brackets, presented in this paper. Restrictions: The three- and four-particle harmonic-oscillator transformation brackets up to the e=28. Unusual features: Possibility of calculating the four-particle harmonic-oscillator transformation brackets. Running time: Less than one second for the single harmonic-oscillator transformation bracket. References:G.P. Kamuntavi?ius, R.K. Kalinauskas, B.R. Barret, S. Mickevi?ius, D. Germanas, Nuclear Physics A 695 (2001) 191.

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

2010-02-01

28

Coupled rotor-flexible fuselage vibration reduction using open loop higher harmonic control  

NASA Technical Reports Server (NTRS)

A fundamental study of vibration prediction and vibration reduction in helicopters using active controls was performed. The nonlinear equations of motion for a coupled rotor/flexible fuselage system have been derived using computer algebra on a special purpose symbolic computer facility. The trim state and vibratory response of the helicopter are obtained in a single pass by applying the harmonic balance technique and simultaneously satisfying the trim and the vibratory response of the helicopter for all rotor and fuselage degrees of freedom. The influence of the fuselage flexibility on the vibratory response is studied. It is shown that the conventional single frequency higher harmonic control is capable of reducing either the hub loads or only the fuselage vibrations but not both simultaneously. It is demonstrated that for simultaneous reduction of hub shears and fuselae vibrations a new scheme called multiple higher harmonic control is required.

Papavassiliou, I.; Friedmann, P. P.; Venkatesan, C.

1991-01-01

29

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

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

Beyond vibrational self-consistent-field methods: Benchmark calculations for the fundamental vibrations of ethylene  

NASA Astrophysics Data System (ADS)

A number of different methods for calculation of vibrational energies are reviewed and tested for calculation of the fundamental vibrational frequencies for ethylene. The methods tested for the description of the vibrational states are vibrational self-consistent field (VSCF), vibrational configuration interaction (VCI), vibrational Møller-Plesset theory (VMP), and vibrational coupled cluster (VCC). The convergence of the different methods toward the full vibrational configuration interaction (FVCI) result is discussed for a modest-sized one-mode basis. For larger one-mode basis sets results are presented for selected methods. Different representations of the potential energy surface are compared including full and partial quartic force field as well as expansions using up to sixth derivatives of the potential energy surface. Using MP2 electronic structure theory, the electronic structure basis set convergence is tested.

Christiansen, Ove; Luis, Josep M.

32

Calculation of the background emitted during high-harmonic generation  

SciTech Connect

We present a method for calculating the spectrum emitted by an atom in an intense laser field. This method is based on the direct use of the acceleration of the atomic electron rather than the dipole moment of the atom. We show, using a numerical calculation in one dimension, that this method produces a more exact numerical evaluation of the spectrum. This technique is particularly important in determining the background to the high harmonics emitted by the atom.

Burnett, K.; Reed, V.C. (Clarendon Laboratory, Parks Road, Oxford OX13PU (United Kingdom)); Cooper, J. (Joint Institute for Laboratory Astrophysics, University of Colorado National Institute of Standards and Technology, Boulder, Colorado 80309-0440 (United States)); Knight, P.L. (The Blackett Laboratory, Imperial College, London SW72BZ (United Kingdom))

1992-03-01

33

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

34

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

35

Vibrational Circular Dichroism Intensities: Ab Initio Calculations  

Microsoft Academic Search

\\u000a Of the various chiroptical techniques, one of the newest, vibrational circular dichroism (VCD) promises to yield the greatest\\u000a amount of structural and stereochemical information. Since the earliest theoretical models [1] and the first successful experimental measurements [2,3], VCD has seen rapid advances in instrumentation and theory. Reliable measurements over most of the vibrational spectrum\\u000a can be carried out, and reliable

Arvi Rauk

36

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

37

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

38

Direct calculation of anharmonic vibrational states of polyatomic molecules using potential energy surfaces calculated from density functional theory  

NASA Astrophysics Data System (ADS)

Potential energy surface points computed from variants of density functional theory (DFT) are used to calculate directly the anharmonic vibrational frequencies of H2O, Cl-H2O, and (H2O)2. The method is an adaptation to DFT of a recent algorithm for direct calculations of anharmonic vibrational frequencies using ab initio electronic structure codes. The DFT calculations are performed using the BLYP and the B3LYP functionals and the results are compared with experiment, and also with those calculated directly from a potential energy surface obtained using ab initio Möller-Plesset second-order perturbation theory (MP2). The direct calculation of the vibrational states from the potential energy points is performed using the correlation-corrected vibrational self-consistent field (CC-VSCF) method. This method includes anharmonicity and correlations between different vibrational modes. The accuracy of this method is examined and it is shown that for the experimentally measured transitions the errors in the CC-VSCF calculations are much less than the errors due to the potential energy surface. By comparison with the experimentally measured frequencies the CC-VSCF method thus provides a test for the quality of the potential energy surfaces. The results obtained with the B3LYP functional, in contrast to those of the BLYP functional, are of comparable quality to those obtained with MP2. The B3LYP anharmonic frequencies are in good agreement with experiment, showing this DFT method describes well the anharmonic part of the potential energy surface. The BLYP results systematically underestimate both the harmonic and anharmonic frequencies and indicate that using this functional for the description of hydrogen-bonded systems may cause significant errors.

Wright, Nicholas J.; Gerber, R. Benny

2000-02-01

39

HELICOPTER VIBRATORY LOADS AND VIBRATIONS REDUCTION USING HIGHER-HARMONIC CONTROL  

E-print Network

) in rotorcraft terminol- ogy) [9]. The main idea behind HHC is to smooth the rotor aerodynamics. A rotor with a number of N equally spaced identical blades acts as a fil- ter when all the blade root loads are summedHELICOPTER VIBRATORY LOADS AND VIBRATIONS REDUCTION USING HIGHER-HARMONIC CONTROL Aykut Tamer

Yaman, Yavuz

40

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

41

Calculation of Vibrational Spectra of p-Ethylbenzenesulfonic Acid Hydrates  

NASA Astrophysics Data System (ADS)

Quantum-chemical calculations of vibrational spectra of the sulfonated ion-exchanger model p-ethylbenzenesulfonic acid hydrated by 1-10 water molecules and its dimer were calculated by the non-empirical SCF MO LCAO method with the 6-31G(d) basis set. The calculated results were compared with experimental IR and Raman spectra of sulfonated ion exchangers. The infl uence of hydration on the vibrational frequencies of functional groups in the ion exchangers was analyzed. It was shown that the sulfonic acid was completely dissociated if three and more water molecules per functional group were present. Bands near 1130 cm-1 were due to S-O-H bending vibrations in the absence of water molecules and C-S-O-H3O combination vibrations with 3-6 water molecules per sulfonic acid.

Zelenkovskii, V. M.; Bezyazychnaya, T. V.; Soldatov, V. S.

2013-09-01

42

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

43

Anharmonic vibrational spectroscopy calculations for proton-bound amino acid dimers.  

PubMed

Results of anharmonic frequency calculations carried out for GlysLysH(+) and GlyGlyH(+) are presented and compared to gas phase electrospray ionization (ESI) spectroscopy experiments. Anharmonic frequencies are obtained via correlation-corrected vibrational self-consistent field (CC-VSCF) calculations. The potential used is based on the PM3 semiempirical electronic structure method, but improved by fitting to ab initio MP2 calculations at the harmonic level. The key results are as follows: (1) Hydrogens acting as intermolecular bridges have very anharmonic stretches whose frequencies cannot be reliably predicted by the harmonic approximation. An example is the carboxylate bound NH(3)(+) stretch. (2) The computed anharmonic vibrational frequencies are in good agreement with experiment and provides a very large improvement over harmonic frequencies especially for OH and NH stretches. For example the calculated CC-VSCF frequencies of GlysLysH(+) and GlyGlyH(+) have overall average deviations of 1.35% and 1.48% only, respectively, from experiment. (3) The harmonic OH bond stretching frequency deviates by 6.64% from experiments. The CC-VSCF calculations reduce this deviation by more than an order of magnitude to 0.56%. The anharmonicity of the OH stretch is intrinsic, rather than due to coupling with other modes. (4) Anharmonic coupling between the NH(3)(+) stretch and several other normal modes is strong, and provide the main contribution for the anharmonicity of this mode. Properties of the potential energy surfaces of the proton-bound complexes are briefly discussed in light of the results. PMID:19061325

Adesokan, Adeyemi A; Gerber, R B

2009-03-12

44

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

PubMed Central

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

45

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

46

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

47

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

48

An active control system for helicopter vibration reduction by higher harmonic pitch  

NASA Technical Reports Server (NTRS)

An analytical study defining the basic configuration of an active control system to reduce helicopter vibrations is presented. Theoretical results for a nonlinear four-bladed single rotor helicopter simulation are discussed, showing that vibration reductions on the order of 80-90% for airspeeds up to 150 kn can be expected when using a higher harmonic pitch in an active feedback control system. The rotor performance penalty associated with this level of vibration reduction is about 1-3% and the increase in rotor blade stresses is considered to be low. The location of sensor accelerometers proved to be significant for vibration reductions, and it is noted that the RTSA controller is tolerant of sensor signal noise.

Taylor, R. B.; Farrar, F. A.; Miao, W.

1980-01-01

49

Harmonic two-phonon {gamma}-vibrational state in neutron-rich {sup 106}Mo  

SciTech Connect

The neutron-rich {sup 106}Mo nucleus has been studied by prompt {gamma}-ray spectroscopy following the spontaneous fission of {sup 248}Cm. The characteristics of the rotational band built on a state at 1435 keV identifies the band head as the best candidate for a harmonic double-phonon {ital K}{sup {pi}}=4{sup +} {gamma}-vibrational state observed so far.

Guessous, A.; Schulz, N.; Phillips, W.R.; Ahmad, I.; Bentaleb, M.; Durell, J.L.; Jones, M.A.; Leddy, M.; Lubkiewicz, E.; Morss, L.R.; Piepenbring, R.; Smith, A.G.; Urban, W.; Varley, B.J. [Centre de Recherches Nucleaires, IN2P3-CNRS/Universite Louis Pasteur, 67037 Strasbourg (France)] [Centre de Recherches Nucleaires, IN2P3-CNRS/Universite Louis Pasteur, 67037 Strasbourg (France); [Department of Physics, University of Manchester, M13 9PL (United Kingdom); [Argonne National Laboratory, Argonne, Illinois 60439 (United States); [Institut des Sciences Nucleaires, IN2P3-CNRS/UJF, 38026 Grenoble (France)

1995-09-18

50

Calculation of unsteady linearized Euler flows in cascades using harmonically deforming grids  

NASA Technical Reports Server (NTRS)

A method for calculating unsteady, inviscid, compressible flows in cascades is presented. Using the linearized Euler technique, the flow is decomposed into a steady or mean flow plus a harmonically varying small disturbance flow. The equations that describe the small disturbance flow are linear variable coefficient equations, and are solved using a pseudo-time time marching Lax-Wendroff technique. Unlike previous linearized methods, however, the solution is computed on a harmonically deforming computational grid that conforms to the motion of the vibrating airfoils. The mean flow and perturbation flow solutions are defined in the deforming coordinate system rather than in a coordinate system fixed in space. Hence, no extrapolation terms are required to implement the upwash boundary conditions at the airfoil surfaces, significantly improving the accuracy of the method. For transonic flow calculations, unsteady shock motions are modelled using shock capturing. The unsteady loads due to the shock motion are then seen as pressure impulses. Representative computational results are presented for transonic channel flows and subsonic and transonic cascade flows.

Hall, Kenneth C.; Clark, William S.

1991-01-01

51

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

SciTech Connect

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, E-mail: j.neugebauer@uni-muenster.de [Theoretische Organische Chemie, Organisch-Chemisches Institut and Center for Multiscale Theory and Computation, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149 Münster (Germany)

2014-10-28

52

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

53

Diabatic Versus Adiabatic Calculation of Torsion-Vibration Interactions  

NASA Astrophysics Data System (ADS)

The introductory part of this talk will deal briefly with two historical topics: (i) use of the words adiabatic, nonadiabatic, and diabatic in thermodynamics and quantum mechanics, and (ii) application of diabatic and adiabatic ideas to vibrational energy level calculations for a pair of diatomic-molecule potential energy curves exhibiting an avoided crossing. The main part of the talk will be devoted to recent work with Li-Hong Xu and Ron Lees on how ab initio projected frequency calculations for small-amplitude vibrations along the large-amplitude internal rotation path in methanol can best be used to help guide experimental assignments and fits in the IR vibrational spectrum. The three CH stretching vibrations for CH_{3}OH can conveniently be represented as coefficients multiplying three different types of basis vibrations, i.e., as coefficients of: (i) the local mode C-H_i bond displacements ?r_{i} for hydrogens H_{1}, H_{2} and H_{3} of the methyl top, (ii) symmetrized linear combinations of the three ?r_{i} of species A_{1} oplus E in the permutation-inversion group G_{6} = C_{3v} appropriate for methanol, or (iii) symmetrized linear combinations of the three ?r_{i} of species 2A_{1} oplus A_{2} in the permutation-inversion group G_{6}. In this talk, we will focus on diabatic and adiabatic computations for the A_{1} oplus E basis vibrations of case (ii) above. We will briefly explain how Jahn-Teller-like and Renner-Teller-like torsion-vibration interaction terms occurring in the potential energy expression in the diabatic calculation become torsion-vibration Coriolis interaction terms occurring in the kinetic energy expression of the adiabatic calculations, and also show how, for algebraically solvable parameter choices, the same energy levels are obtained from either calculation. A final conclusion as to which approach is computationally superior for the numerical data given in a quantum chemistry output file has not yet been arrived at.

Hougen, Jon T.

2013-06-01

54

Influence of the solvent representation on vibrational entropy calculations: generalized born versus distance-dependent dielectric model.  

PubMed

The harmonic model is the most popular approximation for estimating the "configurational" entropy of a solute in molecular mechanics/Poisson-Boltzmann solvent accessible surface area (MM/PBSA)-type binding free energy calculations. Here, we investigate the influence of the solvent representation in the harmonic model by comparing estimates of changes in the vibrational entropies for 30 trypsin/ligand complexes on ligand binding. Second derivatives of Amber generalized Born (GB) solvation models are available in the nucleic acid builder code. They allow one to use these models for the calculation of vibrational entropies instead of using a simpler solvation model based on a distance-dependent dielectric (DDD) constant. Estimates of changes in the vibrational entropies obtained with a DDD model are systematically and significantly larger, by on average, 6 kcal mol(-1) (at T = 300 K), than estimates obtained with a GB model and so are more favorable for complex formation. The difference becomes larger the more the vibrational entropy contribution disfavors complex formation, that is, the larger the ligand is (for the complexes considered here). A structural decomposition of the estimates into per-residue contributions reveals polar interactions between the ligand and the surrounding protein, in particular involving charged nitrogens, as a main source of the differences. Snapshots minimized with the DDD model showed a structural deviation from snapshots minimized in explicit water that is larger by, on average, 0.5 Å RMSD compared to snapshots that were minimized with GB(HCT) . As experimental vibrational entropies of biomacromolecules are elusive, there is no direct way to establish a solvent model's superiority. Thus, we can only recommend using the GB harmonic model for vibrational entropy calculations based on the reasoning that smaller structural deviations should point to the implicit solvent model that closer approximates the energy landscape of the solute in explicit solvent. PMID:22298332

Kopitz, Hannes; Cashman, Daniel A; Pfeiffer-Marek, Stefania; Gohlke, Holger

2012-04-01

55

Nonlinear coupled rotor-fuselage helicopter vibration studies with higher harmonic control  

NASA Technical Reports Server (NTRS)

This paper addresses the problem of vibration prediction and vibration reduction in helicopters by means of active control methodologies. The nonlinear equations of a coupled rotor/flexible-fuselage system have been derived using computer algebra, thus relegating this tedious task to the computer. In the solution procedure the trim state and vibratory response of the helicopter are obtained in a single pass by using a harmonic balance technique and simultaneously satisfying the trim and the vibratory response of the helicopter in all the rotor and fuselage degrees of freedom. Using this solution procedure, the influence of the fuselage flexibility on the vibratory response is studied. In addition, it is shown that the conventional single frequency HHC is capable of reducing either the hub loads or only the fuselage vibrations but not both simultaneously. A new scheme called MHHC, having multiple higher harmonic pitch inputs, was used to accomplish this task of simultaneously reducing both the vibratory hub loads and fuselage vibratory response. In addition, the uniqueness of this MHHC scheme is explained in detail.

Friedmann, P. P.; Venkatesan, C.; Papavassiliou, I.

1990-01-01

56

Molecular structure and vibrational spectra of ibuprofen using density function theory calculations  

NASA Astrophysics Data System (ADS)

The molecular geometry and the theoretical harmonic frequencies and infrared intensities of ibuprofen were calculated for all the molecules using five different density functional methods (mPW1PW91, B3PW91, B3LYP, HCTH and LSDA) with five basic sets, including 6-311G, 6-311++G, 6-311+G (d, p), 6-311++G (d, p) and 6-311++G (2d, 2p). The purpose of this research was to compare the performance of different DFT methods at different basis sets in predicting geometry and vibration spectrum of ibuprofen. The optimized geometric band lengths and bond angles obtained by using mPW1PW91 at 6-311++G (d, p) and 6-311++G (2d, 2p) basic sets show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of ibuprofen with calculated results indicates that the B3PW91/6-311++G (2d, 2p) level is superior to all the remaining levels for predicting all the vibration spectra on average for ibuprofen.

Liu, Lekun; Gao, Hongwei

2012-04-01

57

A piezoelectric pulse generator for low frequency non-harmonic vibration  

NASA Astrophysics Data System (ADS)

This paper reports a new piezoelectric prototype for pulse generation by energy harvesting from low frequency non-harmonic vibration. The pulse generator presented here consists of two parts: the electromechanical part and the load circuit. A metal rolling rod is used as the proof mass, moving along the substrate to achieve both actuating of the piezoelectric cantilever by magnetic coupling and self-synchronous switching of the circuit. By using this new approach, the energy from the piezoelectric transduction mechanism is regulated simultaneously when it is extracted. This allows a series of tuneable pulses to be generated, which can be applied to self-powered RF wireless sensor network (WSN) nodes.

Jiang, Hao; Yeatman, Eric M.

2013-12-01

58

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

59

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

60

Calculation of PETN molecular crystal vibrational frequencies under hydrostatic pressure  

NASA Astrophysics Data System (ADS)

First-principles calculations of the effects of hydrostatic pressure on pentaerythritol tetranitrate (PETN) are performed using the all-electron CRYSTAL03 program. The procedure for applying hydrostatic pressure by performing a series of volumetric changes coincident with lattice constant and internal coordinate optimization using various scripts and support programs is described. Once the optimized internal coordinates and lattice constants have been obtained for a given hydrostatic pressure, a separate algorithm consisting of additional scripts and programs is employed for performing a complete normal-mode analysis, with analytic first derivatives and numeric second derivatives of the total energy. The eigenvalues obtained provide the vibrational frequencies and the eigenvectors are used for mode identification. The role of the Gaussian basis sets chosen and the exchange-correlation potential used is discussed. The vibrational frequencies obtained at ambient pressure are shown to compare well with experiment and gas-phase calculations. The shift of the vibrational frequencies under hydrostatic pressure is compared with experiment.

Perger, Warren; Zhao, Jijun

2005-03-01

61

Calculation of the vibrational spectra of betaine hydrochloride  

NASA Astrophysics Data System (ADS)

The molecular geometries of betaine hydrochloride, BET·HCl, and free protonated betaine, BET·H +, were calculated with the 6-31G(d,p) basis set at the SCF, MP2 and DFT levels of theory. At the SCF level, the minimum energy corresponds to the ionic pair, B +Htctdot;A -, however, the equilibrium Otctdot;Cl distance is 0.14 Å shorter than the X-ray value. Inclusion of the correlation effects, both at the MP2 and DFT levels, predicts a minimum energy for the molecular complex, Btctdot;H-A, with the equilibrium Otctdot;Cl distance close to the experimental value. The frequencies and intensities of the vibrational bands of BET·HCl, BET·DCl and BET·H + were calculated at the SCF and DFT levels and compared with the solid IR spectra. All measured IR bands were interpreted in term of the calculated vibrational modes. The rms deviations between the experimental and calculated SCF frequencies were 21 and 29 cm -1 for BET·HCl and BET·DCl, respectively. The computed band intensities agree qualitatively with the experimental data. The coupling of the CO stretching and OH bending modes are discussed. The summation bands are probably enhanced in intensity by Fermi resonance with the fundamentals responsible for the main ?(OH) (?(OD) absorption region.

Szafran, Miroslaw; Koput, Jacek

1997-02-01

62

Super and sub-harmonic response calculations for a torsional system with clearance nonlinearity using the harmonic balance method  

Microsoft Academic Search

This article presents a new multi-term harmonic balance method (HBM) for nonlinear frequency response calculations of a torsional sub-system containing a clearance type nonlinearity. The ability of the simplified subsystem to capture the salient behavior of the larger system is verified by the comparison of results to experimental data. Unlike previous analytical and numerical methods, the proposed HBM includes adaptive

T. C. Kim; T. E. Rook; R. Singh

2005-01-01

63

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

64

GROUND VIBRATION GENERATED BY A HARMONIC LOAD ACTING ON A RAILWAY TRACK  

Microsoft Academic Search

A calculation method has been produced for the propagation of vibration in the ground from a stationary oscillating load applied via a railway track structure. The model includes the track as an infinite layered beam structure resting on a ground made up of infinite parallel homogeneous elastic layers. These layers may either be constrained at the lower interface or coupled

X. Sheng; C. J. C. Jones; M. Petyt

1999-01-01

65

A new vibrational study of Acetazolamide compound based on normal coordinate analysis and DFT calculations  

NASA Astrophysics Data System (ADS)

We have studied the 5-acetamido-1,3,4-thiadiazole-2-sulphonamide compound and characterized it by infrared and Raman spectroscopy in the solid phase. The Density Functional Theory (DFT) method together with Pople's basis set show that two stable molecules for the compound have been theoretically determined in the gas phase, and that only the more stable conformation is present in the solid phase, as was experimentally observed. The harmonic vibrational wavenumbers for the optimized geometry were calculated at B3LYP/6-31G ? and B3LYP/6-311++G ?? levels at the proximity of the isolated molecule. For a complete assignment of the vibrational spectra in the compound solid, DFT calculations were combined with Pulaýs Scaled Quantum Mechanics Force Field (SQMFF) methodology in order to fit the theoretical wavenumber values to the experimental ones. In this way, a complete assignment of all of the observed bands in the infrared spectrum for the compound was performed. The natural bond orbital (NBO) study reveals the characteristics of the electronic delocalization of the two structures, while the corresponding topological properties of electronic charge density are analysed by employing Bader's Atoms in the Molecules theory (AIM).

Brandán, S. A.; Ero?lu, E.; Ledesma, A. E.; Oltulu, O.; Yalç?nkaya, O. B.

2011-05-01

66

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

NASA Astrophysics Data System (ADS)

Quadratic response functions are derived and implemented for a vibrational configuration interaction state. Combined electronic and vibrational quadratic response functions are derived using Born-Oppenheimer vibronic product wave functions. Computational tractable expressions are derived for determining the total quadratic response contribution as a sum of contributions involving both electronic and vibrational linear and quadratic response functions. In the general frequency-dependent case this includes a new and more troublesome type of electronic linear response function. Pilot calculations for the FH, H2O, CH2O, and pyrrole molecules demonstrate the importance of vibrational contributions for accurate comparison to experiment and that the vibrational contributions in some cases can be very large. The calculation of transition properties between vibrational states is combined with sum-over-states expressions for analysis purposes. On the basis of this some simple analysis methods are suggested. Also, a preliminary study of the effect of finite lifetimes on quadratic response functions is presented.

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

2009-10-01

67

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

68

A study of coupled rotor-fuselage vibration with higher harmonic control using a symbolic computing facility  

NASA Technical Reports Server (NTRS)

A fundamental study of vibration prediction and vibration reduction in helicopters using active controls was performed. The nonlinear equations of motion for a coupled rotor/flexible fuselage system have been derived using computer algebra on a special purpose symbolic computing facility. The details of the derivation using the MACSYMA program are described. The trim state and vibratory response of the helicopter are obtained in a single pass by applying the harmonic balance technique and simultaneously satisfying the trim and the vibratory response of the helicopter for all rotor and fuselage degrees of freedom. The influence of the fuselage flexibility on the vibratory response is studied. It is shown that the conventional single frequency higher harmonic control (HHC) capable of reducing either the hub loads or only the fuselage vibrations but not both simultaneously. It is demonstrated that for simultaneous reduction of hub shears and fuselage vibrations a new scheme called multiple higher harmonic control (MHHC) is required. The fundamental aspects of this scheme and its uniqueness are described in detail, providing new insight on vibration reduction in helicopters using HHC.

Papavassiliou, I.; Venkatesan, C.; Friedmann, P. P.

1990-01-01

69

Vibrational spectra of ?-glucose, ?-glucose, and sucrose: anharmonic calculations and experiment.  

PubMed

The anharmonic vibrational spectra of ?-D-glucose, ?-D-glucose, and sucrose are computed by the vibrational self-consistent field (VSCF) method, using potential energy surfaces from electronic structure theory, for the lowest energy conformers that correspond to the gas phase and to the crystalline phase, respectively. The results are compared with ultraviolet-infrared (UV-IR) spectra of phenyl ?-D-glucopyranoside in a molecular beam, with literature results for sugars in matrices and with new experimental data for the crystalline state. Car-Parrinello dynamics simulations are also used to study temperature effects on the spectra of ?-D-glucose and ?-D-glucose and to predict their vibrational spectra at 50, 150, and 300 K. The effects of temperature on the spectral features are analyzed and compared with results of the VSCF calculations conducted at 0 K. The main results include: (i) new potential surfaces, constructed from Hartree-Fock, adjusted to fit harmonic frequencies from Møller-Plesset (MP2) calculations, that give very good agreement with gas phase, matrix, and solid state spectra; (ii) computed infrared spectra of the crystalline solid of ?-glucose, which are substantially improved by including mimic groups that represent the effect of the solid environment on the sugar; and (iii) identification of a small number of combination-mode transitions, which are predicted to be strong enough for experimental observation. The results are used to assess the role of anharmonic effects in the spectra of the sugars in isolation and in the solid state and to discuss the spectroscopic accuracy of potentials from different electronic structure methods. PMID:21391638

Brauer, Brina; Pincu, Madeleine; Buch, Victoria; Bar, Ilana; Simons, John P; Gerber, R Benny

2011-06-16

70

An improved filtered spherical harmonic method for transport calculations  

SciTech Connect

Motivated by the work of R. G. McClarren, C. D. Hauck, and R. B. Lowrie on a filtered spherical harmonic method, we present a new filter for such numerical approximations to the multi-dimensional transport equation. In several test problems, we demonstrate that the new filter produces results with significantly less Gibbs phenomena than the filter used by McClarren, Hauck and Lowrie. This reduction in Gibbs phenomena translates into propagation speeds that more closely match the correct propagation speed and solutions that have fewer regions where the scalar flux is negative. (authors)

Ahrens, C. [Department of Applied Mathematics and Statistics, Colorado School of Mines, Golden, CO 80401 (United States); Merton, S. [Computational Physics Group, AWE Aldermaston, Berkshire (United Kingdom)

2013-07-01

71

Crystal and molecular structure, conformational, vibrational properties and DFT calculations of melaminium bis (hydrogen oxalate)  

NASA Astrophysics Data System (ADS)

Single crystals of melaminium bis (hydrogen oxalate) (MOX) were grown by slow evaporation method. X-ray powder diffraction analysis indicates that MOX crystallizes in monoclinic system (space group C2/c) and the calculated lattice constants are a = 20.075 ± 0.123 ?, b = 8.477 ± 0.045 ?, c = 6.983 ± 0.015, ? = ? 90° and ? = 102.6 ± 0.33°. Thermal analysis confirms that MOX is thermally stable up to 250 °C. A detailed interpretation of the FT-IR, FT-Raman and NMR spectra were reported. The equilibrium geometry, bonding features, and harmonic vibrational frequencies have been investigated with the help of PM6, HF and DFT/B3LYP methods. The potential energy curve shows that MOX molecule has two stable structures and the computational results diagnose that Rot I is the most stable conformer. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge-Invariant Atomic Orbital (GIAO) method. Stability of the molecule, arising from hyperconjugative interactions and charge delocalization, has been analyzed using Natural Bond Orbital (NBO) analysis. The electronic properties, such as HOMO and LUMO energies, were calculated by Time-Dependent DFT (TD-DFT) approach. To estimate chemical reactivity of the molecule, the molecular electrostatic potential (MEP) surface map is calculated for the optimized geometry of the molecule.

Sangeetha, V.; Govindarajan, M.; Kanagathara, N.; Gunasekaran, S.; Rajakumar, P. R.; Anbalagan, G.

2014-06-01

72

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 78 K were recorded and depolarization data obtained. The infrared spectra of the vapour, liquid and amorphous and crystalline solids have been studied. In the low temperature IR and Raman spectra eight and three bands, respectively, were shifted a few cm(-1) when the sample crystallized. No bands vanished after crystallization in agreement with the assumption that only one conformer (chair) was present in all the states of aggregation. The compound exists in the stable chair conformation, whereas in the parent silacyclohexane a possible twist form should have more than 15 kJ mol(-1) higher energies than the chair, as derived from various calculations. The wavenumbers of the vibrational modes were calculated in the harmonic and anharmonic approximation employing B3LYP/cc-pVTZ calculations. The 27 A' and 21 A? fundamentals were assigned on the basis of the calculations, infrared vapour contours, Raman depolarization measurements and infrared and Raman band intensities. An average, relative deviation of 1.5% was found between the observed and the anharmonic wavenumbers for the 48 modes. PMID:24238936

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

2015-02-01

73

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

74

Conformational stability, r(0) 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 (4000-400 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. PMID:24618201

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

2015-02-01

75

Automatic generation of force fields and property surfaces for use in variational vibrational calculations of anharmonic vibrational energies and zero-point vibrational averaged properties.  

PubMed

An automatic and general procedure for the calculation of geometrical derivatives of the energy and general property surfaces for molecular systems is developed and implemented. General expressions for an n-mode representation are derived, where the n-mode representation includes only the couplings between n or less degrees of freedom. The general expressions are specialized to derivative force fields and property surfaces, and a scheme for calculation of the numerical derivatives is implemented. The implementation is interfaced to electronic structure programs and may be used for both ground and excited electronic states. The implementation is done in the context of a vibrational structure program and can be used in combination with vibrational self-consistent field (VSCF), vibrational configuration interaction (VCI), vibrational Moller-Plesset, and vibrational coupled cluster calculations of anharmonic wave functions and calculation of vibrational averaged properties at the VSCF and VCI levels. Sample calculations are presented for fundamental vibrational energies and vibrationally averaged dipole moments and frequency dependent polarizabilities and hyperpolarizabilities of water and formaldehyde. PMID:17014167

Kongsted, Jacob; Christiansen, Ove

2006-09-28

76

Automatic generation of force fields and property surfaces for use in variational vibrational calculations of anharmonic vibrational energies and zero-point vibrational averaged properties  

NASA Astrophysics Data System (ADS)

An automatic and general procedure for the calculation of geometrical derivatives of the energy and general property surfaces for molecular systems is developed and implemented. General expressions for an n-mode representation are derived, where the n-mode representation includes only the couplings between n or less degrees of freedom. The general expressions are specialized to derivative force fields and property surfaces, and a scheme for calculation of the numerical derivatives is implemented. The implementation is interfaced to electronic structure programs and may be used for both ground and excited electronic states. The implementation is done in the context of a vibrational structure program and can be used in combination with vibrational self-consistent field (VSCF), vibrational configuration interaction (VCI), vibrational Møller-Plesset, and vibrational coupled cluster calculations of anharmonic wave functions and calculation of vibrational averaged properties at the VSCF and VCI levels. Sample calculations are presented for fundamental vibrational energies and vibrationally averaged dipole moments and frequency dependent polarizabilities and hyperpolarizabilities of water and formaldehyde.

Kongsted, Jacob; Christiansen, Ove

2006-09-01

77

Molecular structure and vibrational spectra of o-chlorotoluene, m-chlorotoluene, and p-chlorotoluene by ab initio HF and DFT calculations  

NASA Astrophysics Data System (ADS)

In this work, experimental and theoretical study on the molecular structure and the vibrational spectra of o-chlorotoluene (OCT), m-chlorotoluene (MCT) and p-chlorotoluene (PCT) are presented. The vibrational frequencies of these compounds were obtained theoretically by ab initio HF and DFT/B3LYP calculations employing the standard 6-311++G(d,p) basis set for optimized geometries and were compared with Fourier transform infrared (FTIR) in the region of 400-4000 cm -1 and with Raman spectra in the region of 100-4000 cm -1. Complete vibrational assignment, analysis and correlation of the fundamental modes for these compounds have been carried out. The vibrational harmonic frequencies were scaled using scale factors, yielding a good agreement between the experimentally recorded and the theoretically calculated values.

Wang, Jidong; Ren, Mingmin; Wang, Shui; Qu, Yixin

2011-03-01

78

HOTB: High precision parallel code for calculation of four-particle harmonic oscillator transformation brackets  

NASA Astrophysics Data System (ADS)

This new version of the HOTB program for calculation of the three and four particle harmonic oscillator transformation brackets provides some enhancements and corrections to the earlier version (Germanas et al., 2010) [1]. In particular, new version allows calculations of harmonic oscillator transformation brackets be performed in parallel using MPI parallel communication standard. Moreover, higher precision of intermediate calculations using GNU Quadruple Precision and arbitrary precision library FMLib [2] is done. A package of Fortran code is presented. Calculation time of large matrices can be significantly reduced using effective parallel code. Use of Higher Precision methods in intermediate calculations increases the stability of algorithms and extends the validity of used algorithms for larger input values. Catalogue identifier: AEFQ_v4_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEFQ_v4_0.html Program obtainable from: CPC Program Library, Queen’s University of Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 Number of lines in programs, including test data, etc.: 1711 Number of bytes in distributed programs, including test data, etc.: 11667 Distribution format: tar.gz Program language used: FORTRAN 90 with MPI extensions for parallelism Computer: Any computer with FORTRAN 90 compiler Operating system: Windows, Linux, FreeBSD, True64 Unix Has the code been vectorized of parallelized?: Yes, parallelism using MPI extensions. Number of CPUs used: up to 999 RAM(per CPU core): Depending on allocated binomial and trinomial matrices and use of precision; at least 500 MB Catalogue identifier of previous version: AEFQ_v1_0 Journal reference of previous version: Comput. Phys. Comm. 181, Issue 2, (2010) 420-425 Does the new version supersede the previous version? Yes Nature of problem: Calculation of matrices of three-particle harmonic oscillator brackets (3HOB) and four-particle harmonic oscillator brackets (4HOB) in a more effective way, which allows us to calculate matrix of the brackets up to a few hundred times more rapidly and more accurate than in a previous version. Solution method: Using external parallelization libraries and mutable precision we created a pack of numerical codes based on the methods of compact expressions of the three and four-particle harmonics oscillator brackets 3HOB, 4HOB, presented in [3]. Restrictions: For double precision version calculations can be done up to harmonic oscillator (HO) energy quanta e=28. For quadruple precision mantissa is equal to approximately 34 decimal digits, therefore calculations can be done up to HO energy quanta to e=52. Running time: The running time depends on the harmonic oscillator energy quanta, cluster size and the precision of intermediate calculations. More information on Table 1 for 3HOB and Table 2 for 4HOB. Reasons for a new version: The new program version expands the limits of harmonic oscillator energy quanta and gives shorter calculation time. Extend the limits of calculation of HOB First version was able to produce harmonic oscillator transformation brackets for three and four particles if E?HO energy quanta. With this version of our program, if quadruple or arbitrary precision functions are being used, it is possible to calculate three and four particle harmonic oscillator transformation brackets for greater values of energy and momenta, while sustaining tolerable margin of error. Calculation time As the code of previous version of program was redone using parallelism paradigma, it is now possible to reduce the calculation time of transformation matrices significantly, depending on the size of computing cluster, as the dimensions of matrices are growing very rapidly according to the energy and momenta values. subroutinematrix_4HOB_dimensionCalculates the dimension of 4HOB matrix. subroutinematrix_3HOB_dimensionCalculates the dimension of 3HOB matrix, subroutinematrix_3HOBCalculates the global state array which is used in parallel calculation of 3HOB matrix. subroutinematrix_4HOBCalculates the global sta

Stepšys, A.; Mickevicius, S.; Germanas, D.; Kalinauskas, R. K.

2014-11-01

79

A simple state-average procedure determining optimal coordinates for anharmonic vibrational calculations  

NASA Astrophysics Data System (ADS)

A simple methodology for calculating state average energies in the context of vibrational self-consistent field (VSCF) is suggested. The suggested state average energy is employed in the optimization of coordinates for anharmonic vibrational wave function calculations where an orthogonal matrix of transformation between normal and optimized coordinates is variationally optimized. The convergence to the exact limit for approximate vibrational configuration interaction and vibrational coupled cluster wave functions is studied, comparing the performance of state average optimized coordinates, ground state optimized coordinates and standard normal coordinates. Exploratory calculations are presented for water, formaldehyde, the water dimer and trimer, and ethylene.

Thomsen, Bo; Yagi, Kiyoshi; Christiansen, Ove

2014-08-01

80

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

81

Vibrational dynamics of the bifluoride ion. III. F-F (?1) eigenstates and vibrational intensity calculations  

NASA Astrophysics Data System (ADS)

This paper concludes a theoretical study of vibrational dynamics in the bifluoride ion FHF-, which exhibits strongly anharmonic and coupled motions. Two previous papers have described an extended model potential surface for the system, developed a scheme for analysis based on a zero-order adiabatic separation of the proton bending and stretching motions (?2,?3) from the slower F-F symmetric-stretch motion (?1), and presented results of accurate calculations of the adiabatic protonic eigenstates. Here the ?1 motion has been treated, in adiabatic approximation and also including nonadiabatic couplings in close-coupled calculations with up to three protonic states (channels). States of the system involving more than one quantum of protonic excitation (e.g., 2?2, 2?3 ?g states; 3?2, ?2+2?3 ?u states; ?3+2?2, 3?3 ?u states) exhibit strong mixing at avoided crossings of protonic levels, and these effects are discussed in detail. Dipole matrix elements and relative intensities for vibrational transitions have been computed with an electronic dipole moment function based on ab initio calculations for an extended range of geometries. Frequencies, relative IR intensities and other properties of interest are compared with high resolution spectroscopic data for the gas-phase free ion and with the IR absorption spectra of KHF2(s) and NaHF2(s). Errors in the ab initio potential surface yield fundamental frequencies ?2 and ?3 100-250 cm-1 higher than those observed in either the free ion or the crystalline solids, but these differences are consistent and an unambiguous assignment of essentially all transitions in the IR spectrum of KHF2 is made. Calculated relative intensities for stretching mode (?3, ?u symmetry) transitions agree well with those observed in both KHF2 [e.g., bands (?3+n?1), (?3+2?2), (3?3), etc.] and the free ion (?3,?3+?1). Calculated intensities for bending mode (?2, ?u symmetry) transitions agree well with experiment for the ?2 fundamental in the free ion and KHF2(s), and for a ?u transition in KHF2 which we assign to ?2+2?3, but are far too small to explain the prominence of progression bands (?2+n?1) and especially the strong overtone 3?2 in the spectrum of KHF2(s). Intensity of the progression bands (?2+n?1) in KHF2 can be explained by hydrogen bonding between adjacent FHF- ions; in NaHF2(s) where such interaction is absent, the band (?2+?1) is 50-100 times weaker, in agreement with calculations. The relatively high intensity of the 3?2 band, which also appears strongly in NaHF2(s), remains the major unexplained feature of the bifluoride spectrum in these solids. Suggestions are made for further experiments on the FHF- and FDF- systems which could test predictions of this dynamical analysis.

Epa, V. C.; Thorson, W. R.

1990-09-01

82

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.  

PubMed

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. PMID:24096066

Renuga, S; Muthu, S

2014-01-24

83

Ab initio calculation of anharmonic vibrational states of polyatomic systems: Electronic structure combined with vibrational self-consistent field  

NASA Astrophysics Data System (ADS)

An algorithm for first-principles calculation of vibrational spectroscopy of polyatomic molecules is proposed, which combines electronic ab initio codes with the vibrational self-consistent field (VSCF) method, and with a perturbation-theoretic extension of VSCF. The integrated method directly uses points on the potential energy surface, computed from the electronic ab initio code, in the VSCF part. No fitting of an analytic potential function is involved. A key element in the approach is the approximation that only interactions between pairs of normal modes are important, while interactions of triples or more can be neglected. This assumption was found to hold well in applications. The new algorithm was applied to the fundamental vibrational excitations of H2O, Cl-(H2O), and (H2O)2, using the Möller-Plesset method for the electronic structure. The vibrational frequencies found are in very good accord with experiments. Estimates suggest that this electronic ab initio/VSCF approach should be feasible, with reasonable computational resources, for all-mode calculations of vibrational energies and wave functions for systems of up to 10-15 atoms. The new method can be also very useful for testing the accuracy of electronic structure codes by comparing with experimental vibrational spectroscopy.

Chaban, Galina M.; Jung, Joon O.; Gerber, R. Benny

1999-08-01

84

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

85

Vanillin and isovanillin: comparative vibrational spectroscopic studies, conformational stability and NLO properties by density functional theory calculations.  

PubMed

This study is a comparative analysis of FT-IR and FT-Raman spectra of vanillin (3-methoxy-4-hydroxybenzaldehyde) and isovanillin (3-hydroxy-4-methoxybenzaldehyde). The molecular structure, vibrational wavenumbers, infrared intensities, Raman scattering activities were calculated for both molecules using the B3LYP density functional theory (DFT) with the standard 6-311++G(??) basis set. The computed values of frequencies are scaled using multiple scaling factors to yield good coherence with the observed values. The calculated harmonic vibrational frequencies are compared with experimental FT-IR and FT-Raman spectra. The geometrical parameters and total energies of vanillin and isovanillin were obtained for all the eight conformers (a-h) from DFT/B3LYP method with 6-311++G(??) basis set. The computational results identified the most stable conformer of vanillin and isovanillin as in the "a" form. Non-linear properties such as electric dipole moment (?), polarizability (?), and hyperpolarizability (?) values of the investigated molecules have been computed using B3LYP quantum chemical calculation. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecules. PMID:22542395

Balachandran, V; Parimala, K

2012-09-01

86

Ab initio vibrational calculations for H2SO4 and H2SO4 x H2O: spectroscopy and the nature of the anharmonic couplings.  

PubMed

Vibrational frequencies for fundamental, overtone, and combination excitations of sulfuric acid (H2SO4) and of sulfuric acid monohydrate cluster (H2SO4 x H2O) are computed directly from ab initio MP2/TZP potential surface points using the correlation-corrected vibrational self-consistent field (CC-VSCF) method, which includes anharmonic effects. The results are compared with experiment. The computed transitions show in nearly all cases good agreement with experimental data and consistent improvement over the harmonic approximation. The CC-VSCF improvements over the harmonic approximation are largest for the overtone and combination excitations and for the OH stretching fundamental. The agreement between the calculations and experiment also supports the validity of the MP2/TZP potential surfaces. Anharmonic coupling between different vibrational modes is found to significantly affect the vibrational frequencies. Analysis of the mean magnitude of the anharmonic coupling interactions between different pairs of normal modes is carried out. The results suggest possible mechanisms for the internal flow of vibrational energy in H2SO4 and H2SO4 x H2O. PMID:16834003

Miller, Y; Chaban, G M; Gerber, R B

2005-07-28

87

Theoretical probation of FClCOCl2 molecular complex : Post Hartree-Fock studies on molecular structures, stabilities and vibrational harmonic frequencies  

NASA Astrophysics Data System (ADS)

Potential energy surfaces of the weak FClCO⋯Cl 2 complex were studied using ab initio post Hartree-Fock theory at the MP2 and MP4 levels with 6-311G(d) and 6-311G(2d) basis sets. Two minimum energy conformations, first-order transition state and two second-order transition structures were found. The minimum energy forms (C and T) are separated by a small (less than 0.5 kcal/mol) barrier. At the MP2/6-311G(d) level their relative stabilities amount to -0.63 and -0.60 kcal/mol for C and T conformers, respectively, where at the MP2/6-311G(2d) approximation stabilities of both forms rise to -1.09 and -1.21 kcal/mol. The harmonic vibrational frequencies were calculated and compared with available experimental data.

Nowek, Andrzej; Reddy, Shirisha; LeszczySki, Jerzy

1994-12-01

88

The Calculation of Electrical Parameters of Film Bulk Acoustic Wave Resonators from Vibrations of Layered  

E-print Network

The Calculation of Electrical Parameters of Film Bulk Acoustic Wave Resonators from Vibrations resonators (FBARs) are new generation of piezoelectric resonators with higher frequencies and manufacturing products for wireless communication applications, the FBAR technology are being extensively studied for new

Wang, Ji

89

Vibrational circular dichroism of 1-amino-2-propanol and 2-amino-1-propanol: experiment and calculation  

Microsoft Academic Search

The vibrational circular dichroism (VCD) spectra of (S)-1-amino-2-propanol and (S)-2-amino- 1-propanol in non-aqueous solution have been investigated. The vibrational frequencies, infrared intensities and VCD intensities have been calculated for all the hydrogen-bonded conformers with ab initio wave functions at a 6-31G(0.3) basis set level. The VCD intensities have been calculated with the vibronic coupling theory a priori formalism. Comparison of

Xinhua Qu; Mario J. Citra; N. Ragunathan; Teresa B. Freedman; Laurence A. Nafie

1994-01-01

90

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

91

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

92

Combined ab initio and anharmonic vibrational spectroscopy calculations for rare gas containing fluorohydrides, HRgF  

NASA Astrophysics Data System (ADS)

MP2 and CCSD(T) calculations are used to analyse the structures and vibrational spectra of HRgF molecules, where the rare gas atom is He, Ne, Ar, Kr, Xe or Rn. We extend the analysis of the vibrational spectra of these molecules to include anharmonic corrections for the most likely candidates for experimental detection, i.e., HArF, HKrF, HXeF, and their deuterated isotopomers. The anharmonic correlation-corrected vibrational self-consistent-field (CC-VSCF) calculations are used for this, and fundamental, overtone and combination frequencies and their absorption intensities are computed.

Lundell, Jan; Chaban, Galina M.; Benny Gerber, R.

2000-12-01

93

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

94

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

95

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

PubMed

The molecular structure of 2-(tert-butoxycarbonyl (Boc) -amino)-5-bromopyridine (BABP) was optimized by the DFT/B3LYP method with 6-311G (d,p), 6-311++G (d,p) and cc-pVTZ basis sets using the Gaussian 09 program. The most stable optimized structure of the molecule was predicted by the DFT/B3LYP method with cc-pVTZ basis set. The vibrational frequencies, Mulliken atomic charge distribution, frontier molecular orbitals and thermodynamical parameters were calculated. These calculations were done at the ground state energy level of BABP without applying any constraint on the potential energy surface. The vibrational spectra were experimentally recorded using Fourier Transform-Infrared (FT-IR) and micro-Raman spectrometer. The computed vibrational frequencies were scaled by scale factors to yield a good agreement with observed experimental vibrational frequencies. The complete theoretically calculated and experimentally observed vibrational frequencies were assigned on the basis of Potential Energy Distribution (PED) calculation using the VEDA 4.0 program. The vibrational modes assignments were performed by using the animation option of GaussView 05 graphical interface for Gaussian program. The Mulliken atomic charge distribution was calculated for BABP molecule. The molecular reactivity and stability of BABP were also studied by frontier molecular orbitals (FMOs) analysis. PMID:24727165

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

2014-08-14

96

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

97

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

98

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

99

On-the-fly ab intito calculations of anharmonic vibrational frequencies: Local-monomer theory and application to HCl clusters  

NASA Astrophysics Data System (ADS)

We present an on-the-fly quantum mechanical method to obtain anharmonic vibrational frequencies for molecular clusters. The basis for the method is the local-monomer model, a "divide and conquer" approach to theoretical spectroscopy, previously applied using full-dimensional surfaces [Y. Wang and J. M. Bowman, J. Chem. Phys. 134, 154510 (2011)]. The model consists of performing a local normal-mode analysis for each monomer in a cluster in the field of the surrounding monomers. Anharmonic vibrational frequencies are then determined for each monomer by numerically solving the Schrödinger equation in terms of the local coordinates using ab initio energies obtained directly. Residual monomer-monomer coupling is accounted for using the Hückel-coupling extension [Y. Wang and J. M. Bowman, J. Chem. Phys. 136, 144113 (2012)]. In addition to the direct local-monomer approach, we propose and demonstrate a composite ab initio technique to reduce computational costs for calculating the anharmonic frequencies of large clusters. This technique utilizes two ab initio methods, a lower level of theory to compute geometries and perform harmonic analyses and a subsequent higher level of theory to compute the energies used in the anharmonic frequency calculations. We demonstrate the on-the-fly approach on hydrogen chloride clusters ranging in size from the dimer to the hexamer. Comparisons of the theoretical frequencies are made to previous experiments. We find the method to be an effective and computationally efficient approach to compute anharmonic frequencies.

Mancini, John S.; Bowman, Joel M.

2013-10-01

100

Calculation of the energy levels and sizes of baryons with a noncentral harmonic potential  

E-print Network

It is considered that the effective interaction between any two quarks in a baryon can be approximately described by a simple harmonic potential. Also, it is made use of the nonrelativistic approximation. The problem is firstly solved in Cartesian coordinates in order to find the energy levels irrespective of their angular momenta and then it is also solved in polar cilindrical coordinates for taking into account the angular momenta of the levels. The only parameters used in the calculation are the constituent masses of quarks. By making a comparison between the two solutions the energies and the corresponding angular momenta (and parity) of almost all baryon levels are described. The agreement with the experimental data is quite impressive. The solution in Cartesian coordinates also produces some very important figures for the sizes of baryons and for the harmonic oscillator constant which is clearly related to confinement.

Mario Everaldo de Souza

2002-09-05

101

Improved calculations of the lowest vibrational transitions in HeH{sup +}  

SciTech Connect

More accurate variational calculations of the lowest three pure vibrational states (v=0,1,2) of the {sup 4}HeH{sup +} molecular ion have been carried out without assuming the Born-Oppenheimer approximation. In the calculations we included the complete set of {alpha}{sup 2} relativistic corrections, i.e., mass-velocity, Darwin, spin-spin, and orbit-orbit. This allowed us to improve the agreement between the theory and the experiment for the vibrational frequencies of the 1{yields}0 and 2{yields}1 transitions as compared to our previous calculations [Stanke et al., Phys. Rev. Lett. 96, 233002 (2006)].

Bubin, Sergiy [Department of Chemistry, University of Arizona, Tucson, Arizona 85721 (United States); Stanke, Monika [Department of Chemistry, University of Arizona, Tucson, Arizona 85721 (United States); Institute of Physics, Nicholas Copernicus University, ulica Grudziadzka 5, PL 87-100 Torun (Poland); Kedziera, Dariusz [Department of Chemistry, Nicholas Copernicus University, ulica Gagarina 7, PL 87-100 Torun (Poland); Adamowicz, Ludwik [Department of Chemistry, University of Arizona, Tucson, Arizona 85721 (United States); Department of Physics, University of Arizona, Tucson, Arizona 85721 (United States)

2007-08-15

102

Numerical Calculation Method for Prediction of Ground-borne Vibration near Subway Tunnel  

Microsoft Academic Search

This paper describes the development of prediction method for ground-borne vibration from railway tunnels. Field measurement was carried out both in a subway shield tunnel, in the ground and on the ground surface. The generated vibration in the tunnel was calculated by means of the train\\/track\\/tunnel interaction model and was compared with the measurement results. On the other hand, wave

Kiwamu Tsuno; Masaru Furuta; Kazuhisa Abe

2010-01-01

103

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

NASA Astrophysics Data System (ADS)

Rotation-vibration spectra of the nitric acid molecule, HNO3, are calculated for wavenumbers up to 7000 cm-1. Calculations are performed using a Hamiltonian expressed in internal curvilinear vibrational coordinates employing a hybrid variational-perturbation method. An initial potential energy surface (PES) and dipole moment function (DMF) are calculated 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-1 for frequencies in the fundamental bands and 0.4 cm-1 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 both the form of the absorption bands and fine details of the observed spectra, including the rotational structure of the vibrational bands and the numerous hot absorption band. Many of these hot bands are found to be missing from the compilation in HITRAN. A room temperature line list comprising 2 × 109 lines is computed.

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

2015-03-01

104

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

PubMed

Rotation-vibration spectra of the nitric acid molecule, HNO3, are calculated for wavenumbers up to 7000 cm(-1). Calculations are performed using a Hamiltonian expressed in internal curvilinear vibrational coordinates employing a hybrid variational-perturbation method. An initial potential energy surface (PES) and dipole moment function (DMF) are calculated 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(-1) for frequencies in the fundamental bands and 0.4 cm(-1) 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 both the form of the absorption bands and fine details of the observed spectra, including the rotational structure of the vibrational bands and the numerous hot absorption band. Many of these hot bands are found to be missing from the compilation in HITRAN. A room temperature line list comprising 2 × 10(9) lines is computed. PMID:25747083

Pavlyuchko, A I; Yurchenko, S N; Tennyson, Jonathan

2015-03-01

105

Anharmonic vibrational spectroscopy calculations for (NH3)(HF) and (NH3)(DF): fundamental, overtone, and combination transitions.  

PubMed

In order to study the effects of hydrogen bonding on the spectroscopic properties of (NH3)(HF) and (NH3)(DF) complexes, vibrational spectra (including fundamental, overtone and combination transitions) were calculated using the vibrational self consistent field (VSCF) method. This ab initio VSCF method accounts for both one-dimensional anharmonicity and pair-wise mode-mode couplings for all vibrational modes of the molecule, using points on the potential energy surface (at the MP2/TZP level of theory in this study). An analysis of the coupling strength shows surprisingly important coupling effects from pair-wise interactions not expected to be major. This indicates the benefits of including all pair-wise mode-mode couplings for weakly bound systems. Hydrogen bonding induces approximately 20% red shifts for the HF and DF stretch frequencies. The corrections due to anharmonicity for these modes are -6% and -5%, respectively. The anharmonic corrections for the intermolecular stretch of (NH3)(HF) and (NH3)(DF) are each about -5%. The NH3 umbrella motion has virtually no anharmonic correction in the complex, whereas free ammonia experiences a -15% correction. Also, the closing motion as well as the opening motion is restricted. The 1 + 1 combination transition of the proton stretching and intermolecular stretching modes has remarkably large intensity, larger even than the intensities for the first overtone of the proton stretching modes. The anharmonic frequency for the fundamental HF stretch, 3268 cm(-1), is in good agreement with the experimental gas phase result, 3215 cm(-1). A comparison to solid rare-gas matrix data shows that the VSCF frequencies are a consistent improvement over the harmonic approximation. The experimental data also support the use of the MP2 level of theory for the associated electronic structure calculations. PMID:19791384

Brindle, Carrie A; Chaban, Galina M; Gerber, R Benny; Janda, Kenneth C

2005-03-01

106

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

107

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

PubMed

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): C?N = 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?-N?C=177.8 (5); ?C?C?-N=110.4 (5);

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

108

Pyridine N-oxide/trichloroacetic acid complex in acetonitrile: FTIR spectra, anharmonic calculations and computations of 1-3D potential surfaces of O-H vibrations.  

PubMed

FTIR spectra of pyridine N-oxide and trichloroacetic acid H-bonded complex in acetonitrile were studied at 20 and 50°C. The calculations of equilibrium configurations of the complex and their IR spectra in harmonic- and anharmonic approximations were carried out at the level of B3LYP/cc-pVTZ/PCM. However both approximations turned out to be incompetent determining the frequency of the O-? stretching vibration. In order to reveal the causes of essential discrepancies between calculated and experimental data one-, two- and three-dimensional potential energy surfaces (PES) of the O-H…O bridge proton motion in the frame of fixed other atoms in the complex were calculated. The frequencies of O-H…O stretching and bending vibrations were calculated by numerical solution of the Schrödinger equation. It is shown that only the approach of proton motion on the 3D PES allows obtaining a good agreement between the calculated and the experimental values of the frequencies of the ?-? stretching vibrations. PMID:24373980

Pitsevich, G; Malevich, A; Doroshenko, I; Kozlovskaya, E; Pogorelov, V; Sablinskas, V; Balevicius, V

2014-01-01

109

Calculation of RDX molecular crystal geometry and vibrational frequencies under hydrostatic pressure  

NASA Astrophysics Data System (ADS)

First-principles calculations of the effects of hydrostatic pressure on RDX are performed using the all-electron CRYSTAL06 program. The lattice constants and optimized internal co-ordinates are simulanteously obtained at ambient pressure and hydrostatic pressure up to 4 GPa. A variety of density functionals and basis sets are used and presented for comparison. The vibrational frequencies as a function of pressure are also calculated and compared with previous gas-phase calculations.

Perger, Warren; Slough, Wil

2007-06-01

110

Calculation of rotor impedance for use in design analysis of helicopter airframe vibrations  

NASA Technical Reports Server (NTRS)

Excessive vibration is one of the most prevalent technical obstacles encountered in the development of new rotorcraft. The inability to predict these vibrations is primarily due to deficiencies in analysis and simulation tools. The Langley Rotorcraft Structural Dynamics Program was instituted in 1984 to meet long term industry needs in the area of rotorcraft vibration prediction. As a part of the Langley program, this research endeavors to develop an efficient means of coupling the rotor to the airframe for preliminary design analysis of helicopter airframe vibrations. The main effort was to modify the existing computer program for modeling the dynamic and aerodynamic behavior of rotorcraft called DYSCO (DYnamic System COupler) to calculate the rotor impedance. DYSCO was recently developed for the U.S. Army and has proven to be adaptable for the inclusion of new solution methods. The solution procedure developed to use DYSCO for the calculation of rotor impedance is presented. Verification of the procedure by comparison with a known solution for a simple wind turbine model is about 75 percent completed, and initial results are encouraging. After the wind turbine impedance is confirmed, the verification effort will continue by comparison to solutions of a more sophisticated rotorcraft model. Future work includes determination of the sensitivity of the rotorcraft airframe vibrations to helicopter flight conditions and rotor modeling assumptions. When completed, this research will ascertain the feasibility and efficiency of the impedance matching method of rotor-airframe coupling for use in the analysis of airframe vibrations during the preliminary rotorcraft design process.

Nygren, Kip P.

1990-01-01

111

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

112

Vibrational spectra of alkali metal cyclopentadienides and force field calculation of free cyclopentadienyl anion  

NASA Astrophysics Data System (ADS)

Raman and IR spectra have been studied in detail for lithium, sodium and potassium cyclopentadienides in solid state and their tetrahydrofuran (THF) and hexamethylphosphoric triamide (HMPA) solutions. The vibrational frequencies of cyclopentadienyl (Cp) anion have been obtained. The normal coordinate analysis of Cp-anion is presented. The force field of Cp-anion have been calculated by variation to a small extent of benzene force field, which reveals proximity of their electronic structures. Analysis of the low-frequency spectrum has shown that the interion stretching vibration dependent upon the cation mass is observed only in the IR spectrum, while the Raman spectrum exhibits the tilt doubly-degenerate vibration of Cp-ring in spite of the fact that both vibrations are allowed in both IR and Raman spectra.

Garkusha, O. G.; Garbuzova, I. A.; Lokshin, B. V.; Mink, J.

1988-05-01

113

High-order harmonic generation in vibrating two-electron molecules  

E-print Network

-active-electron (SAE) model. The isotope effect can be understood as follows. In general, the first step of the three¨odinger equation numerically, we simulate high-order harmonic generation from one-dimensional hydrogen molecules.C. Chirila) Preprint submitted to Elsevier September 29, 2009 #12;with electric field amplitude E0

Lein, Manfred

114

Uniformly accurate description of finite amplitude sound radiation from a harmonically vibrating planar boundary  

Microsoft Academic Search

The velocity potential for the two-dimensional, finite amplitude acoustic waves induced by harmonic excitation on a region in an infinite baffle was obtained by the author (1980). That analysis, which represented the response in terms of a continuous spectrum of wavenumbers parallel to the boundary, was valid only for limited distances from the boundary. The current analysis employs the perturbation

J. H. Ginsberg

1981-01-01

115

Calculation of the vibrational spectra of betaine hydrochloride  

Microsoft Academic Search

The molecular geometries of betaine hydrochloride, BET·HCl, and free protonated betaine, BET·H+, were calculated with the 6–31G(d,p) basis set at the SCF, MP2 and DFT levels of theory. At the SCF level, the minimum energy corresponds to the ionic pair, B+Htctdot;A?, however, the equilibrium Otctdot;Cl distance is 0.14 Å shorter than the X-ray value. Inclusion of the correlation effects, both

Miroslaw Szafran; Jacek Koput

1997-01-01

116

Vibrational absorption spectra from vibrational coupled cluster damped linear response functions calculated using an asymmetric Lanczos algorithm  

NASA Astrophysics Data System (ADS)

We report the theory and implementation of vibrational coupled cluster (VCC) damped response functions. From the imaginary part of the damped VCC response function the absorption as function of frequency can be obtained, requiring formally the solution of the now complex VCC response equations. The absorption spectrum can in this formulation be seen as a matrix function of the characteristic VCC Jacobian response matrix. The asymmetric matrix version of the Lanczos method is used to generate a tridiagonal representation of the VCC response Jacobian. Solving the complex response equations in the relevant Lanczos space provides a method for calculating the VCC damped response functions and thereby subsequently the absorption spectra. The convergence behaviour of the algorithm is discussed theoretically and tested for different levels of completeness of the VCC expansion. Comparison is made with results from the recently reported [P. Seidler, M. B. Hansen, W. Györffy, D. Toffoli, and O. Christiansen, J. Chem. Phys. 132, 164105 (2010)] vibrational configuration interaction damped response function calculated using a symmetric Lanczos algorithm. Calculations of IR spectra of oxazole, cyclopropene, and uracil illustrate the usefulness of the new VCC based method.

Thomsen, Bo; Hansen, Mikkel Bo; Seidler, Peter; Christiansen, Ove

2012-03-01

117

Vibrational absorption spectra from vibrational coupled cluster damped linear response functions calculated using an asymmetric Lanczos algorithm.  

PubMed

We report the theory and implementation of vibrational coupled cluster (VCC) damped response functions. From the imaginary part of the damped VCC response function the absorption as function of frequency can be obtained, requiring formally the solution of the now complex VCC response equations. The absorption spectrum can in this formulation be seen as a matrix function of the characteristic VCC Jacobian response matrix. The asymmetric matrix version of the Lanczos method is used to generate a tridiagonal representation of the VCC response Jacobian. Solving the complex response equations in the relevant Lanczos space provides a method for calculating the VCC damped response functions and thereby subsequently the absorption spectra. The convergence behaviour of the algorithm is discussed theoretically and tested for different levels of completeness of the VCC expansion. Comparison is made with results from the recently reported [P. Seidler, M. B. Hansen, W. Gyo?rffy, D. Toffoli, and O. Christiansen, J. Chem. Phys. 132, 164105 (2010)] vibrational configuration interaction damped response function calculated using a symmetric Lanczos algorithm. Calculations of IR spectra of oxazole, cyclopropene, and uracil illustrate the usefulness of the new VCC based method. PMID:22462829

Thomsen, Bo; Hansen, Mikkel Bo; Seidler, Peter; Christiansen, Ove

2012-03-28

118

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

NASA Technical Reports Server (NTRS)

Boeing Helicopters, together with other U.S. Helicopter manufacturers, participated in a finite element applications program to give the United States a superior capability to utilize finite element analysis models in support of helicopter airframe design. The program was sponsored by the NASA Langley Research Center. Under this program, an activity was sponsored to evaluate existing analysis methods applicable to calculate coupled rotor-airframe vibrations. The helicopter used in this evaluation was the AH-1G helicopter. The results of the Boeing Helicopters efforts are summarized. The planned analytical procedure is reviewed. Changes to the planned procedure are discussed, and results of the correlation study are presented.

Ditaranto, R. A.; Sankewitsch, V.

1989-01-01

119

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

120

Reduction of electromagnetic force harmonics in asynchronous traction motor by adapting the rotor slot number  

Microsoft Academic Search

The harmonics in electromagnetic force are a source of mechanical vibration and audible noise in an asynchronous traction motor. This paper describes an approach to reduce the force harmonics by changing the rotor slot number. Both the radial and tangential forces acting on the stator teeth are calculated by Maxwell stress tensor and their time harmonics are examined by the

Byung-Taek Kim; Byun-Il Kwon; Seung-Chan Park

1999-01-01

121

The vibrational spectra including matrix isolation, conformations and ab initio calculations of 4-azidobut-1-yne  

E-print Network

The vibrational spectra including matrix isolation, conformations and ab initio calculations of 4 nozzle IR matrix isolation spectra showed very small temperature variations and it was not possible are present in the liquid at room temperature and in the argon matrix at 12 K, whereas only three conformers

Sklenak, Stepan

122

Two-dimensional electronic and vibrational band structure of uniaxially strained graphene from ab initio calculations  

Microsoft Academic Search

We present an in-depth analysis of the electronic and vibrational band structure of uniaxially strained graphene by ab initio calculations. Depending on the direction and amount of strain, the Fermi crossing moves away from the K point. However, graphene remains semimetallic under small strains. The deformation of the Dirac cone near the K point gives rise to a broadening of

Marcel Mohr; Konstantinos Papagelis; Janina Maultzsch; Christian Thomsen

2009-01-01

123

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

124

Simple semiclassical adiabatic calculation of anharmonic cross constants of a vibrational spectral fit  

Microsoft Academic Search

A simple classical adiabatic procedure, implemented with an EBK semiclassical quantization, permits the calculation of first order cross anharmonic constants of a vibrational spectral fit and shows their dependence on the anharmonicity of the coupling and not on the intrinsic anharmonicity of the modes. These first order corrections are identical to those obtained with a quantum mechanical approach.

Victor Fairen; Vicente Lopez

1988-01-01

125

Vibrational spectroscopy investigation and density functional theory calculations on (E)-N'-(4-methoxybenzylidene) benzohydrazide.  

PubMed

The FT-IR, FT-Raman and UV-Vis spectra of the Schiff base compound (E)-N'-(4-methoxybenzylidene) benzohydrazide (MBBH) have been recorded and analyzed. The optimized geometrical parameters were calculated. The complete vibrational assignments were performed on the basis of TED of the vibrational modes, calculated with the help of SQM method. NBO analysis has been carried out to explore the hyperconjugative interactions and their second order stabilization energy within the molecule. The molecular orbitals (MO's) and its energy gap were studied. The first order hyperpolarizability (?0) and related properties (?, ?0, ??) of MBBH are also calculated. All theoretical calculations were performed on the basis of B3LYP/6-311++G(d,p) level of theory. PMID:25733250

Saleem, H; Subashchandrabose, S; Ramesh Babu, N; Syed Ali Padusha, M

2015-05-15

126

Evaluation of the effect of vibration nonlinearity on convergence behavior of adaptive higher harmonic controllers  

NASA Technical Reports Server (NTRS)

Effect of nonlinearity on convergence of the local linear and global linear adaptive controllers is evaluated. A nonlinear helicopter vibration model is selected for the evaluation which has sufficient nonlinearity, including multiple minimum, to assess the vibration reduction capability of the adaptive controllers. The adaptive control algorithms are based upon a linear transfer matrix assumption and the presence of nonlinearity has a significant effect on algorithm behavior. Simulation results are presented which demonstrate the importance of the caution property in the global linear controller. Caution is represented by a time varying rate weighting term in the local linear controller and this improves the algorithm convergence. Nonlinearity in some cases causes Kalman filter divergence. Two forms of the Kalman filter covariance equation are investigated.

Molusis, J. A.; Mookerjee, P.; Bar-Shalom, Y.

1983-01-01

127

Anharmonic vibrational calculations modeling the raman spectra of intermediates in the photoactive yellow protein (PYP) photocycle.  

PubMed

The role of anharmonic effects in the vibrational spectroscopy of the dark state and two major chromophore intermediates of the photoactive yellow protein (PYP) photocycle is examined via ab initio vibrational self-consistent field (VSCF) calculations and time-resolved resonance Raman spectroscopy. For the first time, anharmonicity is considered explicitly in calculating the vibrational spectra of an ensemble consisting of the PYP chromophore surrounded by model compounds used as mimics of the important active-site residues. Predictions of vibrational frequencies on an ab initio corrected semiempirical potential energy surface show remarkable agreement with experimental frequencies for all three states, thus shedding light on the potential along the reaction path. For example, calculated frequencies for vibrational modes of the red-shifted intermediate, PYPL, exhibit an overall average error of 0.82% from experiment. Upon analysis of anharmonicity patterns in the PYP modes we observe a decrease in anharmonicity in the C8-C9 stretching mode nu29 (trans-cis isomerization marker mode) with the onset of the cis configuration in PYPL. This can be attributed to the loss of the hydrogen-bonding character of the adjacent C9-O2 to the methylamine (Cys69 backbone). For several of the modes, the anharmonicity is mostly due to mode-mode coupling, while for others it is mostly intrinsic. This study shows the importance of the inclusion of anharmonicity in theoretical spectroscopic calculations, and the sensitivity of experiments to anharmonicity. The characterization of protein active-site residues by small molecular mimics provides an acceptable chemical structural representation for biomolecular spectroscopy calculations. PMID:17378558

Adesokan, Adeyemi A; Pan, Duohai; Fredj, Erick; Mathies, Richard A; Gerber, R Benny

2007-04-18

128

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

129

Fast vibrational self-consistent field calculations through a reduced mode-mode coupling scheme  

NASA Astrophysics Data System (ADS)

We present a new methodology to perform fast correlation-corrected vibrational self-consistent field (CC-VSCF) calculations using ab initio potential energy points calculated on the fly. Our method is based on the replacement of all-electron basis sets with a pseudo-potential basis for heavy atoms, and on an efficient reduction of the number of pair-coupling elements used in the CC-VSCF procedure. The method is applied to several test systems: H2O, NH3, and CH4, where it proves to be efficient, providing a speedup factor of 2 compared to a standard CC-VSCF calculation. We also apply our technique to the simulation of the vibrational spectrum of ethane and show that very accurate results can be obtained with a substantial speedup for this system.

Benoit, David M.

2004-01-01

130

Fast vibrational self-consistent field calculations through a reduced mode-mode coupling scheme.  

PubMed

We present a new methodology to perform fast correlation-corrected vibrational self-consistent field (CC-VSCF) calculations using ab initio potential energy points calculated on the fly. Our method is based on the replacement of all-electron basis sets with a pseudo-potential basis for heavy atoms, and on an efficient reduction of the number of pair-coupling elements used in the CC-VSCF procedure. The method is applied to several test systems: H2O, NH3, and CH4, where it proves to be efficient, providing a speedup factor of 2 compared to a standard CC-VSCF calculation. We also apply our technique to the simulation of the vibrational spectrum of ethane and show that very accurate results can be obtained with a substantial speedup for this system. PMID:15267890

Benoit, David M

2004-01-01

131

Calculation of vibrational infrared intensities and Raman activities using explicit anharmonic wave functions.  

PubMed

Methods for automatic computation of IR intensities and Raman activities are described using vibrational self-consistent field (VSCF) and vibrational configuration interaction (VCI) wave functions. Inclusion of effects due to anharmonicity in the potential energy and property surfaces are found to improve the results substantially as compared to experimental data. Sample calculations employing water and formaldehyde are presented, allowing for comparison between different vibrational methods. The convergence with respect to excitation level in VCI and the extent of mode coupling in the potential and property expansions is investigated. In addition, different electronic methods used for generating the potential and property surfaces, namely CCSD, CCSD(T), DFT/B3LYP, and DFT/CAM-B3LYP have been compared. Details of the potential and property surfaces may have significant effects on the IR and Raman intensities. PMID:17474728

Seidler, Peter; Kongsted, Jacob; Christiansen, Ove

2007-11-01

132

A comparison of semi-active damping control strategies for vibration isolation of harmonic disturbances  

NASA Astrophysics Data System (ADS)

Active vibration isolation systems are less commonly used than passive systems due to their associated cost and power requirements. In principle, semi-active isolation systems can deliver the versatility, adaptability and higher performance of fully active systems for a fraction of the power consumption. Various semi-active control algorithms have been suggested in the past, many of which are of the "on-off" variety. This paper studies the vibration isolation characteristics of four established semi-active damping control strategies, which are based on skyhook control and balance control. A semi-active damper is incorporated into a single-degree-of-freedom (s.d.o.f.) system model subject to base excitation. Its performance is evaluated in terms of the root-mean-square (r.m.s.) acceleration transmissibility, and is compared with those of a passive damper and an ideal skyhook damper. The results show that the semi-active system always provides better isolation at higher frequencies than a conventional passively damped system.

Liu, Y.; Waters, T. P.; Brennan, M. J.

2005-02-01

133

A comparison of filter diagonalisation methods with the Lanczos method for calculating vibrational energy levels  

NASA Astrophysics Data System (ADS)

In this Letter we compare two low-storage filter diagonalisation methods for calculating energy levels and compare both to the Lanczos algorithm. We are able to calculate energy levels in a high-lying window in the vibrational spectrum of H 2O with fewer matrix-vector products using the Lanczos algorithm than using the filter diagonalisation methods. We find that the Lanczos calculation is less costly and that the cost of building the Hamiltonian and overlap matrices in the filtered basis is excessive if one uses a non-Chebyshev discrete variable representation filter.

Huang, Shi-Wei; Carrington, Tucker

1999-10-01

134

Uniformly accurate description of finite amplitude sound radiation from a harmonically vibrating planar boundary  

NASA Astrophysics Data System (ADS)

The velocity potential for the two-dimensional, finite amplitude acoustic waves induced by harmonic excitation on a region in an infinite baffle was obtained by the author (1980). That analysis, which represented the response in terms of a continuous spectrum of wavenumbers parallel to the boundary, was valid only for limited distances from the boundary. The current analysis employs the perturbation method of renormalization to derive expressions for the pressure and particle velocity that are uniformly accurate up to the location where a shock forms. The response consists of radiative and evanescent waves, with nonlinearity being significant only for the former. The solution is described as inversions of Fourier cosine transforms which feature a straining transformation of the space-time coordinates. A quantitative example for the case of an intense high-frequency excitation is shown to lead to a sound beam in which the nonlinear distortion is asymmetrical between the compression and rarefaction phases.

Ginsberg, J. H.

1981-04-01

135

Vibrational spectra and DFT calculations of the vibrational modes of Schiff base C18H17N3O2  

NASA Astrophysics Data System (ADS)

The Schiff base 4-{[(1E)-(2-Hydroxyphenyl)methylidene]amino}-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (C18H17N3O2) is a synthetic compound with a variety of scientific and technological applications, such as clinic, analytic and pharmacologic. In this work FT-Raman spectrum and FT-infrared spectrum of C18H17N3O2 were investigated at 300 K. Vibrational wavenumber and wave vector have been predicted using Density Functional Theory (B3LYP) calculations with the 6-31 G(d,p) basis set. The description of the normal modes was performed by means of the potential energy distribution. A comparison with experiment allowed us to assign most of the normal modes of the crystal.

Antunes, J. A.; Silva, L. E.; Bento, R. R. F.; Teixeira, A. M. R.; Freire, P. T. C.; Faria, J. L. B.; Ramos, R. J.; Silva, C. B.; Lima, J. A.

2012-04-01

136

Identification of the (CO 2) 2 Dimer Vibrations in the ? 1, 2? 2 Region: Anharmonic Variational Calculations  

NASA Astrophysics Data System (ADS)

This paper aims at examination of the (CO2)2 spectral absorption profile retrieved from the room temperature CO2 collision-induced absorption (CIA) spectrum in the region of the ?1, 2?2 Fermi doublet. The assignment of (CO2)2 vibrations is discussed, paying due attention to high-resolution CARS observations in the regions of ?low and ?up. A variational solution of the anharmonic vibrational problem for the (CO2)2 dimer was obtained using an extended basis set consisting of harmonic and Morse oscillator wave functions. This allowed for a satisfactory description of the vibrational dimer ?1, 2?2 spectrum from first principles. In particular, we have succeeded in proving that the diffuse absorption band seen in the trough between the major Fermi-coupled CIA bands belongs to combinations of CO2 bending vibrations in a dimer.

Vigasin, A. A.; Huisken, F.; Pavlyuchko, A. I.; Ramonat, L.; Tarakanova, E. G.

2001-09-01

137

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

138

Vibrationally Averaged Long-Range Molecule-Molecule Dispersion Coefficients from Coupled-Cluster Calculations  

NASA Astrophysics Data System (ADS)

Recent years have seen increasing interest in the structure and dynamics of molecular clusters formed when a chromophore molecule such as CO_2, OCS or N_2O is solvated by number of He atoms and/or para-H_2 molecules. A key experimental probe of their behaviour is the shift of a chromophore's vibrational transition frequency which occurs when the solvent species are attached to it. Such shifts are driven by the changes in the solvent-chromophore interaction potential upon vibrational excitation of the probe molecule. While `conventional' supermolecule calculations can often provide realistic predictions of such changes in the potential well and repulsive wall region, they become increasingly unreliable for describing the weak interactions at long range where most of the solvent species in a large cluster are located. It is therefore important to have accurate relative-orientation and monomer-stretching dependent long-range C_6, C_8 and C10 dispersion coefficients to incorporate into the models for the interaction potential and for its dependence on the chromophore's vibrational state. This paper describes how those coefficients can be obtained from calculated monomer dipole, quadrupole, and octupole polarizabilities for imaginary frequencies, and by making use of the Casimir-Polder relation and angular momentum coupling to extract orientation-dependent quantities. The calculations are performed using a modified version of the ACES2 program system which allows the calculation of dipole, quadrupole and octupole polarizabilities at the EOM-CCSD level, and of static multipole moments using CCSD(T) calculations and adequate basis sets. For each relevant level of the chromophore, vibrational averaging is performed by calculating the imaginary frequency polarizabilities at judiciously chosen geometries and performing a numerical integration using the free-molecule vibrational wavefunction. Subsequent work will involve merging this long-range part of the potential with a short-range part obtained from 'conventional' CCSD(T) calculations and using it in PIMC simulations of cluster behaviour. H. Li, N. Blinov, P.-N. Roy and R.J. Le Roy, J. Chem. Phys. 130, 144305 (2009).

Schmidt, Matthew; Nooijen, Marcel

2011-06-01

139

Vibrational spectroscopic studies and computational calculations of 5-chloro-2-(3-chlorophenylcarbamoyl)phenylacetate  

NASA Astrophysics Data System (ADS)

The FT-IR and FT-Raman spectra of 5-chloro-2-(3-chlorophenylcarbamoyl)phenylacetate were studied. The vibrational wave numbers and corresponding vibrational assignments were examined theoretically using the Gaussian 03 set of quantum chemistry codes and the normal modes are assigned by Potential Energy Distribution calculations. The synthesis, elemental analysis and NMR values are presented. The red shift of the NH stretching wave number in the infrared spectrum from the computed wave number indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The first hyperpolarizability, infrared intensities and Raman activities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of nonlinear optics. The geometrical parameters of the title compound are in agreement with that of similar reported derivatives.

Madhavan, V. S.; Mary, Y. Sheena; Varghese, Hema Tresa; Panicker, C. Yohannan; Mathew, Samuel; Van Alsenoy, Christian; Vinsova, Jarmila

2012-04-01

140

Molecular structure, vibrational, electronic and thermal properties of 4-vinylcyclohexene by quantum chemical calculations.  

PubMed

The solid phase FT-IR and FT-Raman spectra of 4-vinylcyclohexene (abbreviated as 4-VCH) have been recorded in the region 4000-100cm(-1). The optimized molecular geometry and vibrational frequencies of the fundamental modes of 4-VCH have been precisely assigned and analyzed with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method at 6-311++G(d,p) level basis set. The theoretical frequencies were properly scaled and compared with experimentally obtained FT-IR and FT-Raman spectra. Also, the effect due the substitution of vinyl group on the ring vibrational frequencies was analyzed and a detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated total energy distribution (TED). The time dependent DFT (TD-DFT) method was employed to predict its electronic properties, such as electronic transitions by UV-Visible analysis, HOMO and LUMO energies, molecular electrostatic potential (MEP) and various global reactivity and selectivity descriptors (chemical hardness, chemical potential, softness, electrophilicity index). Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Atomic charges obtained by Mulliken population analysis and NBO analysis are compared. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures are also calculated. PMID:25795608

Nagabalasubramanian, P B; Periandy, S; Karabacak, Mehmet; Govindarajan, M

2015-06-15

141

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 35Cl2CS 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

142

Iterative active-space selection for vibrational configuration interaction calculations using a reduced-coupling VSCF basis  

NASA Astrophysics Data System (ADS)

We adapt a variation-perturbation method to perform vibrational configuration interaction (VCI) calculations on large molecular systems. Starting from a self-consistent vibrational wave function, we use the vibrational configuration interaction with perturbation selected interactions (VCIPSI) algorithm to select an active VCI space iteratively. We then extend this approach to use a reduced-coupling description of potential energy surfaces. The accuracy of the method is tested on methane and benzoic acid molecules. The significant reduction in the size of the VCI basis obtained using the VCIPSI scheme does not affect the quality of the computed vibrational frequencies and reduces computational time dramatically.

Scribano, Yohann; Benoit, David M.

2008-06-01

143

Calculations of the infrared and vibrational circular dichroism spectra of ethanol and its deuterated isotopomers  

SciTech Connect

The scaled quantum mechanical force field method together with the Stephens formalism for the evaluation of rotational strengths has been used to calculate infrared and vibrational circular dichroism (VCD) spectra of ethanol and its deuterated isotopomers. For the IR spectra, agreement between the calculated and experimental spectra is extremely good; the root-mean-square deviation between the calculated and experimental frequencies for all 12 isotopomers is 15 cm{sup {minus}1}. The calculated VCD spectra are also in good agreement with the experimental ones when the evaluation of the rotational strengths is carried out using the distributed origin gauge. Both the IR and VCD results confirm the earlier conjecture that the gauche conformer predominates over the trans, even though the trans has a slightly lower SCF energy.

Dothe, H.; Lowe, M.A. (Boston Univ., MA (USA)); Alper, J.S. (Univ. of Massachusetts, Boston (USA))

1989-09-07

144

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

145

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

146

Structural and vibrational properties of oxcarbazepine, an anticonvulsant substance by using DFT and SCRF calculations  

NASA Astrophysics Data System (ADS)

In this work, we have presented a structural and vibrational study on the properties in gas and aqueous solution phases of oxcarbazepine, a polymorphic anticonvulsant substance, combining the available IR and Raman spectra with Density Functional Theory (DFT) calculations. Two stable C1 and C2 forms for the title molecule were theoretically determined by using the hybrid B3LYP/6-31G* method. The integral equation formalism variant polarised continuum model (IEFPCM) was employed to study the solvent effects by means of the self-consistent reaction field (SCRF) method. The vibrational spectra for the two forms of oxcarbazepine were completely assigned together with two dimeric species also observed in the solid phase. The presences of the two C1 and C2 forms together with the two dimeric species are supported by the IR and Raman bands between 1424 and 125 cm-1. Here, the properties for both forms of oxcarbazepine are compared and discussed.

Ladetto, María F.; Márquez, María B.; Brandán, Silvia A.

2014-10-01

147

Calculations of intermode coupling constants and simulations of amide I, II, and III vibrational spectra of dipeptides  

NASA Astrophysics Data System (ADS)

Amide I, II, and III vibrations of polypeptides are important marker modes whose vibrational spectra can provide critical information on structure and dynamics of proteins in solution. The extent of delocalization and vibrational properties of amide normal mode can be described by the amide local mode frequencies and intermode coupling constants between a pair of amide local modes. To determine these fundamental quantities, the previous Hessian matrix reconstruction method has been generalized here and applied to the density functional theory results for various dipeptide conformers. The calculation results are then used to simulate IR absorption, vibrational circular dichroism, and 2D IR spectra of dipeptides. The relationships between dipeptide backbone conformations and these vibrational spectra are discussed. It is believed that the present computational method and results will be of use to quantitatively simulate vibrational spectra of complicated polypeptides beyond simple dipeptides

Choi, Jun-Ho; Cho, Minhaeng

2009-07-01

148

Vibrational spectroscopic and quantum chemical calculations of ( E)- N-Carbamimidoyl-4-((naphthalen-1-yl-methylene)amino)benzene sulfonamide  

NASA Astrophysics Data System (ADS)

FT-IR and FT-Raman spectra of ( E)- N-Carbamimidoyl-4-((naphthalen-1-yl-methylene)amino)benzene sulfonamide were recorded and analyzed. The vibrational wavenumbers were computing at various levels of theory. The data obtained from theoretical calculations are used to assign vibrational bands obtained experimentally. The results indicate that B3LYP method is able to provide satisfactory results for predicting vibrational frequencies and structural parameters. The calculated first hyperpolarizability is comparable with reported values of similar derivatives and is an attractive object for future studies of non-linear optics. The geometrical parameters of the title compound are in agreement with that of similar derivatives.

Chandran, Asha; Varghese, Hema Tresa; Mary, Y. Sheena; Panicker, C. Yohannan; Manojkumar, T. K.; Van Alsenoy, Christian; Rajendran, G.

2012-02-01

149

Infrared spectrum of HXeI revisited: anharmonic vibrational calculations and matrix isolation experiments  

NASA Astrophysics Data System (ADS)

Anharmonic correlation-corrected vibrational self-consistent-field (CC-VSCF) calculations are reported for the neutral HXeI molecule. Fundamental, overtone and combination frequencies and their absorption intensities are computed, and compared with previous and new experimental data from FTIR matrix isolation measurements. Agreement between experiment and calculations extend the identification of the HXeI molecule, and the calculations prove useful in aiding assignment of new observed transitions. The results show that especially the Xe-H bond of HXeI is highly anharmonic. While the agreement between theory and experiment is useful for assignment, quantitative discrepancies still remain due to the deficiency of MP2 theory to describe the highly anharmonic surface.

Lundell, Jan; Pettersson, Mika; Khriachtchev, Leonid; Räsänen, Markku; Chaban, Galina M.; Gerber, R. Benny

2000-05-01

150

Non-Born-Oppenheimer calculations of the pure vibrational spectrum of T2 including relativistic corrections  

NASA Astrophysics Data System (ADS)

We report very accurate calculations of the complete pure vibrational spectrum of the T2 molecule with an approach where the Born-Oppenheimer (BO) approximation is not assumed. As the considered states correspond to the zero total angular momentum, their non-BO wave functions are spherically symmetric and are expanded in terms of all-particle, one-center, spherically symmetric explicitly correlated Gaussian functions multiplied by even nonnegative powers of the internuclear distance. The nonrelativistic energies of the states obtained in the non-BO calculations are corrected for the relativistic effects of the order of ?2 (where ? is the fine structure constant) calculated as expectation values of the operators representing these effects.

Stanke, Monika; Adamowicz, Ludwik

2014-10-01

151

Non-Born-Oppenheimer calculations of the pure vibrational spectrum of T? including relativistic corrections.  

PubMed

We report very accurate calculations of the complete pure vibrational spectrum of the T2 molecule with an approach where the Born-Oppenheimer (BO) approximation is not assumed. As the considered states correspond to the zero total angular momentum, their non-BO wave functions are spherically symmetric and are expanded in terms of all-particle, one-center, spherically symmetric explicitly correlated Gaussian functions multiplied by even nonnegative powers of the internuclear distance. The nonrelativistic energies of the states obtained in the non-BO calculations are corrected for the relativistic effects of the order of ?(2) (where ? is the fine structure constant) calculated as expectation values of the operators representing these effects. PMID:25338891

Stanke, Monika; Adamowicz, Ludwik

2014-10-21

152

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

NASA Astrophysics Data System (ADS)

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)].

Benoit, David M.

2008-12-01

153

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

154

Accurate variational calculations and analysis of the HOCl vibrational energy spectrum  

NASA Astrophysics Data System (ADS)

Large scale variational calculations for the vibrational states of HOCl are performed using a recently developed, accurate ab initio potential energy surface. Three different approaches for obtaining vibrational states are employed and contrasted; a truncation/recoupling scheme with direct diagonalization, the Lanczos method, and Chebyshev iteration with filter diagonalization. The complete spectrum of bound states for nonrotating HOCl is computed and analyzed within a random matrix theory framework. This analysis indicates almost entirely regular dynamics with only a small degree of chaos. The nearly regular spectral structure allows us to make assignments for the most significant part of the spectrum, based on analysis of coordinate expectation values and eigenfunctions. Ground state dipole moments and dipole transition probabilities are also calculated using accurate ab initio data. Computed values are in good agreement with available experimental data. Some exact rovibrational calculations for J=1, including Coriolis coupling, are performed. The exact results are nearly identical with those obtained from the adiabatic rotation approximation and very close to those from the centrifugal sudden approximation, thus indicating a very small degree of asymmetry and Coriolis coupling for the HOCl molecule.

Skokov, Sergei; Qi, Jianxin; Bowman, Joel M.; Yang, Chao-Yie; Gray, Stephen K.; Peterson, Kirk A.; Mandelshtam, Vladimir A.

1998-12-01

155

On the number of significant mode-mode anharmonic couplings in vibrational calculations: Correlation-corrected vibrational self-consistent field treatment of di-, tri-, and tetrapeptides.  

PubMed

A computational study is made of the number of important anharmonic mode-mode couplings in the context of vibrational calculations for di-, tri-, and tetrapeptides. The method employed is the correlation-corrected vibrational self-consistent field (CC-VSCF) algorithm, which includes correlation effects between different vibrational modes. It is found that results of good accuracy can be obtained in calculations that include only N log N mode-mode coupling terms, where N is the number of modes. This simplification significantly accelerates CC-VSCF calculations for large molecules. A criterion based on the characteristics of the normal-mode displacements is employed to predict a priori unimportant coupling terms. The criterion is tested statistically using Spearman's rank correlation coefficient. The results are illustrated by calculations for several di-, tri-, and tetrapeptides using semiempirical PM3 potential surfaces. These results are analyzed and a statistical model for error estimation is given. The decrease in the number of included coupling from N(2) to N log N opens possibilities of anharmonic vibrational calculations for large peptides. PMID:18447509

Pele, Liat; Gerber, R Benny

2008-04-28

156

On the number of significant mode-mode anharmonic couplings in vibrational calculations: Correlation-corrected vibrational self-consistent field treatment of di-, tri-, and tetrapeptides  

NASA Astrophysics Data System (ADS)

A computational study is made of the number of important anharmonic mode-mode couplings in the context of vibrational calculations for di-, tri-, and tetrapeptides. The method employed is the correlation-corrected vibrational self-consistent field (CC-VSCF) algorithm, which includes correlation effects between different vibrational modes. It is found that results of good accuracy can be obtained in calculations that include only NlogN mode-mode coupling terms, where N is the number of modes. This simplification significantly accelerates CC-VSCF calculations for large molecules. A criterion based on the characteristics of the normal-mode displacements is employed to predict a priori unimportant coupling terms. The criterion is tested statistically using Spearman's rank correlation coefficient. The results are illustrated by calculations for several di-, tri-, and tetrapeptides using semiempirical PM3 potential surfaces. These results are analyzed and a statistical model for error estimation is given. The decrease in the number of included coupling from N2 to NlogN opens possibilities of anharmonic vibrational calculations for large peptides.

Pele, Liat; Gerber, R. Benny

2008-04-01

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

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

159

Lowest vibrational states of {sup 4}He{sup 3}He{sup +}: Non-Born-Oppenheimer calculations  

SciTech Connect

Very accurate quantum mechanical calculations of the first five vibrational states of the {sup 4}He{sup 3}He{sup +} molecular ion are reported. The calculations have been performed explicitly including the coupling of the electronic and nuclear motions [i.e., without assuming the Born-Oppenheimer (BO) approximation]. The nonrelativistic non-BO wave functions were used to calculate the {alpha}{sup 2} relativistic mass velocity, Darwin, and spin-spin interaction corrections. For the lowest vibrational transition, whose experimental energy is established with high precision, the calculated and the experimental results differ by only 0.16 cm{sup -1}.

Stanke, Monika; Bubin, Sergiy [Department of Chemistry, University of Arizona, Tucson, Arizona 85721 (United States); Kedziera, Dariusz [Department of Chemistry, Nicholaus Copernicus University, ul. Gagarina 7, PL 87-100 Torun (Poland); Molski, Marcin [Department of Theoretical Chemistry, Faculty of Chemistry, Adam Mickiewicz University, ul. Grunwaldzka 6, Poznan, PL 60-780 (Poland); Adamowicz, Ludwik [Department of Chemistry, University of Arizona, Tucson, Arizona 85721 (United States); Department of Physics, University of Arizona, Tucson, Arizona 85721 (United States)

2007-11-15

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

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

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.  

PubMed

In this study 3,3',4,4'-tetrachloroazobenzene (TCAB) was prepared and then characterized by infrared, Raman, multidimensional nuclear magnetic resonance (NMR) and ultraviolet-visible spectroscopies. The density functional theory (DFT) together with the 6-31G(*) and 6-311++G(**) basis sets were used to study the structures and vibrational properties of the two cis and trans isomers of TCAB. The harmonic vibrational wavenumbers for the optimized geometries were calculated at the same theory levels. A complete assignment of all the observed bands in the vibrational spectra of TCAB was performed combining the DFT calculations with the scaled quantum mechanical force field (SQMFF) methodology. The molecular electrostatic potentials, atomic charges, bond orders and frontier orbitals for the two isomers of TCAB were compared and analyzed. The comparison of the theoretical ultraviolet-visible spectrum with the corresponding experimental demonstrates a good concordance while the calculated (1)H and (13)C chemicals shifts are in good conformity with the corresponding experimental NMR spectra of TCAB in solution. The npp(*) transitions for both forms were studied by natural bond orbital (NBO) while the topological properties were calculated by employing Bader's Atoms in the Molecules (AIM) theory. This study shows that the cis and trans isomers exhibit different structural and vibrational properties and absorption bands. PMID:25106816

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

2015-01-01

163

Quantum Mechanical Calculations to Interpret Vibrational and NMR Spectra of Organic Compounds Adsorbed onto Mineral Surfaces  

NASA Astrophysics Data System (ADS)

Vibrational (e.g., ATR FTIR and Raman) and nuclear magnetic resonance (NMR) spectroscopies provide excellent information on the bonding and atomic environment of adsorbed organic compounds. However, interpretation of observed spectra collected for organic compounds adsorbed onto mineral surfaces can be complicated by the lack of comparable analogs of known structure and uncertainties about the mineral surface structure. Quantum mechanical calculations provide a method for testing interpretations of observed spectra because models can be built to mimic predicted structures, and the results are independent of experimental parameters (i.e., no fitting to data is necessary). In this talk, methodologies for modeling vibrational frequencies and NMR chemical shifts of adsorbed organic compounds are discussed. Examples included salicylic acid (as an analog for important binding functional groups in humic acids) adsorbed onto aluminum oxides, organic phosphoryl compounds that represent herbicides and bacterial extracellular polymeric substances (EPS), and ofloxacin (a common agricultural antibiotic). The combination of the ability of quantum mechanical calculations to predict structures, spectroscopic parameters and energetics of adsorption with experimental data on these same properties allows for more definitive construction of surface complex models.

Kubicki, J. D.

2008-12-01

164

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

165

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

NASA Astrophysics Data System (ADS)

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; Malaspina, D. C.; Granada, J. R.

2013-07-01

166

HOCl Ro-vibrational bound-state calculations for nonzero total angular momentum.  

PubMed

The Lanczos homogeneous filter diagonalization method has been employed to compute the HOCl ro-vibrational states for a range of total angular momenta (J = 0, 1, 5, 10, 11, 20, 30) on a newly developed ab initio potential energy surface by Nanbu et al. (J. Theor. Comput. Chem. 2002, 1, 263). For such computationally challenging calculations, a parallel computing strategy has been incorporated into our method to perform the matrix-vector multiplications. For the computed low bound states, a spectroscopic assignment has been made and the widely used approximate adiabatic rotation method has been tested for the broad range of total angular momenta for this deep-well system. Comparison of experimental results with exact quantum mechanical calculations for the selected far-infrared transitions involving the range of total angular momenta has been made possible for the first time. PMID:16623477

Zhang, Hong; Smith, Sean C; Nanbu, Shinkoh; Nakamura, Hiroki

2006-04-27

167

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

PubMed

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. PMID:23862950

Marquez Damian, J I; Malaspina, D C; Granada, J R

2013-07-14

168

First-principles calculation of geometry and anharmonic vibrational spectra of thioformamide and thioformamide-d2  

NASA Astrophysics Data System (ADS)

The equilibrium geometry of thioformamide HCSNH2 has been determined at the MP2 and CCSD (T) electron correlation levels under Cs symmetry constraints using triple-zeta basis sets up to cc-pVTZ. All optimized planar structures are true minima on the potential-energy surface and are characterized by the C-N bond length within 1.353-1.343Å, C-S distances of 1.656-1.628Å, and NCS angle between 125.7° and 125.9°. The wave number of the NH2 out-of-plane wagging mode computed in the harmonic approximation shows stronger dependence on the basis set rather than the electron correlation level and varies from 85.9cm-1 at CCSD (T)/cc-pVDZ level to 335cm-1 at MP2/aug-cc-pVTZ level. Anharmonic vibrational spectra of HCSNH2 and HCSND2 have been determined directly from the potential-energy surfaces computed at MP2 level in triple-zeta valence (TZV)(2df,2p) and TZV +(2df,2p) basis sets using vibrational self-consistent-field (VSCF) and correlation-corrected VSCF (CC-VSCF) methods. CC-VSCF wave numbers of fundamental, first overtone, and most intense combination transitions are reported for thioformamide and those of fundamentals for thioformamide-d2. The NH2 wagging (?12) mode is strongly anharmonic and its fundamentals have been computed at 406.9cm-1[TZV(2df,2p)] and 399.5cm-1[TZV+(2df,2p)], which is remarkably close to the experimental energy of 393cm-1. Anharmonically computed fundamentals of this mode in thioformamide-d2, 299.7cm-1[TZV(2df,2p)] and 299.6cm-1[TZV+(2df,2p)], are only ˜7cm-1 higher than the transition energy (293cm-1) observed in the gas phase spectrum of HCSND2. The first overtone of the NH2 wagging mode of thioformamide (?1202) has been calculated by CC-VSCF procedure at 830.8cm-1[TZV(2df,2p)] and 880.0cm-1[TZV+(2df,2p)], which implies "negative" (?1202>2*?1201) anharmonicity of this mode.

Kowal, Andrzej T.

2006-01-01

169

First-principles calculation of geometry and anharmonic vibrational spectra of thioformamide and thioformamide-d2.  

PubMed

The equilibrium geometry of thioformamide HCSNH2 has been determined at the MP2 and CCSD(T) electron correlation levels under C(s) symmetry constraints using triple-zeta basis sets up to cc-pVTZ. All optimized planar structures are true minima on the potential-energy surface and are characterized by the C-N bond length within 1.353-1.343 A, C-S distances of 1.656-1.628 A, and NCS angle between 125.7 degrees and 125.9 degrees . The wave number of the NH2 out-of-plane wagging mode computed in the harmonic approximation shows stronger dependence on the basis set rather than the electron correlation level and varies from 85.9 cm(-1) at CCSD(T)cc-pVDZ level to 335 cm(-1) at MP2/aug-cc-pVTZ level. Anharmonic vibrational spectra of HCSNH2 and HCSND2 have been determined directly from the potential-energy surfaces computed at MP2 level in triple-zeta valence (TZV)(2df,2p) and TZV+(2df,2p) basis sets using vibrational self-consistent-field (VSCF) and correlation-corrected VSCF (CC-VSCF) methods. CC-VSCF wave numbers of fundamental, first overtone, and most intense combination transitions are reported for thioformamide and those of fundamentals for thioformamide-d2. The NH2 wagging (nu12) mode is strongly anharmonic and its fundamentals have been computed at 406.9 cm(-1) [TZV(2df,2p)] and 399.5 cm(-1) [TZV+(2df,2p)], which is remarkably close to the experimental energy of 393 cm(-1). Anharmonically computed fundamentals of this mode in thioformamide-d2, 299.7 cm(-1) [TZV(2df,2p)] and 299.6 cm(-1) [TZV+(2df,2p)], are only approximately 7 cm(-1) higher than the transition energy (293 cm(-1)) observed in the gas phase spectrum of HCSND2. The first overtone of the NH2 wagging mode of thioformamide (nu12 (02)) has been calculated by CC-VSCF procedure at 830.8 cm(-1) [TZV(2df,2p)] and 880.0 cm(-1) [TZV+(2df,2p)], which implies "negative" (nu12 (02)>2*nu12 (01)) anharmonicity of this mode. PMID:16409033

Kowal, Andrzej T

2006-01-01

170

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

171

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

172

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.

173

Structural and vibrational properties of transition-metal oxides from first-principles calculations  

NASA Astrophysics Data System (ADS)

The calculation of the vibrational spectrum of minerals is of fundamental importance to assess their behavior (e.g. their elastic properties, or possible structural phase transitions) under the high-temperature, high-pressure conditions of the Earth’s interior. The ubiquitous presence of transition metals and the consequent importance of electronic correlations make the study of these materials quite difficult to approach with approximate DFT functionals (as LDA or GGA). The DFT+U, consisting in a Hubbard-modeled correction to the DFT energy functionals, has been successfully used to study the electronic, structural, and magnetic properties of several Fe-bearing minerals. However, the vibrational spectrum of these systems has never been determined entirely (frozen- phonon techniques are overly expensive except for zone-center phonons). In this work we introduce the extension of Density-Functional-Perturbation-Theory to DFT+U, that allows to efficiently compute the phonon spectrum of transition-metal compounds from their correlated ground states. A comparative analysis between the vibrational properties of MnO, FeO, CoO, and NiO (in the undistorted cubic cell) highlights a marked dependence of several features of their phonon spectrum on the occupancy of localized d orbitals and thus, on elec- tronic correlation. The new computational tool is also employed to evaluate the rhombohedral distortion of FeO (particularly abundant in the Earth’s lower mantle) and to assess the stability of its B1 phase in different conditions of pressure and temperature.

Cococcioni, M.; Floris, A.; Himmetoglu, B.

2010-12-01

174

DFT calculation of vibrational frequencies of clusters in GaAs and the Raman spectra  

NASA Astrophysics Data System (ADS)

We have calculated the vibrational frequencies of clusters of Ga and As atoms from the first principles using the density-functional theory (DFT) method and the local-density approximation (LDA). We find that the calculated value of 286.2 cm-1 for a linear cluster of Ga2As2 is very near the experimental value of 292 ± 4 cm-1. The calculated value of 289.4 cm-1 for Ga2As6 (dumb bell) cluster is indeed very near the experimental value. There are strong phonon correlations so that the cluster frequency is within the dispersion relation of the crystal LO value. There is a weak line in the experimental Raman spectrum at 268 cm-1 which is very near the value of 267.3 cm-1 calculated for the Ga2As (triangular) cluster. The weak lines corresponding to the linear bonds provide the strength to the amorphous samples. There are clusters of atoms in the glassy state of GaAs.

Radhika Devi, V.; Shrivastava, Keshav N.

2012-09-01

175

The vibrational behavior of silica clusters at the glass transition: Ab initio calculations and thermodynamic implications.  

PubMed

We present the results of a computational investigation with ab initio procedures of the structure-energy and vibrational properties of silica clusters in a dielectric continuum with dielectric constant ?=3.8, through density functional theory/B3LYP gas phase calculations coupled with a polarized continuum model approach [integral equation formalism applied to a polarized continuum (IEFPCM)] and those of the periodical structure D(6h) which leads to the ?-cristobalite polymorph of silica when subjected to symmetry operations with the same functional within the linear combination of atomic orbitals (LCAO) approximation and in the framework of Bloch's theorem. Based on the computed energies and vibrational features, an aggregate of the D(6h) network and the monomer locally ordered in the short-medium range and both present in the glass in a mutual arrangement lacking of spatial continuity reproduces satisfactorily the experimentally observed low T heat capacity and the deviation from the Debye T(3) law. Above T(g), the experimental heat capacity of the liquid is perfectly reproduced summing to the internal modes the translational and rotational contributions to the bulk heat capacity and subtracting the (acoustic) terms arising from coherent motion (no longer existent). PMID:20849179

Ottonello, G; Zuccolini, M Vetuschi; Belmonte, D

2010-09-14

176

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

177

Structural and vibrational properties of VO2 from DFT and DFT+U calculations  

NASA Astrophysics Data System (ADS)

Vanadium dioxide (VO2) undergoes a metal-insulator transition (MIT) at 340,from a metallic, high-temperature rutile phase to a insulating, low-temperature monoclinic phase. In thin films, the extremely fast switching times (˜100 femtoseconds) of the MIT have led to many suggested device applications. Understanding the MIT driving mechanism and the long-debated importance of electronic correlation is important to these developments. We have computed the relaxed geometry and phonon frequencies using DFT and DFT+U for both phases of VO2. The dependence of vibrational mode frequencies and oscillator strengths on the Hubbard U parameter and their sensitivity to the Born effective charges in the insulating monoclinic phase will be reported. The calculated frequencies for U=5 eV are in good agreement with recent experimental infrared micro-spectroscopy measurements on single crystal platelets of VO2 footnotetextT. J. Huffman et al., PRB, submitted.. Our results indicate that strong electron-electron correlation must be included to describe the vibrational properties.

Walter, Eric J.; Krakauer, Henry; Huffman, Tyler J.; Xu, Peng; Qazilbash, M. M.

2013-03-01

178

The Classical Harmonic Vibrations of the Atomic Centers of Mass with Micro Amplitudes and Low Frequencies Monitored by the Entanglement between the Two Two-level Atoms in a Single mode Cavity  

E-print Network

We study the entanglement dynamics of the two two-level atoms coupling with a single-mode polarized cavity field after incorporating the atomic centers of mass classical harmonic vibrations with micro amplitudes and low frequencies. We propose a quantitative vibrant factor to modify the concurrence of the two atoms states. When the vibrant frequencies are very low, we obtain that: (i) the factor depends on the relative vibrant displacements and the initial phases rather than the absolute amplitudes, and reduces the concurrence to three orders of magnitude; (ii) the concurrence increases with the increase of the initial phases; (iii) the frequency of the harmonic vibration can be obtained by measuring the maximal value of the concurrence during a small time. These results indicate that even the extremely weak classical harmonic vibrations can be monitored by the entanglement of quantum states.

Yong-Yi Huang

2013-12-08

179

Anharmonic force constant calculations  

Microsoft Academic Search

The relationship of the anharmonic force constants in curvilinear internal coordinates to the observed vibration-rotation spectrum of a molecule is reviewed. A simplified method of setting up the required non-linear coordinate transformations is described: this makes use of an L tensor, which is a straightforward generalization of the L matrix used in the customary description of harmonic force constant calculations.

A. R. Hoy; I. M. Mills; G. Strey

1972-01-01

180

Molecular structure, natural bond analysis, vibrational, and electronic spectra of aspartateguanidoacetatenickel(II), [Ni(Asp)(GAA)]·H2O: DFT quantum mechanical calculations  

NASA Astrophysics Data System (ADS)

The aspartateguanidoacetatenickel (II) complex, [Ni(Asp)(GAA)], was synthesized and structural analysis was performed by means of the experimental methods: determination of the C, H, N and O contents, thermogravimetry, infrared and Raman spectroscopy. DFT:B3LYP/6-311G(d, p) calculations have been performed giving optimized structure and harmonic vibrational wavenumbers. Second derivative of the FT-infrared, FT-Raman and Surface Raman Enhanced Scattering (SERS) spectra, and band deconvolution analysis were also performed. Features of the FT-infrared, FT-Raman and SERS confirmed theoretical structure prediction. Full assignment of the vibrational spectrum was also supported by a carefully analysis of the distorted geometries generated by the normal modes. The Natural Bond Orbital analysis (NBO) was also carried out as a way to study the Ni (II) hybridization leading to the pseudo planar geometry of the framework, and the extension of the atomic N and O hybrid orbital of the different amino acids in the bond formation. Bands of charge transfer and d-d transitions were assigned in the UV-Vis spectrum.

Ramos, J. M.; de M. Cruz, M. T.; Costa, A. C., Jr.; Ondar, G. F.; Ferreira, Glaucio B.; Raniero, L.; Martin, A. A.; Versiane, O.; Téllez Soto, C. A.

2012-11-01

181

Vibrational spectra, ab initio calculations, and assignments of the fundamentals of the C2v conformer of n-pentane  

NASA Astrophysics Data System (ADS)

Ab initio calculations of the relative energies, optimized geometries and vibrational spectrum of the four conformers of n-pentane have been completed, and a normal coordinate calculation performed to establish the nature of the observed molecular vibrations. From the Raman spectrum of the annealed crystal, in which only aa conformer bands are observable, an assignment of the observed bands to the fundamental vibrations of the aa conformer of C2v symmetry is proposed. The relative energy in the liquid of the ag conformer to the aa conformer is measured in the CCC bending region near 400 cm-1 using both n-pentane and n-pentane-d12, and is found to be 164 ± 10 cm-1, corresponding to 460 ± 28 cal mol-1 in excellent agreement with the results of earlier workers obtained by other measurements, but roughly half the value calculated ab initio at the highest level of approximation available in this investigation.

LaPlante, Arthur J.; Stidham, Howard D.; Guirgis, Gamil A.; Dukes, Horace W.

2012-09-01

182

First-principles calculation of H vibrational excitations at a dislocation core of Pd  

NASA Astrophysics Data System (ADS)

Palladium is an ideal system for understanding the behavior of hydrogen in metals. In Pd, H is located both in octahedral sites and in dislocation cores, which act as nanoscale H traps and form Cottrell atmospheres. Adjacent to a dislocation core, H experiences the largest possible distortion in ?-Pd . Ab initio density-functional theory computes the potential energy for a hydrogen in an octahedral site in ?-Pd and in a trap site at the core of a partial of an edge dislocation. The Pd partial dislocation core changes the environment for H, distorting the H-Pd bonding which changes the local potential, vibrational spectra, and inelastic form factor for an isolated H atom. The decrease in excitation energy is consistent with experiments, and the calculations predict distortions to the H wave function.

Lawler, Hadley M.; Trinkle, Dallas R.

2010-11-01

183

Elastic properties of self-supported circular thin copper films calculated from equilibrium thermal vibration.  

PubMed

Thermomechanical vibration of ultrathin, self-supported copper films due to thermal fluctuations is studied via the molecular dynamics simulation at room temperature. The elastodynamic theory with pre-stress is adopted to extract the physical properties of the films by comparing with the molecular dynamics data. The edge-clamped circular films consist of several atomic layers of fcc copper with the [100] direction normal to the film surface. From the time-history trajectories of atoms and their Fourier frequency spectrums, it was found that the fundamental resonant frequency non-monotonically varies with the film thickness due to the existence of residual stress in the film. Multiple resonant modes are adopted for modulus calculation and residual stress determination. The value of Young's modulus increases with increasing thickness of the film and the residual stress decreases with increasing thickness. Thicker films exhibit less residual stress, indicating the equilibrium distance between copper atoms changes with the film thickness. PMID:21770113

Chang, Hsi-Hung; Hwang, Chi-Chuan; Shen, Yue-Ling

2011-06-01

184

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

185

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

186

Extending the vibrational self-consistent method: Using a partially separable wave function for calculating anharmonic vibrational states of polyatomic molecules  

NASA Astrophysics Data System (ADS)

A new method for the treatment of correlation effects between modes in vibrational self-consistent-field (VSCF) calculations is introduced. It is based upon using a partially separable form for the wave function. As a result, some of the modes are treated as mutually fully correlated, while the rest are separable. The modes which are explicitly coupled together in the calculation are chosen on physical grounds. Trial calculations are performed upon H2O, H3O+, and CH3NH2 and indicate that the method performs well. The agreement with experiment for the explicitly coupled modes is improved when compared to both the vibrational self-consistent-field method and its correlation-corrected extension. When interfaced with an electronic structure code this method opens the way for the accurate first-principles prediction of vibrational frequencies of strongly coupled modes. If only a few modes are mutually strongly coupled, the method has a very favorable scaling with system size, as does VSCF itself.

Wright, Nicholas J.; Gerber, R. Benny

2001-05-01

187

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

188

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

189

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

190

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

PubMed

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, 1,040-1,160 cm(-1) and 3,300-3,360 cm(-1) and pH dependence of the linewidth, peak position and intensity of the Raman bands corresponding to the ring breathing and symmetric nu(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 nu(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 nu(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. PMID:18396452

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

2008-12-01

191

A comment on recent proposals for the calculation of vibration-rotation energies in more-than-three atom molecules  

NASA Astrophysics Data System (ADS)

In a recent paper (Molec. Phys. 1991, 73, 1183), Bramley et al. analysed the physical and mathematical context in which the vibrational rotational Hamiltonian operator for a molecule is expressed in terms of Euler angles for the rotation and internal curvilinear coordinates for the vibration. In the case of a generic tetra-atomic molecule, they derived a few rules which determine the choice of the basis functions, in order (i) to ensure continuity and single-valuedness of the eigenfunctions and (ii) to cancel out the singularities (infinite integrals) that unavoidably crop up in the matrix representation of the vibration-rotation kinetic energy operator. In another recent paper (Phys. Rev.A, 1992, 45, 6217), Chapuisat and lung considered the vibration-rotation of a polyatomic molecule as resulting from the rotational-vibrational motion of coupled relative vectors; with the help of a standard representation for the angular motion of each vector viewed in the moving frame resulting from the first two Euler rotations, i.e. for the whole molecule a direct product of spherical harmonics, they have shown that it is possible to get rid of the singularities and to derive, after completing the third Euler rotation, analytical expressions of the kinetic energy operator matrix elements in the usual bending-torsion-rotation basis. In implementing this approach, the rules derived for tetraatomics by Bramley et al. are confirmed and are next generalized to the case of the N-atom molecule. The restrictions to the direct product representation which must be explicitly taken into account are established on the basis of a purely physical analysis of the coupled vector motion.

Chapuisat, Xavier; Belafhal, Abdelmajid; Nauts, André; Iung, Christophe

192

Communication: Towards the binding energy and vibrational red shift of the simplest organic hydrogen bond: Harmonic constraints for methanol dimer  

SciTech Connect

The discrepancy between experimental and harmonically predicted shifts of the OH stretching fundamental of methanol upon hydrogen bonding to a second methanol unit is too large to be blamed mostly on diagonal and off-diagonal anharmonicity corrections. It is shown that a decisive contribution comes from post-MP2 electron correlation effects, which appear not to be captured by any of the popular density functionals. We also identify that the major deficiency is in the description of the donor OH bond. Together with estimates for the electronic and harmonically zero-point corrected dimer binding energies, this work provides essential constraints for a quantitative description of this simple hydrogen bond. The spectroscopic dissociation energy is predicted to be larger than 18 kJ/mol and the harmonic OH-stretching fundamental shifts by about ?121 cm{sup ?1} upon dimerization, somewhat more than in the anharmonic experiment (?111 cm{sup ?1})

Heger, Matthias; Suhm, Martin A.; Mata, Ricardo A., E-mail: rmata@gwdg.de [Georg-August-Universität Göttingen, Institut für Physikalische Chemie, Tammannstr. 6, 37077 Göttingen (Germany)

2014-09-14

193

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

194

Vibrational self-consistent field calculations for spectroscopy of biological molecules: new algorithmic developments and applications.  

PubMed

This review describes the vibrational self-consistent field (VSCF) method and its other variants for computing anharmonic vibrational spectroscopy of biological molecules. The superiority and limitations of this algorithm are discussed with examples. The spectroscopic accuracy of the VSCF method is compared with experimental results and other available state-of-the-art algorithms for various biologically important systems. For large biological molecules with many vibrational modes, the scaling of computational effort is investigated. The accuracy of the vibrational spectra of biological molecules using the VSCF approach for different electronic structure methods is also assessed. Finally, a few open problems and challenges in this field are discussed. PMID:23677257

Roy, Tapta Kanchan; Gerber, R Benny

2013-06-28

195

Calculations of vibrationally resonant sum- and difference-frequency-generation spectra of chiral molecules in solutions: Three-wave-mixing vibrational optical activity  

NASA Astrophysics Data System (ADS)

Determining absolute configuration of chiral molecule can be achieved by using vibrational optical activity (VOA) measurement methods, such as vibrational circular dichroism and Raman optical activity (ROA). Recently, vibrationally resonant sum frequency generation and difference frequency generation utilizing circularly polarized beams were theoretically studied and shown that they can be alternative and complementary VOA measurement techniques [S. Cheon and M. Cho, Phys. Rev. A 71, 013808 (2005); J. Phys. Chem. A 113, 2438 (2009)]. Even for randomly oriented chiral molecules in solutions, the sum- and difference-frequency-generation signals induced by linearly polarized incident beams with mutually perpendicular polarization directions can be nonzero and are determined by the optical activity hyperpolarizability given by a product of antisymmetric Raman tensor and vibrational transition dipole. If one of the beams involved in the three-wave-mixing processes is circularly polarized and if the difference signal is measured, not only the same optical activity hyperpolarizability but also that including electric quadrupole-ROA tensor are required to determine the signals. Here, we carried out quantum chemistry calculations to obtain these quantities for a representative chiral molecule, (S)-methyl lactate, and numerically simulated the corresponding spectra. It is shown that the circular polarization three-wave-mixing signal intensities are quantitatively similar to those of the linear polarization three-wave-mixing signals, respectively, and that they are sensitive to the absolute configuration of chiral molecule. The calculation results thus suggest that these two novel techniques will be of use in studying molecular chirality even in time domain, once polarization-modulated ultrashort pulses are used to carry out circular polarization three-wave-mixing experiments.

Choi, Jun-Ho; Cheon, Sangheon; Cho, Minhaeng

2010-02-01

196

Vibrational spectroscopy of trans and cis deuterated formic acid (HCOOD): Anharmonic calculations and experiments in argon and neon matrices  

NASA Astrophysics Data System (ADS)

The absorption spectra of trans and cis conformers of deuterated formic acid (HCOOD) isolated in argon and neon matrices are analyzed in the mid-infrared and near-infrared spectral regions (7900-450 cm -1). Vibrational excitation by narrow-band IR radiation is used to convert the lower-energy trans conformer to the higher-energy cis form. A large number of overtone and combination bands are identified. The results of anharmonic vibrational calculations (CC-VSCF) for both conformers are reported and compared to the experimental spectra.

Marushkevich, K.; Khriachtchev, L.; Lundell, J.; Domanskaya, A. V.; Räsänen, M.

2010-02-01

197

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

198

Vibrational Spectra of Water Solutions of Azoles from QM/MM Calculations: Effects of Solvation  

E-print Network

the structural and dynamical aspects of water solutions. X-ray as well as neutron diffraction are the main source quantum/classical ab initio molecular dynamics simulations, we investigate the vibrational properties on the solute structure following how vibrational properties of molecules change in presence of solvent

Guidoni, Leonardo

199

Empirical Maps For The Calculation of Amide I Vibrational Spectra of Proteins From Classical Molecular Dynamics Simulations  

PubMed Central

New sets of parameters (maps) for calculating amide I vibrational spectra for proteins through a vibrational exciton model are proposed. The maps are calculated as a function of electric field and van der Waals forces on the atoms of peptide bonds, taking into account the full interaction between peptide bonds and the surrounding environment. The maps are designed to be employed using data obtained from standard all-atom molecular simulations without any additional constraints on the system. Six proteins representing a wide range of sizes and secondary structure complexity were chosen as a test set. Spectra calculated for these proteins reproduce experimental data both qualitatively and quantitatively. The proposed maps lead to spectra that capture the weak second peak observed in proteins containing ?-sheets, allowing for clear distinction between ?-helical and ?-sheet proteins. While the parametrization is specific to the CHARMM force field, the methodology presented can be readily applied to any empirical force field. PMID:24654732

2015-01-01

200

A calculation method for torsional vibration of a crankshafting system with a conventional rubber damper by considering rubber form  

SciTech Connect

The cheap and compact rubber dampers of shear-type have been widely employed as the torsional vibration control of the crankshaft system of high-speed, automobile diesel engines. The conventional rubber dampers have various rubber forms owing to the thorough investigation of optimum dampers in the design stage. Their rubber forms can be generally grouped into three classes such as the disk type, the bush type and the composite type. The disk type and the bush type rubber dampers are called the basic-pattern rubber dampers hereafter. The composite type rubber part is supposed to consist of the disk type and the bush type parts, regarded respectively as the basic patterns of the rubber part, at large. The dynamic characteristics of the vibration isolator rubber depend generally on temperature, frequency, strain amplitude, shape and size effect,s so it is difficult to estimate accurately their characteristics. With the present technical level, it is also difficult to determine the suitable rubber geometry which optimizes the vibration control effect. The study refers to the calculation method of the torsional vibration of a crankshaft system with a shear-type rubber damper having various rubber forms in order to offer the useful method for optimum design. In this method, the rheological formula of the three-element Maxwell model, from which the torsional stiffness and the damping coefficient of the damper rubber part in the equivalent vibration system are obtained, are adopted in order to decide the dynamic characteristics of the damper rubber part.

Kodama, Tomoaki; Honda, Yasuhiro; Wakabayashi, Katsuhiko; Iwamoto, Shoichi

1996-09-01

201

On quadrupole vibrations in nearly spherical nuclei  

NASA Astrophysics Data System (ADS)

A new understanding of low-lying quadrupole vibrations in nuclei is emerging through lifetime measurements performed with fast neutrons at the accelerator laboratory of the University of Kentucky in combination with high-sensitivity measurements with other probes. In the stable cadmium nuclei, which have long been considered to be the best examples of vibrational behavior, we find that many E2 transition probabilities are well below harmonic vibrator expectations, and the B(E2)s cannot be explained with calculations incorporating configuration mixing between vibrational phonon states and intruder excitations. These data place severe limits on the collective models, and it is suggested that the low-lying levels of the Cd isotopes may not be of vibrational origin. An additional example of an apparent quadrupole vibrational nucleus, 62Ni, is considered.

Yates, S. W.

2012-09-01

202

Path Integral Approach to the Calculation of Reaction Rates for a Reaction Coordinate Coupled to a Dual Harmonic Bath  

E-print Network

We present a new method for the numerical calculation of canonical reaction rate constants in complex molecular systems, which is based on a path integral formulation of the flux-flux correlation function. Central is the partitioning of the total system into a relevant part coupled to a dual bath. The latter consists of two parts: First, a set of strongly coupled harmonic modes, describing, for example, intramolecular degrees of freedom. They are treated on the basis of a reaction surface Hamiltonian approach. Second, a set of bath modes mimicking an unspecific environment modeled by means of a continuous spectral density. After deriving a set of general equations expressing the canonical rate constant in terms of appropriate influence functionals, several approximations are introduced to provide an efficient numerical implementation. Results for an initial application to the H-transfer in 6-Aminofulvene-1-aldimine are discussed.

Yonggang Yang; Oliver Kühn

2011-11-13

203

Surface-induced alteration of adsorbate electronic structure and intramolecular vibrational coupling: The vibrational spectrum of 2-propoxide on Mo(110) as determined by [ital ab] [ital initio] calculations and experiments  

SciTech Connect

Interactions with the molybdenum surface have a strong influence on the vibrational spectrum of 2-propoxide on Mo(110). Using [ital ab] [ital initio] electronic-structure calculations the vibrational spectrum of the adsorbed 2-propoxide is determined. All major effects, experimentally observed by electron-energy-loss spectroscopy, are well reproduced by the calculation. Kinematic effects do not explain the observed changes. Calculations indicate that the changes in vibrational spectra are due to alterations of the intramolecular potential function and charge redistribution upon binding to the Mo.

Uvdal, P. (MAX-Chemistry, Department of Chemistry, Box 124, Lund University, S-22100 Lund (Sweden)); MacKerell, A.D. Jr. (Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland at Baltimore, Baltimore, Maryland 21201 (United States)); Wiegand, B.C.; Friend, C.M. (Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138 (United States))

1995-03-15

204

Calculation of vibrational frequencies through a variational reduced-coupling approach  

NASA Astrophysics Data System (ADS)

In this study, we present a new method to perform accurate and efficient vibrational configuration interaction computations for large molecular systems. We use the vibrational self-consistent field (VSCF) method to compute an initial description of the vibrational wave function of the system, combined with the single-to-all approach to compute a sparse potential energy surface at the chosen ab initio level of theory. A Davidson scheme is then used to diagonalize the Hamiltonian matrix built on the VSCF virtual basis. Our method is applied to the computation of the OH-stretch frequency of formic acid and benzoic acid to demonstrate the efficiency and accuracy of this new technique.

Scribano, Yohann; Benoit, David M.

2007-10-01

205

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

206

Faraday Discuss., 1994,99, 121-129 Basis Set Convergenceand Correlation Effects in Vibrational  

E-print Network

. Introduction In the harmonic approximation, IR absorption intensities and vibrational circular dichroism (VCD Circular Dichroism Calculations using London Atomic Orbitals Keld L. Bak Department of Physical ChemistryFaraday Discuss., 1994,99, 121-129 Basis Set Convergenceand Correlation Effects in Vibrational

Helgaker, Trygve

207

Full Dimensional Vibrational Calculations for Methane Using AN Accurate New AB Initio Based Potential Energy Surface  

NASA Astrophysics Data System (ADS)

New potential energy surfaces for methane were constructed, represented as analytic fits to about 100,000 individual high-level ab initio data. Explicitly-correlated multireference data (MRCI-F12(AE)/CVQZ-F12) were computed using Molpro [1] and fit using multiple strategies. Fits with small to negligible errors were obtained using adaptations of the permutation-invariant-polynomials (PIP) approach [2,3] based on neural-networks (PIP-NN) [4,5] and the interpolative moving least squares (IMLS) fitting method [6] (PIP-IMLS). The PESs were used in full-dimensional vibrational calculations with an exact kinetic energy operator by representing the Hamiltonian in a basis of products of contracted bend and stretch functions and using a symmetry adapted Lanczos method to obtain eigenvalues and eigenvectors. Very close agreement with experiment was produced from the purely ab initio PESs. References 1- H.-J. Werner, P. J. Knowles, G. Knizia, 2012.1 ed. 2012, MOLPRO, a package of ab initio programs. see http://www.molpro.net. 2- Z. Xie and J. M. Bowman, J. Chem. Theory Comput 6, 26, 2010. 3- B. J. Braams and J. M. Bowman, Int. Rev. Phys. Chem. 28, 577, 2009. 4- J. Li, B. Jiang and Hua Guo, J. Chem. Phys. 139, 204103 (2013). 5- S Manzhos, X Wang, R Dawes and T Carrington, JPC A 110, 5295 (2006). 6- R. Dawes, X-G Wang, A.W. Jasper and T. Carrington Jr., J. Chem. Phys. 133, 134304 (2010).

Majumder, Moumita; Dawes, Richard; Wang, Xiao-Gang; Carrington, Tucker; Li, Jun; Guo, Hua; Manzhos, Sergei

2014-06-01

208

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

209

Study of conformational stability, structural, electronic and charge transfer properties of cladrin using vibrational spectroscopy and DFT calculations  

NASA Astrophysics Data System (ADS)

In the present work, a detailed conformational study of cladrin (3-(3,4-dimethoxy phenyl)-7-hydroxychromen-4-one) has been done by using spectroscopic techniques (FT-IR/FT-Raman/UV-Vis/NMR) and quantum chemical calculations. The optimized geometry, wavenumber and intensity of the vibrational bands of the cladrin in ground state were calculated by density functional theory (DFT) employing 6-311++G(d,p) basis sets. The study has been focused on the two most stable conformers that are selected after the full geometry optimization of the molecule. A detailed assignment of the FT-IR and FT-Raman spectra has been done for both the conformers along with potential energy distribution for each vibrational mode. The observed and scaled wavenumber of most of the bands has been found to be in good agreement. The UV-Vis spectrum has been recorded and compared with calculated spectrum. In addition, 1H and 13C nuclear magnetic resonance spectra have been also recorded and compared with the calculated data that shows the inter or intramolecular hydrogen bonding. The electronic properties such as HOMO-LUMO energies were calculated by using time-dependent density functional theory. Molecular electrostatic potential has been plotted to elucidate the reactive part of the molecule. Natural bond orbital analysis was performed to investigate the molecular stability. Non linear optical property of the molecule have been studied by calculating the electric dipole moment (?) and the first hyperpolarizability (?) that results in the nonlinearity of the molecule.

Singh, Swapnil; Singh, Harshita; Srivastava, Anubha; Tandon, Poonam; Sinha, Kirti; Bharti, Purnima; Kumar, Sudhir; Kumar, Padam; Maurya, Rakesh

2014-11-01

210

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

PubMed

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(*) 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(*) 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(*) data show excellent agreement with the experimental data in terms of IS and CFS in region II; however, PBE-D(*) 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(*). PMID:24811648

Zhang, Feng; Hayashi, Michitoshi; Wang, Houng-Wei; Tominaga, Keisuke; Kambara, Ohki; Nishizawa, Jun-ichi; Sasaki, Tetsuo

2014-05-01

211

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

NASA Astrophysics Data System (ADS)

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* 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* 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* data show excellent agreement with the experimental data in terms of IS and CFS in region II; however, PBE-D* 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*.

Zhang, Feng; Hayashi, Michitoshi; Wang, Houng-Wei; Tominaga, Keisuke; Kambara, Ohki; Nishizawa, Jun-ichi; Sasaki, Tetsuo

2014-05-01

212

Scaled Quantum Mechanical scale factors for vibrational calculations using alternate polarized and augmented basis sets with the B3LYP density functional calculation model.  

PubMed

The Scaled Quantum Mechanical (SQM) method of scaling calculated force constants to predict theoretically calculated vibrational frequencies is expanded to include a broad array of polarized and augmented basis sets based on the split valence 6-31G and 6-311G basis sets with the B3LYP density functional. Pulay's original choice of a single polarized 6-31G(d) basis coupled with a B3LYP functional remains the most computationally economical choice for scaled frequency calculations. But it can be improved upon with additional polarization functions and added diffuse functions for complex molecular systems. The new scale factors for the B3LYP density functional and the 6-31G, 6-31G(d), 6-31G(d,p), 6-31G+(d,p), 6-31G++(d,p), 6-311G, 6-311G(d), 6-311G(d,p), 6-311G+(d,p), 6-311G++(d,p), 6-311G(2d,p), 6-311G++(2d,p), 6-311G++(df,p) basis sets are shown. The double d polarized models did not perform as well and the source of the decreased accuracy was investigated. An alternate system of generating internal coordinates that uses the out-of plane wagging coordinate whenever it is possible; makes vibrational assignments via potential energy distributions more meaningful. Automated software to produce SQM scaled vibrational calculations from different molecular orbital packages is presented. PMID:25766474

Legler, C R; Brown, N R; Dunbar, R A; Harness, M D; Nguyen, K; Oyewole, O; Collier, W B

2015-06-15

213

Calculation of vibrational frequencies through a variational reduced-coupling approach.  

PubMed

In this study, we present a new method to perform accurate and efficient vibrational configuration interaction computations for large molecular systems. We use the vibrational self-consistent field (VSCF) method to compute an initial description of the vibrational wave function of the system, combined with the single-to-all approach to compute a sparse potential energy surface at the chosen ab initio level of theory. A Davidson scheme is then used to diagonalize the Hamiltonian matrix built on the VSCF virtual basis. Our method is applied to the computation of the OH-stretch frequency of formic acid and benzoic acid to demonstrate the efficiency and accuracy of this new technique. PMID:17979330

Scribano, Yohann; Benoit, David M

2007-10-28

214

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

215

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

216

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

NASA Astrophysics Data System (ADS)

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.

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.

2015-02-01

217

Reduction of electromagnetic force harmonics in asynchronous traction motor by adapting the rotor slot number  

SciTech Connect

The harmonics in electromagnetic force are source of the mechanical vibration and the audible noise in an asynchronous traction motor. This paper describes an approach to reduce the force harmonics by changing the rotor slot number. Both the radial and tangential forces acting on the stator teeth are calculated by Maxwell stress tenser and their time harmonics are examined by the discrete Fourier decomposition. As a result, the optimal slot number of the rotor to reduce or eliminate the specific force harmonics is determined.

Kim, B.T.; Kwon, B.I.; Park, S.C.

1999-09-01

218

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

219

Time averaging the semiclassical initial value representation for the calculation of vibrational energy levels. II.  

E-print Network

energy levels. II. Application to H2CO, NH3 , CH4, CH2D2 Alexey L. Kaledin and William H. Miller densities of molecules, previously tested successfully on H2O, is applied here to several larger molecules dynamics, however, the phase space average converges more slowly. Results for vibrational energy levels

Miller, William H.

220

Molecular structure and vibrational and chemical shift assignments of 3'-chloro-4-dimethylamino azobenzene by DFT calculations.  

PubMed

In the present work, a combined experimental and theoretical study on ground state molecular structure, spectroscopic and nonlinear optical properties of azo compound 3'-chloro-4-dimethlamino azobenzene are reported. The molecular geometry, vibrational wavenumbers and the first order hyperpolarizability of the title compound were calculated with the help of density functional theory computations. The optimized geometric parameters obtained by using DFT (B3LYP/6-311++G(d,p)) show good agreement with the experimental data. The vibrational transitions were identified based on the recorded FT-IR spectra in the range of 4000-400cm(-1) for solid state. The (1)H isotropic chemical shifts with respect to TMS were also calculated using the gauge independent atomic orbital (GIAO) method and compared with the experimental data. Using the TD-DFT method, electronic absorption spectra of the title compound have been predicted, and good agreement is determined with the experimental ones. To investigate the NLO properties of the title compound, the polarizability and the first hyperpolarizability were calculated using the density functional B3LYP method with the 6-311++G(d,p) basis set. According to results, the title compound exhibits non-zero first hyperpolarizability value revealing second order NLO behavior. In addition, DFT calculations of the title compound, molecular electrostatic potential and frontier molecular orbitals were also performed at 6-311++G(d,p) level of theory. PMID:25468435

Toy, Mehmet; Tanak, Hasan

2014-11-13

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

Conformational and Vibrational Studies of Triclosan  

NASA Astrophysics Data System (ADS)

The conformational equilibrium of triclosan (5-chloro-2-(2, 4-dichlorophenoxy) phenol) have been calculated using density functional theory (DFTe/B3LYP/6-311++G(d, p)) method. Four different geometries were found to correspond to energy minimum conformations. The IR spectrum of triclosan was measured in the 4000-400 cm-1 region. We calculated the harmonic frequencies and intensities of the most stable conformers in order to assist in the assignment of the vibrational bands in the experimental spectrum. The fundamental vibrational modes were characterized depending on their total energy distribution (TED%) using scaled quantum mechanical (SQM) force field method.

Özi?ik, Haci; Bayari, S. Haman; Sa?lam, Semran

2010-01-01

223

Complete pure vibrational spectrum of HD calculated without the Born-Oppenheimer approximation and including relativistic corrections  

SciTech Connect

All 18 bound pure vibrational levels of the HD molecule have been calculated within the framework that does not assume the Born-Oppenheimer (BO) approximation. The nonrelativistic energies of the states have been corrected for the relativistic effects of the order of {alpha}{sup 2} (where {alpha} is the fine structure constant), calculated using the perturbation theory with the nonrelativistic non-BO wave functions being the zero-order approximation. The calculations were performed by expanding the non-BO wave functions in terms of one-center explicitly correlated Gaussian functions multiplied by even powers of the internuclear distance and by performing extensive optimization of the Gaussian nonlinear parameters. Up to 10 000 basis functions were used for each state.

Bubin, Sergiy [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Stanke, Monika [Department of Physics, Nicholas Copernicus University, ul. Grudziadzka 5, PL-87-100 Torun (Poland); Adamowicz, Ludwik [Department of Chemistry, University of Arizona, Tucson, Arizona 85721 (United States); Department of Physics, University of Arizona, Tucson, Arizona 85721 (United States)

2011-04-15

224

Tabulation of hybrid theory calculated e-N2 vibrational and rotational cross sections  

NASA Technical Reports Server (NTRS)

Vibrational excitation cross sections of N2 by electron impact are tabulated. Integrated cross sections are given for transitions v yields v prime where o=or v=or 8 in the energy range 0.1 eV=or E=or 10 eV. The energy grid is chosen to be most dense in the resonance region (2 to 4 eV) so that the substructure is present in the numerical results. Coefficients in the angular distribution formula (differential scattering cross section) for transitions v=0 yields v prime = or 8 are also numerically given over the same grid of energies. Simultaneous rotation-vibration coefficients are also given for transitions v=o,j=o; 1 yields v prime=o, j=o,2,4; 1,3,5. All results are obtained from the hybrid theory.

Chandra, N.; Temkin, A.

1976-01-01

225

CASSCF and CCI calculations of the vibrational band strengths of HCN  

Microsoft Academic Search

HCN has been observed to be a constituent of late type carbon-rich stellar atmospheres and has recently been suggested to be a very important opacity source in cooler carbon stars. The transitions giving rise to the combination vibration-rotation bands in the near infrared region may be expected to be the most important HCN transitions for the structure of the carbon-star

U. G. Jorgensen; J. Almlof; Bengt Gustafsson; Mats Larsson; Per Siegbahn

1985-01-01

226

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

227

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

228

Influence of intramolecular vibrations in third-order, time-domain resonant spectroscopies. II. Numerical calculations  

NASA Astrophysics Data System (ADS)

We model recent experimental wavelength dependent Three Pulse Photon Echo Peak Shift (WD-3PEPS) and Transient Grating (WD-TG) signals considering both solvation dynamics and vibrational contributions. We present numerical simulations of WD-3PEPS and WD-TG signals of two probe molecules: Nile Blue and N,N-bisdimethylphenyl-2,4,6,8-perylenetetracarbonyl diamide to investigate the influence of intramolecular vibrations in the signals. By varying the excitation wavelength, we show that the different initial conditions for the vibrational wave packets significantly affect the signals, especially through the contributions associated with high frequency modes, often neglected in experimental analyses. We show that the temporal properties of both WD-TG and WD-3PEPS signals display sensitivities to both the excitation wavelength and the vibronic structure of the specific probe molecule used. Several mechanisms for generating vibronic modulations in the signals are discussed and their effects on the signals are described. Quantitative agreement between experiment and simulated signals requires accurate characterization of the laser pulses, specifically the magnitude and sign of chirp has a significant effect on the initial temporal properties of the signals. We provide a description of the experimental considerations required for accurate determination of molecular dynamics from 3PEPS and TG experiments and conclude with a brief discussion of the implications of our results for previous analyses of such experiments.

Ohta, Kaoru; Larsen, Delmar S.; Yang, Mino; Fleming, Graham R.

2001-05-01

229

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

230

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

PubMed

We report a rigorous full dimensional quantum dynamics algorithm, the multi-layer Lanczos method, for computing vibrational energies and dipole transition intensities of polyatomic molecules without any dynamics approximation. The multi-layer Lanczos method is developed by using a few advanced techniques including the guided spectral transform Lanczos method, multi-layer Lanczos iteration approach, recursive residue generation method, and dipole-wavefunction contraction. The quantum molecular Hamiltonian at the total angular momentum J = 0 is represented in a set of orthogonal polyspherical coordinates so that the large amplitude motions of vibrations are naturally described. In particular, the algorithm is general and problem-independent. An application is illustrated by calculating the infrared vibrational dipole transition spectrum of CH4 based on the ab initio T8 potential energy surface of Schwenke and Partridge [Spectrochimica Acta, Part A 57, 887 (2001)] and the low-order truncated ab initio dipole moment surfaces of Yurchenko et al. [J. Mol. Spectrosc. 291, 69 (2013)]. A comparison with experiments is made. The algorithm is also applicable for Raman polarizability active spectra. PMID:25637968

Yu, Hua-Gen

2015-01-28

231

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

232

Vibrational spectra, NBO analysis, first order hyperpolarizabilities, thermodynamic functions and NMR chemical shielding anisotropy (CSA) parameters of 5-nitro-2-furoic acid by ab initio HF and DFT calculations  

NASA Astrophysics Data System (ADS)

In this work, FT-IR and FT-Raman spectra are recorded on the solid phase of 5-nitro-2-furoic acid (abbreviated as NFA) in the regions 4000-400 cm-1 and 3500-100 cm-1 respectively. The geometrical parameters, vibrational assignments, HOMO-LUMO energies and NBO calculations are obtained for the monomer and dimer of NFA from HF and DFT (B3LYP) with 6-311++G (d, p) basis set calculations. Second order perturbation energies and electron density (ED) transfer from filled lone pairs of Lewis base to unfilled Lewis acid sites of NFA are discussed on the basis of NBO analysis. Intermolecular hydrogen bonds exist through COOH groups; give the evidence for the formation of dimer entities in the title molecule. The theoretically calculated harmonic frequencies are scaled by common scale factor. The observed and the calculated frequencies are found to be in good agreement. The thermodynamic functions were obtained for the range of temperature 100-1000 K. The polarizability, first hyperpolarizability, anisotropy polarizability invariant has been computed using quantum chemical calculations. The chemical parameters were calculated from the HOMO and LUMO values. The NMR chemical shielding anisotropy (CSA) parameters were also computed for the title molecule.

Balachandran, V.; Rajeswari, S.; Lalitha, S.

2013-09-01

233

Determination of structural and vibrational spectroscopic properties of 2-, 3-, 4-nitrobenzenesulfonamide using FT-IR and FT-Raman experimental techniques and DFT quantum chemical calculations  

NASA Astrophysics Data System (ADS)

In this work, the molecular conformation and vibrational analysis of 2-, 3-, 4-nitrobenzenesulfonamide (abbreviated as 2-, 3-, 4-NBSA) were presented for the ground state using experimental techniques (FT-IR and FT-Raman) and density functional theory (DFT) employing B3LYP exchange correlation with the 6-311++G(d,p) basis set. The complete assignments of fundamental vibrations were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The effects of the nitro group substituent on the characteristic benzene sulfonamides bands in the spectra were discussed. Raman activities calculated by DFT method have been converted to the corresponding Raman intensities using Raman scattering theory. Optimized structure of compounds were interpreted and compared with the earlier reported experimental values for studied molecules. The observed and the calculated geometric parameters and vibrational wavenumbers were compared and found to be in good agreement.

Karabacak, Mehmet; Postalcilar, Emel; Cinar, Mehmet

2012-01-01

234

Molecular structures and vibrational frequencies of xanthine and its methyl derivatives (caffeine and theobromine) by ab initio Hartree-Fock and density functional theory calculations  

NASA Astrophysics Data System (ADS)

The molecular structures, vibrational frequencies and corresponding vibrational assignments of xanthine and its methyl derivatives (caffeine and theobromine) have been calculated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods with 6-31G(d, p) basis set level. The calculations were utilized to the CS symmetries of the molecules. The obtained vibrational frequencies and optimised geometric parameters (bond lengths and bond angles) were seen to be well agreement with the experimental data. The used scale factors which have been obtained the ratio of the frequency values of the strongest peaks in the calculated and experimental spectra seem to cause the gained vibrations well corresponding to the experimental ones. Theoretical infrared intensities and Raman activities are also reported.

Ucun, Fatih; Sa?lam, Adnan; Güçlü, Vesile

2007-06-01

235

A FEM-based method using harmonic overtones to determine the effective elastic, dielectric, and piezoelectric parameters of freely vibrating thick piezoelectric disks.  

PubMed

To gain an understanding of the electroelastic properties of tactile piezoelectric sensors used in the characterization of soft tissue, the frequency-dependent electric impedance response of thick piezoelectric disks has been calculated using finite element modeling. To fit the calculated to the measured response, a new method was developed using harmonic overtones for tuning of the calculated effective elastic, piezoelectric, and dielectric parameters. To validate the results, the impedance responses of 10 piezoelectric disks with diameter-to-thickness ratios of 20, 6, and 2 have been measured from 10 kHz to 5 MHz. A two-dimensional, general purpose finite element partial differential equation solver with adaptive meshing capability run in the frequency-stepped mode, was used. The equations and boundary conditions used by the solver are presented. Calculated and measured impedance responses are presented, and resonance frequencies have been compared in detail. The comparison shows excellent agreement, with average relative differences in frequency of 0.27%, 0.19%, and 0.54% for the samples with diameter-to-thickness ratios of 20, 6, and 2, respectively. The method of tuning the effective elastic, piezoelectric, and dielectric parameters is an important step toward a finite element model that describes the properties of tactile sensors in detail. PMID:23287929

Jonsson, Ulf G; Andersson, Britt M; Lindahl, Olof A

2013-01-01

236

Vibrational Spectroscopy of the G, , ,C Base Pair: Experiment, Harmonic and Anharmonic Calculations, and the Nature of the Anharmonic Couplings  

E-print Network

of amino acid2 and peptide conformations3 and the exploration of nucleic acid base tautomerization in spectroscopic identification of biological conformers and their properties. The structure of nucleic acid ba

de Vries, Mattanjah S.

237

Global Calculations Using Potential Functions and Effective Hamiltonian Models for Vibration-Rotation Spectroscopy and Dynamics of Small Polyatomic Molecules  

NASA Astrophysics Data System (ADS)

It has become increasingly common to use accurate potential energy surfaces and dipole moment surfaces for predictions and assignment of high-resolution vibration-rotation molecular spectra. These surfaces are obtained either from high-level ab initio electronic structure calculations or from a direct fit to experimental spectroscopic data. The talk will continue a discussion of some recent advances in the domain of the "potentiology". The role of basis extrapolations, of the Born-Oppenheimer breakdown corrections , in particular for very highly excited vibration states will be considered. As effective polyad Hamiltonians and band transition moment operators are still widely used for data reductions in high-resolutions molecular spectroscopy, experimental spectra analyses invoke a need for accurate methods of building physically meaningful effective models from ab initio surfaces. This involves predictions for various spectroscopic constants, including vibration dependence of rotational and centrifugal distortion and resonance coupling parameters. Topics planned for discussion include: high-order Contact Transformations of rovibrational Hamiltonians and of the dipole moment for small polyatomic molecules; convergence issues; the role of the anharmonicity in a potential energy function and of resonance couplings on the normal mode mixing and on vib-rot assignments with application to high energy vibration levels of SO_2 and to ozone near the dissociation limit; intensity anomalies in H_2S / HDS / D_2S spectra, relation of the shape of ab initio dipole moment surfaces with a "mystery" of nearly vanishing symmetry allowed bands. A full account for symmetry properties requires efficient theoretical tools for transformations of molecular Hamiltonians such as irreducible tensor formalism, applications using phosphine and methane potentials will be discussed. Both potential functions and effective polyad Hamiltonians allow studying changes in quasi-classical vibration periodic orbits and in of the nodal structure of wavefunctions with mass variations. An investigation of the consequences of symmetry breaking by isotopic substitution, in the classical and quantum dynamics is particularly instructive. This helps understanding the fingerprints of bifurcations effects in the quantum states of isotopologues and their assignment. The work of our research team with collaborators in these areas will be described.

Tuyterev, Vladimir

2010-06-01

238

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

239

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

240

Vibrational Properties of Hexagonal Boron Nitride: Inelastic X-Ray Scattering and Ab Initio Calculations  

SciTech Connect

The phonon dispersion relations of bulk hexagonal boron nitride have been determined from inelastic x-ray scattering measurements and analyzed by ab initio calculations. Experimental data and calculations show an outstanding agreement and reconcile the controversies raised by recent experimental data obtained by electron-energy loss spectroscopy and second-order Raman scattering.

Serrano, J.; Bosak, A.; Krisch, M. [European Synchrotron Radiation Facility, Boite Postale 220, 38043 Grenoble (France); Arenal, R. [Materials Sciences Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Watanabe, K.; Taniguchi, T.; Kanda, H. [National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044 (Japan); Rubio, A. [Departamento de Fisica de Materiales, Facultad de Ciencias Quimicas, Universidad del Pais Vasco, Centro Mixto CSIC-UPV/EHU and Donostia International Physics Center, E-20018 San Sebastian, Basque Country (Spain); European Theoretical Spectroscopy Facility (ETSF), E-20018 San Sebastian, Basque Country (Spain); Wirtz, L. [IEMN - CNRS-UMR 8520, Boite Postale 60069, 59652 Villeneuve dAscq Cedex (France); European Theoretical Spectroscopy Facility - ETSF, E-20018 San Sebastian, Basque Country (Spain)

2007-03-02

241

Vibrations of rings with circular cross section  

Microsoft Academic Search

Conclusions 1.Rotary inertia and shear have a substantial effect on the vibrations of a ring, both in the plane of its curvature and outside it. This effect is particularly great at the higher harmonics.2.The effect of tensile strain on the pure bending vibrations is slight and is notic eable only with the lower harmonics. In the higher harmonics, tension does

V. B. Zhukov

1978-01-01

242

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

243

HO2 ro-vibrational bound-state calculations for large angular momentum: J = 30, 40, and 50.  

PubMed

The Lanczos homogeneous filter diagonalization method and the real Chebyshev filter diagonalization scheme incorporating doubling of the autocorrelation functions have been employed to compute the HO2 ro-vibrational states for high total angular momenta, J = 30, 40, and 50. For such computationally challenging calculations, we have adopted a parallel computing strategy to perform the matrix-vector multiplications. Low-lying bound states and high-lying bound states close to the dissociation threshold are reported. For low-lying bound states, a spectroscopic assignment has been attempted and the widely used approximate J-shifting method has been tested for this deep-well system. For high-lying bound states, the attempted spectroscopic assignments as well as the J-shifting approximation fail because of very strong Coriolis mixing, indicating that the Coriolis couplings are important for this system. PMID:16509649

Zhang, Hong; Smith, Sean C

2006-03-01

244

The absolute structures of separated PCB-methylsulfone enantiomers determined by vibrational circular dichroism and quantum chemical calculations  

Microsoft Academic Search

Four chiral transformation products of polychlorinated biphenyls (PCBs), the most prevalent methylsulfonyl-PCBs (MeSO2-PCBs) 3-MeSO2-2,2?,4?,5,5?,6-hexachlorobiphenyl (3-149), 3-MeSO2-2,2?,3?,4?,5,5?,6-heptachlorobiphenyl (3-174), 3-MeSO2-2,2?,3?,4?,5,6-hexachlorobiphenyl (3-132), and 4-MeSO4-2,2?,3,3?,4?,6-hexachlorobiphenyl (4-132), were separated into their enantiomers, in order to determine the absolute configuration of these enantiomers using vibrational circular dichroism (VCD) complemented by quantum chemical ab initio calculations (QC). In all four derivatives, the angles between the planes of

Jens Döbler; Nils Peters; Christina Larsson; Åke Bergman; Ekkehard Geidel; Heinrich Hühnerfuss

2002-01-01

245

Beam bending-torsion dynamic stiffness method for calculation of exact vibration modes  

Microsoft Academic Search

The exact dynamic stiffness matrix is derived for a straight and uniform beam element whose elastic and inertial axes are not coincident. Elementary bending-torsion beam theory is used, and bending translation is restricted to one direction. The element matrix can be used in the dynamic stiffness method for calculation of exact natural frequencies, mode shapes, and generalized masses for planar

W. L. Hallauer; R. Y. L. Liu

1982-01-01

246

A low-storage filter-diagonalization method to calculate expectation values of operators non-commutative with the Hamiltonian: Vibrational assignment of HOCl  

NASA Astrophysics Data System (ADS)

A method based on the Hellmann-Feynman theorem is proposed for calculating expectation values of operators non-commutative with the system Hamiltonian, ?0. It is applicable in both the low-storage filter-diagonalization (LSFD) and Lanczos methods. Specifically, LSFD is used to determine eigenvalues of ?0 and a perturbed Hamiltonian consisting of ?0 and the non-commutative operator ?': ??= ?0+ ??'. The difference between the two spectra yields the expectation values of ?' without explicit calculating the eigenstates. For an appropriate choice of ?', information about vibrational assignments can be obtained. As an example, the vibrational assignment of HOCl and its Fermi resonances are analyzed.

Chen, Rongqing; Guo, Hua

1999-07-01

247

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

248

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

249

Calculation of the transitions in the amine inversion vibration of some local anesthetics  

NASA Astrophysics Data System (ADS)

In the para-amino group of the local anesthetics benzocaine, procaine and procaine hydrochloride, the potential function of inversion, the barrier height V? i and the optimum ? o inversion angle have been determinated. Two methods are shown for calculating transitions based on the two frequencies of inversion which easily can be detected in the infrared absorption and Raman spectra in solid compounds. Also the frequencies associated with tra nsitions are able to be obtained.

Alcolea Palafox, M.

1988-05-01

250

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

251

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

252

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

253

Study of molecular structure, vibrational, electronic and NMR spectra of oncocalyxone A using DFT and quantum chemical calculations.  

PubMed

Oncocalyxone A (C17H18O5) is the major secondary metabolite isolated from ethanol extract from the heartwood of Auxemma oncocalyx Taub popularly known as "pau branco". Oncocalyxone A (Onco A) has many pharmaceutical uses such as: antitumor, analgesic, antioxidant and causative of inhibition of platelet activation. We have performed the optimized geometry, total energy, conformational study, molecular electrostatic potential mapping, frontier orbital energy gap and vibrational frequencies of Onco A employing ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method with 6-311++G(d,p) basis set. Stability of the molecule arising from hyperconjugative interactions and/or charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV-vis spectrum of the compound was recorded in DMSO and MeOH solvent. The TD-DFT calculations have been performed to explore the influence of electronic absorption spectra in the gas phase, as well as in solution environment using IEF-PCM and 6-31G basis set. The (13)C NMR chemical shifts have been calculated with the B3LYP/6-311++G(d,p) basis set and compared with the experimental values. These methods have been used as tools for structural characterization of Onco A. PMID:23747376

Joshi, Bhawani Datt; Srivastava, Anubha; Honorato, Sara Braga; Tandon, Poonam; Pessoa, Otília Deusdênia Loiola; Fechine, Pierre Basílio Almeida; Ayala, Alejandro Pedro

2013-09-01

254

Study of molecular structure, vibrational, electronic and NMR spectra of oncocalyxone A using DFT and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

Oncocalyxone A (C17H18O5) is the major secondary metabolite isolated from ethanol extract from the heartwood of Auxemma oncocalyx Taub popularly known as “pau branco”. Oncocalyxone A (Onco A) has many pharmaceutical uses such as: antitumor, analgesic, antioxidant and causative of inhibition of platelet activation. We have performed the optimized geometry, total energy, conformational study, molecular electrostatic potential mapping, frontier orbital energy gap and vibrational frequencies of Onco A employing ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method with 6-311++G(d, p) basis set. Stability of the molecule arising from hyperconjugative interactions and/or charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV-vis spectrum of the compound was recorded in DMSO and MeOH solvent. The TD-DFT calculations have been performed to explore the influence of electronic absorption spectra in the gas phase, as well as in solution environment using IEF-PCM and 6-31G basis set. The 13C NMR chemical shifts have been calculated with the B3LYP/6-311++G(d, p) basis set and compared with the experimental values. These methods have been used as tools for structural characterization of Onco A.

Joshi, Bhawani Datt; Srivastava, Anubha; Honorato, Sara Braga; Tandon, Poonam; Pessoa, Otília Deusdênia Loiola; Fechine, Pierre Basílio Almeida; Ayala, Alejandro Pedro

2013-09-01

255

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

E-print Network

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 CH$_3$CN (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 $8 \\times 10^{11}$ GB. With the approach of this paper only 1 GB of memory is necessary. Results for CH$_3$CN agree well with those of a previous calculation on the same potential.

Arnaud Leclerc; Tucker Carrington

2014-05-12

256

Vibrational spectroscopic studies and DFT calculations on tribromoacetate and tribromoacetic acid in aqueous solution  

NASA Astrophysics Data System (ADS)

Aqueous solutions of sodium tribromoacetate (NaCBr 3CO 2) and its corresponding acid (CBr 3COOH) have been studied using Raman and infrared spectroscopy. The spectra of the species in solution were assigned according to symmetry C s. Characteristic bands of CBr 3CO 2-(aq) and the tribromoacetic acid, CBr 3COOH(aq), are discussed. For the hydrated anion, the CO 2 group, the symmetric CO 2 stretching mode at 1332 cm -1 and the asymmetric stretching mode at 1651 cm -1 are characteristic while the C dbnd O mode at 1730 cm -1 is characteristic for the spectra of the acid. The stretching mode, ?C-C at 912 cm -1 for CBr 3CO 2-(aq) is 10 cm -1 lower in the anion compared with that of the acid. These characteristic modes are compared to those in acetate, CH 3CO 2-(aq). Coupling of the modes are fairly extensive and therefore DFT calculations have been carried out in order to compare the measured spectra with the calculated ones. The geometrical parameters such as bond length and bond angles of the tribromoacetate, and tribromoacetic acid have been obtained and may be compared with the ones published for other acetates and their conjugated acids. CBr 3COOH(aq) is a moderately strong acid and the p Ka value derived from quantitative Raman measurements is equal to -0.23 at 23 °C. The deuterated acid CBr 3COOD in heavy water has been measured as well and the assignments were given.

Rudolph, Wolfram W.; Irmer, Gert

2011-09-01

257

SUR LE COMMUTATEUR DE DEUX POLYNOMES HOMOGNES. APPLICATION AU CALCUL DE L'NERGIE DE VIBRATION D'UNE MOLCULE POLYATOMIQUE  

E-print Network

'une molécule polyatomique suivant la méthode de H. H. Nielsen. LE JOURNAL DE PHYSIQUE ET LE RADIUM. TOME 16] apparaît lorsqu'on calcule l'énergie de vibration d'une molécule poly- atomique, en utilisant la méthode de

Paris-Sud XI, Université de

258

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

259

The Two-Degree-of-Freedom Tuned-Mass Damper for Suppression of Single-Mode Vibration Under Random and Harmonic Excitation  

Microsoft Academic Search

Whenever a tuned-mass damper is attached to a primary system, motion of the absorber body in more than one degree of freedom (DOF) relative to the primary system can be used to attenuate vibration of the primary system. In this paper, we propose that more than one mode of vibration of an absorber body relative to a primary system be

Lei Zuo; Samir A. Nayfeh

2006-01-01

260

Ab initio calculations of force fields for H 2CN and C1HCN and vibrational energies of H 2CN  

NASA Astrophysics Data System (ADS)

Ab initio calculations of electronic energies and fitted force fields are reported for H 2CN and C1HCN. The force field for H 2CN in internal coordinates is used in rigorous, full dimensional variational calculations of numerous vibrational states. The same force field is also used in vibrational self-consistent field (VSCF) calculations, using a new code which is currently restricted to at most four-mode coupling. The convergence of VSCF energies in internal coordinates is examined for one-mode, two-mode, three-mode, and four-mode approximations to the full internal coordinate force field. VSCF calculations using a conventional normal coordinate force field for H 2CN are also reported.

Carter, Stuart; Bowman, Joel M.; Harding, Lawrence B.

1997-07-01

261

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

262

Ab Initio Calculation Of Vibrational Frequencies In AsxS1-x Glass And The Raman Spectra  

NASA Astrophysics Data System (ADS)

We have made many different models for the understanding of the structure of AsS glass. In particular, we made the models of AsS3 (triangular), AsS3 (pyramid), AsS4 (3S on one side, one on the other side of As, S3-As-S), AsS4 (pyramid), AsS4 (tetrahedral), AsS7, As2S6 (dumb bell), As2S3 (bipyramid), As2S3 (zig-zag), As3S2 (bipyramid), As3S2 (linear), As4S4 (cubic), As4S4 (ring), As4S (tetrahedral), As4S (pyramid), As4S3 (linear) and As6S2 (dumb bell) by using the density functional theory which solves the Schrödinger equation for the given number of atoms in a cluster in the local density approximation. The models are optimized for the minimum energy which determines the structures, bond lengths and angles. For the optimized clusters, we calculated the vibrational frequencies in each case by calculating the gradients of the first principles potential. We compare the experimentally observed Raman frequencies with those calculated so that we can identify whether the cluster is present in the glass. In this way we find that AsS4 (S3-As-S), As4S4 (ring), As2S3 (bipyramid), As4S4 (cubic), As4S3 (linear), As2S3 (zig-zag), AsS4 (Td), As2S6 (dumb bell), AsS3 (triangle) and AsS3 (pyramid) structures are present in the actual glass.

Rosli, Ahmad Nazrul; Kassim, Hasan Abu; Shrivastava, Keshav N.

2009-06-01

263

Isomers and conformers of two push pull hydrazines studied by NMR and vibrational spectroscopy and by ab initio calculations  

NASA Astrophysics Data System (ADS)

The isomers and conformers of two push-pull hydrazines: 3- N, N-dimethylhydrazino-2-acetyl propenenitrile [(H 3C) 2N sbnd NH sbnd CH dbnd C(CN)(COCH 3)] (DMHAP) and 3- N, N-dimethylhydrazino-2-methylsulfonyl propenenitrile [(H 3C) 2N sbnd NH sbnd CH dbnd C(CN)(SO 2CH 3)] (DMHSP) have been studied experimentally by NMR and vibrational spectroscopy and theoretically by the ab initio calculations at MP2 level in 6-31G** basis set. The IR and Raman spectra of both compounds as a solid and solute in various solvents have been recorded. The NMR spectra were obtained in chloroform and DMSO at room temperature. Both compounds have been prepared by the same way. NMR spectra revealed that DMHAP was prepared as a pure Z-isomer whereas in the case of DMHSP a pure E-isomer was obtained. Due to the low barrier for both compounds practically free isomerisation process occurred in the solutions but in opposite directions. Whereas DMHAP exists in the solid state and in the less polar solvent as Z-isomer, in more polar solvents the appearance of next two conformers of E-isomer was observed. On the contrary DMHSP exists in the solid state and in the more polar solvent as E-isomer only but in less polar solvent the presence of Z-isomer was observed as well. Conformational possibilities of both studied compounds are given by the rotation of dimethylhydrazino group with its anti- or syn-orientation towards the olefinic double bond. Moreover, by the rotation of the acetyl group with Z- and E-orientation of carbonyl bond towards olefinic double bond can occur in DMHAP. Vibrational and NMR spectra revealed the existence of single conformer with intramolecular hydrogen bond for Z-isomer in less polar solvent and next two conformers for E-isomer of DMHAP with Z-orientation of acetyl group and anti and syn orientation of dimethylhydrazine group in more polar solvents. For E-isomer of DMHSP two conformers with anti or syn orientations of dimethylhydrazino group have been also confirmed by NMR spectra in more polar solvents. Additionally the third DMHSP conformer with anti orientation of dimethylhydrazino group originating from Z-isomer was detected in less polar solvents. These experimental findings have been supported by ab initio calculations with solvent effect inclusion.

Gróf, M.; Polovková, J.; Gatial, A.; Milata, V.; ?ernuchová, P.; Prónayová, N.; Mat?jka, P.

2007-05-01

264

Ab initio structures and vibrational analysis of the isoprene conformers  

NASA Astrophysics Data System (ADS)

Complete gradient optimizations of the structures and the calculation of the harmonic force fields of the s- trans( anti) and gauche conformers of isoprene (2-methylbuta-1,3-diene) are reported at the RHF/6-31G level. The dihedral angle of the gauche conformer is found to be 41.0° from the planar s- cis( syn) form. The force fields obtained are refined using scale factors transferred from analogous calculations for trans-butadiene-1,3 and ethane. The direct vibrational problems are solved for both conformers of isoprene. A complete assignment of the experimental vibrational frequencies is given.

Bock, Ch. W.; Panchenko, Yu. N.; Krasnoshchiokov, S. V.; Aroca, R.

1987-09-01

265

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

266

Normal coordinate analysis and vibrational spectra of 9-?-D-arabinofuranosyladenine hydrochloride (ara-A.HCl)  

Microsoft Academic Search

The vibrational spectra of a synthetic purine nucleoside with known antiviral activity, 9-ß-D-arabino-furanosyladenine hydrochloride (ara-A.HCl) are reported. The Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectra were recorded in the 4000-30 cm-1 spectral region. The harmonic frequencies and potential energy distributions (PED) of the vibrational modes of ara-A.HCI were calculated by two different methods: a classical molecular mechanics

L. E. Bailey; A. Hernanz; R. Navarro; T. Theophanides

1996-01-01

267

Anharmonic vibrational frequency calculations of 5,6-dihydrouracil and its complex with water: testing improved semiempirical potentials for biological molecules  

NASA Astrophysics Data System (ADS)

The anharmonic vibrational spectra of the mutant nucleobase 5,6 dihydrouracil (DHU) and its complex with water are computed and the results are analysed with focus on the properties of the anharmonic coupling between different modes. A recently proposed potential surface is used, based on improving the potential from semiempirical PM3 electronic structure theory. This improved potential energy surface is obtained by a coordinate scaling that yields agreement for harmonic frequencies obtained through ab initio (MP2) or DFT methods. The improved PM3 potentials implemented herein give anharmonic frequencies that are in good agreement with experiment for isolated DHU. Similarly anharmonic frequencies for the DHU-water complex give good agreement when compared to experiments carried out on a remarkably similar model system; uracil-water. This supports the use of the improved PM3 potentials for the spectrochemical description of nucleobases and related molecules. The anharmonic frequencies for the scaled PM3 potential are computed by the vibrational self-consistent field (VSCF) method. The anharmonic coupling interaction between different vibrational modes are analyzed and characterized. For example, the CO out of plane bending mode in isolated DHU was observed to couple most strongly with the NH stretch mode at 3478 cm-1. In the case of the DHU-H2O complex, strong coupling was observed between the O-3H water stretch and the CO out of plane bending modes of DHU at 759 cm-1. The results suggest insights into patterns of intramolecular vibrational energy transfer in DHU and DHU-H2O.

Adesokan, Adeyemi A.; Fredj, Erick; Brown, Eric C.; Gerber, R. Benny

268

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

269

Vibrational dynamics of rutile-type GeO2 from micro-Raman spectroscopy experiments and first-principles calculations  

NASA Astrophysics Data System (ADS)

The vibrational dynamics of germanium dioxide in the rutile structure has been investigated by using polarized micro-Raman scattering spectroscopy coupled with first-principles calculations. Raman spectra were carried out in backscattering geometry at room temperature from micro-crystalline samples either unoriented or oriented by means of a micromanipulator, which enabled successful detection and identification of all the Raman active modes expected on the basis of the group theory. In particular, the Eg mode, incorrectly assigned or not detected in the literature, has been definitively observed by us and unambiguously identified at 525 \\text{cm}-1 under excitation by certain laser lines, thus revealing an unusual resonance phenomenon. First-principles calculations within the framework of the density functional theory allow quantifying both wave number and intensity of the Raman vibrational spectra. The excellent agreement between calculated and experimental data corroborates the reliability of our findings.

Sanson, A.; Pokrovski, G. S.; Giarola, M.; Mariotto, G.

2015-01-01

270

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

271

Theoretical investigation of highly excited vibrational states in DFCO: Calculation of the out-of-plane bending states and simulation of the intramolecular vibrational energy redistribution  

NASA Astrophysics Data System (ADS)

A previously developed modified Davidson scheme [C. Iung and F. Ribeiro, J. Chem. Phys. 121, 174105 (2005)] is applied to compute and analyze highly excited (?2,?6) eigenstates in DFCO. The present paper is also devoted to the simulations of the intramolecular vibrational energy redistribution (IVR) initiated by an excitation of the out-of-plane bending vibration (n?6, n =2,4,6,…,18, and 20). The multiconfiguration time-dependent Hartree method is exploited to propagate the corresponding six-dimensional wave packets. A comprehensive comparison with experimental data as well as with previous simulations of IVR in HFCO [G. Pasin et al. J. Chem. Phys. 124, 194304 (2006)] is presented.

Pasin, Gauthier; Iung, Christophe; Gatti, Fabien; Meyer, Hans-Dieter

2007-01-01

272

Quantum mechanical calculations of vibrational population inversion in chemical reactions - Numerically exact L-squared-amplitude-density study of the H2Br reactive system  

NASA Technical Reports Server (NTRS)

Numerically exact, fully three-dimensional quantum mechanicl reactive scattering calculations are reported for the H2Br system. Both the exchange (H + H-prime Br to H-prime + HBr) and abstraction (H + HBR to H2 + Br) reaction channels are included in the calculations. The present results are the first completely converged three-dimensional quantum calculations for a system involving a highly exoergic reaction channel (the abstraction process). It is found that the production of vibrationally hot H2 in the abstraction reaction, and hence the extent of population inversion in the products, is a sensitive function of initial HBr rotational state and collision energy.

Zhang, Y. C.; Zhang, J. Z. H.; Kouri, D. J.; Haug, K.; Schwenke, D. W.

1988-01-01

273

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

274

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

275

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

276

Accurate non-Born-Oppenheimer calculations of the complete pure vibrational spectrum of ditritium using all-particle explicitly correlated Gaussian functions  

NASA Astrophysics Data System (ADS)

Very accurate variational calculations of the complete pure vibrational spectrum of the ditritium (T2) molecule are performed within the framework where the Born-Oppenheimer approximation is not assumed. After separating out the center-of-mass motion from the total laboratory-frame Hamiltonian, T2 becomes a three-particle problem. States corresponding to the zero total angular momentum, which are pure vibrational states, are spherically symmetric in this framework. The wave functions of these states are expanded in terms of all-particle, one-center, spherically symmetric explicitly correlated Gaussian functions multiplied by even non-negative powers of the internuclear distance. In the calculations the total energies, the dissociation energies, and expectation values of some operators dependent on interparticle distances are determined.

Bubin, Sergiy; Stanke, Monika; Adamowicz, Ludwik

2014-04-01

277

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

NASA Astrophysics Data System (ADS)

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.

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

2011-11-01

278

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

279

Full-dimensional multi configuration time dependent Hartree calculations of the ground and vibrationally excited states of He2,3Br2 clusters  

NASA Astrophysics Data System (ADS)

Quantum dynamics calculations are reported for the tetra-, and penta-atomic van der Waals HeNBr2 complexes using the multiconfiguration time-dependent Hartree (MCTDH) method. The computations are carried out in satellite coordinates, and the kinetic energy operator in this set of coordinates is given. A scheme for the representation of the potential energy surface based on the sum of the three-body HeBr2 interactions at CSSD(T) level plus the He-He interaction is employed. The potential surfaces show multiple close lying minima, and a quantum description of such highly floppy multiminima systems is presented. Benchmark, full-dimensional converged results on ground vibrational/zero-point energies are reported and compared with recent experimental data available for all these complexes, as well as with previous variational quantum calculations for the smaller HeBr2 and He2Br2 complexes on the same surface. Some low-lying vibrationally excited eigenstates are also computed by block improved relaxation calculations. The binding energies and the corresponding vibrationally averaged structures are determined for different conformers of these complexes. Their relative stability is discussed, and contributes to evaluate the importance of the multiple-minima topology of the underlying potential surface.

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

2011-08-01

280

Molecular structure, vibrational spectra, HOMO, LUMO and NMR studies of 2,3,4,5,6-Penta Bromo Toluene and Bromo Durene based on density functional calculations  

NASA Astrophysics Data System (ADS)

This work deals with the vibrational spectra of 2,3,4,5,6-Penta Bromo Toluene (PBT) and Bromo Durene (BD) by quantum chemical calculations. The solid phase FTIR and FT-Raman spectra of the title compounds were recorded in the regions 4000-400 cm-1 and 4000-50 cm-1, respectively. The spectra were interpreted with the aid of normal coordinate analysis based on density functional theory (DFT) using B3LYP/6-31G? level and basis set combinations and was scaled using various scale factors yielding a good agreement between observed and calculated frequencies. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. The HOMO and LUMO energies were calculated within the molecule. 13C and 1H NMR chemical shifts results were also calculated and compared with the experimental values. Thermodynamical properties like entropy heat capacity, zero point energy have been calculated for the title molecules.

Krishna Kumar, V.; Suganya, S.; Mathammal, R.

281

Vibrational frequency analysis, FT-IR, FT-Raman, ab initio, HF and DFT studies, NBO, HOMO-LUMO and electronic structure calculations on pycolinaldehyde oxime.  

PubMed

In this work, the vibrational spectral analysis is carried out by using Raman and infrared spectroscopy in the range 100-4000 cm(-1)and 50-4000 cm(-1), respectively, for pycolinaldehyde oxime (PAO) (C6H6N2O) molecule. The vibrational frequencies have been calculated and scaled values are compared with experimental FT-IR and FT-Raman spectra. The structure optimizations and normal coordinate force field calculations are based on HF and B3LYP methods with 6-311++G(d,p) basis set. The results of the calculation shows excellent agreement between experimental and calculated frequencies in B3LYP/6-311++G(d,p) basis set. The optimized geometric parameters are compared with experimental values of PAO. The non linear optical properties, NBO analysis, thermodynamics properties and mulliken charges of the title molecule are also calculated and interpreted. A study on the electronic properties, such as HOMO and LUMO energies, are performed by time-dependent DFT (TD-DFT) approach. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) are performed. The effects due to the substitutions of CH=NOH ring are investigated. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule are calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. PMID:23994677

Suvitha, A; Periandy, S; Boomadevi, S; Govindarajan, M

2014-01-01

282

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

283

Vibrational frequencies of the ground and lowest excited triplet state of thioformaldehyde h2, d2, and hd  

NASA Astrophysics Data System (ADS)

Harmonic vibrational frequencies calculated by ab initio methods with double zeta plus polarization basis sets are reported for the ? and ? states of H2CS, D2CS, and HDCS. These frequencies are scaled to predict as yet unknown experimental values. For the triplet state, vibrational energy levels are given for a double minimum potential in the out-of-plane bending coordinate within a rigid bender approximation.

Goddard, J. D.; Clouthier, D. J.

1982-05-01

284

FT-IR and FT-Raman, vibrational assignments, molecular geometry, ab initio (HF) and DFT (B3LYP) calculations for 1,3-dichlorobenzene  

NASA Astrophysics Data System (ADS)

The FT-IR and FT-Raman vibrational spectra of 1,3-dichlorobenzene (1,3-DCB) have been recorded using Bruker IFS 66 V Spectrometer in the range 4000-100 cm -1. A detailed vibrational spectral analysis has been carried out and assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The optimized molecular geometry, vibrational frequencies, atomic charges, dipole moment, rotational constants and several thermodynamic parameters in the ground state were calculated using ab initio Hartree-Fock (HF) and DFT (B3LYP) methods with 6-31++G (d, p) and 6-311++G (d, p) basis sets. With the help of different scaling factors, the observed vibrational wave numbers in FT-IR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wave numbers in the expected range. The inductive effect of Chlorine atoms in the benzene molecule has also been investigated.

Mahadevan, D.; Periandy, S.; Ramalingam, S.

2011-09-01

285

The vibrational spectrum of (H 2O) 2: comparison between anharmonic ab initio calculations and neon matrix infrared data between 9000 and 90 cm -1  

NASA Astrophysics Data System (ADS)

From the spectrum of water (H 216O and H 218O) trapped in neon matrix recorded between 50 and 9000 cm -1 29 vibrational transitions from the ground state have been identified for the water dimer. Twenty measured in the mid- and near infrared have been assigned to one-, two- and three-quanta transitions of the intramolecular modes, five in the far infrared to intermolecular modes and four in the mid infrared to binary intra + inter combinations. These assignments are based on 16O/ 18O isotopic shifts and on the comparison with the spectrum of the acetonitrile:water one to one complex in which the vibrational properties of the water subunit are very close to that of the proton donor molecule in (H 2O) 2. The comparison of the results in the mid- and far infrared with those obtained in the gas phase shows that the Ne matrix induced perturbations are very small for the intramolecular vibrations and do not exceed 20% for the intermolecular ones. Accordingly this set of data can be used to test the ability for a new version of the Gaussian program to account for the anharmonicity of vibrations and its evolution upon hydrogen-bonding. The results show that the anharmonicity coefficients are generally well reproduced for the intramolecular modes and that the highly anharmonic low frequency intermolecular modes are calculated less than 20% higher than observed in the gas phase.

Bouteiller, Y.; Perchard, J. P.

2004-10-01

286

Emission spectroscopy, harmonic vibrational frequencies, and improved ground state structures of jet-cooled monochloro- and monobromosilylene (HSiCl and HSiBr)  

Microsoft Academic Search

The ground state harmonic frequencies of gas phase H\\/DSi35Cl and H\\/DSi79Br have been determined by exciting single vibronic bands of the A~ 1A''-X~ 1A' electronic transition and recording the dispersed fluorescence. The jet-cooled radicals were produced in a pulsed discharge jet using H\\/DSiX3 (X=Cl or Br) precursors. The emission data were fitted to an anharmonic model and a normal coordinate

David A. Hostutler; Nicholas Ndiege; Dennis J. Clouthier; Steven W. Pauls

2001-01-01

287

Anomalous isotopic effect on vibrational properties of HXeOH  

NASA Astrophysics Data System (ADS)

We study IR absorption spectra of various isotopomers of the HXeOH molecules isolated in solid Xe at 7 K. Upon the 16O to 18O isotopic substitution, we found experimentally an anomalous shift of the H-Xe stretching vibration frequency of HXeOD and HXeOH. This spectral behavior, when the fundamental frequency shifts up in energy for the heavier oxygen isotope, cannot be understood on the basis of the harmonic approximation for fundamental vibrations, and the anharmonic coupling between normal modes is presumably responsible for this anomalous effect. Our anharmonic CC-VSCF calculations describe correctly the experimental observations.

Khriachtchev, Leonid; Lundell, Jan; Pettersson, Mika; Tanskanen, Hanna; Räsänen, Markku

2002-03-01

288

MULTIMODE quantum calculations of vibrational energies and IR spectrum of the NO{sup +}(H{sub 2}O) cluster using accurate potential energy and dipole moment surfaces  

SciTech Connect

A new, full (nine)-dimensional potential energy surface and dipole moment surface to describe the NO{sup +}(H{sub 2}O) cluster is reported. The PES is based on fitting of roughly 32?000 CCSD(T)-F12/aug-cc-pVTZ electronic energies. The surface is a linear least-squares fit using a permutationally invariant basis with Morse-type variables. The PES is used in a Diffusion Monte Carlo study of the zero-point energy and wavefunction of the NO{sup +}(H{sub 2}O) and NO{sup +}(D{sub 2}O) complexes. Using the calculated ZPE the dissociation energies of the clusters are reported. Vibrational configuration interaction calculations of NO{sup +}(H{sub 2}O) and NO{sup +}(D{sub 2}O) using the MULTIMODE program are performed. The fundamental, a number of overtone, and combination states of the clusters are reported. The IR spectrum of the NO{sup +}(H{sub 2}O) cluster is calculated using 4, 5, 7, and 8 modes VSCF/CI calculations. The anharmonic, coupled vibrational calculations, and IR spectrum show very good agreement with experiment. Mode coupling of the water “antisymmetric” stretching mode with the low-frequency intermolecular modes results in intensity borrowing.

Homayoon, Zahra, E-mail: zhomayo@emory.edu [Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322 (United States)

2014-09-28

289

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

290

MULTIMODE quantum calculations of vibrational energies and IR spectrum of the NO?(H?O) cluster using accurate potential energy and dipole moment surfaces.  

PubMed

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. PMID:25273441

Homayoon, Zahra

2014-09-28

291

Quasiclassical trajectory calculations for Li(2(2)P(J)) + H2 ? LiH(X(1)?+) + H: influence by vibrational excitation and translational energy.  

PubMed

Ab initio potential energy surfaces and the corresponding analytical energy functions of the ground 1A' and excited 2A' states for the Li(2(2)P) plus H(2) reaction are constructed. Quasiclassical trajectory calculations on the fitted energy functions are performed to characterize the reactions of Li(2(2)P) with H(2)(v = 0, j = 1) and H(2)(v = 1, j = 1) as well as the reaction when the vibrational energy is replaced by collision energy. For simplicity, the transition probability is assumed to be unity when the trajectories go through the crossing seam region and change to the lower surface. The calculated rotational distributions of LiH(v = 0) for both H(2)(v = 0, j = 1) and H(2)(v = 1, j = 1) reactions are single-peaked with the maximum population at j' = 7, consistent with the previous observation. The vibrational excitation of H(2)(v = 1) may enhance the reaction cross section of LiH(v' = 0) by about 200 times, as compared to a result of 93-107 reported in the experimental measurements. In contrast, the enhancement is 3.1, if the same amount of energy is deposited in the translational states. This endothermic reaction can be considered as an analog of late barrier. According to the trajectory analysis, the vibrational excitation enlarges the H-H distance in the entrance channel to facilitate the reaction, but the excess energy may not open up additional reaction configuration. PMID:21261342

Hsiao, Ming-Kai; Lin, King-Chuen; Hung, Yu-Ming

2011-01-21

292

Strong second harmonic generation in SiC, ZnO, GaN two-dimensional hexagonal crystals from first-principles many-body calculations.  

PubMed

The second harmonic generation (SHG) intensity spectrum of SiC, ZnO, GaN two-dimensional hexagonal crystals is calculated by using a real-time first-principles approach based on Green's function theory [Attaccalite et al., Phys. Rev. B: Condens. Matter Mater. Phys. 2013 88, 235113]. This approach allows one to go beyond the independent particle description used in standard first-principles nonlinear optics calculations by including quasiparticle corrections (by means of the GW approximation), crystal local field effects and excitonic effects. Our results show that the SHG spectra obtained using the latter approach differ significantly from their independent particle counterparts. In particular they show strong excitonic resonances at which the SHG intensity is about two times stronger than within the independent particle approximation. All the systems studied (whose stabilities have been predicted theoretically) are transparent and at the same time exhibit a remarkable SHG intensity in the range of frequencies at which Ti:sapphire and Nd:YAG lasers operate; thus they can be of interest for nanoscale nonlinear frequency conversion devices. Specifically the SHG intensity at 800 nm (1.55 eV) ranges from about 40-80 pm V(-1) in ZnO and GaN to 0.6 nm V(-1) in SiC. The latter value in particular is 1 order of magnitude larger than values in standard nonlinear crystals. PMID:25766901

Attaccalite, C; Nguer, A; Cannuccia, E; Grüning, M

2015-04-14

293

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

PubMed

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. PMID:25014641

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

2015-01-01

294

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

295

Molecular conformational analysis, vibrational spectra, NBO analysis and first hyperpolarizability of (2E)-3-(3-chlorophenyl)prop-2-enoic anhydride based on density functional theory calculations  

NASA Astrophysics Data System (ADS)

The conformational behavior and structural stability of (2E)-3-(3-chlorophenyl)prop-2-enoic anhydride were investigated by using density functional theory. The optimized molecular structure, vibrational wavenumbers, corresponding vibrational assignments of (2E)-3-(3-chlorophenyl)prop-2-enoic anhydride have been investigated experimentally and theoretically. The HOMO and LUMO analysis are used to determine the charge transfer within the molecule. The stability of the molecule arising from hyperconjugative interaction and charge delocalization has been analyzed using NBO analysis. The calculated first hyperpolarizability of the title compound is 15.8 × 10-30esu, and is 121.54 times that of the standard NLO material urea and the title compound is an attractive object for future studies of nonlinear optical properties. MEP was performed by the DFT method and the predicted infrared intensities and Raman activities have also been reported.

Mary, Y. Sheena; Raju, K.; Panicker, C. Yohannan; Al-Saadi, Abdulaziz A.; Thiemann, Thies

2014-10-01

296

Matrix isolation FT-IR, FT-Raman spectroscopy, conformational ab initio calculations, and vibrational frequencies of meso and racemic-2,4-pentanediol  

NASA Astrophysics Data System (ADS)

The infrared spectra of meso-2,4-pentanediol and racemic-2,4-pentanediol were measured in an argon matrix at 20 K. The Raman spectra of the pure liquids (meso and racemic) were measured at room temperature. The spectra were obtained using a Fourier transform spectrophotometer and a cryostat for the low temperature matrix. The meso and racemic forms of the diol were separated by means of a spinning band distillation column. The energies of nine possible conformers of the meso form and nine conformers of the racemic form were calculated. Extensive ab initio calculations using B3LYP, MP2 and HF methods with several basis sets consistently gave the lowest energy for the TT conformer of the meso form and the G-T (= TG-) conformer of the racemic form. Ab initio calculations at the B3LYP/6-31G** level were performed for the lowest energy conformer of meso and racemic pentanediol to obtain the equilibrium geometry, vibrational frequencies, and infrared and Raman intensities. Calculated and experimental frequencies were compared to make vibrational assignments.

Manzanares, Carlos E.; Reynolds, Dovie; Lewis, Ernest K.; Moehnke, Craig J.; Mina-Camilde, Nairmen; Salazar, Mary C.; Hernandez, Antonio J.

2004-02-01

297

Calculation of rotation-vibration energy levels of the water molecule with near-experimental accuracy based on an ab initio potential energy surface.  

PubMed

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. PMID:23517285

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

2013-10-01

298

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

299

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

300

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

301

Theoretical and experimental study of vibrational spectra of two polymorphic 4-hydroxy-1-methylpiperidine betaine hydrochlorides  

NASA Astrophysics Data System (ADS)

The molecular geometries, harmonic frequencies and intensities of the vibrational bands of ? and ? polymorphs of 4-hydroxy-1-methylpiperidine betaine hydrochloride (?-HO-MPBH·Cl, ?-HO-MPBH·Cl) and their deuterated derivatives have been calculated with the B3LYP/6-31G(d,p) level of theory. The calculated frequencies are compared with the solid FTIR and Raman spectra. Unequivocal assignments of the experimental infrared bands are performed on the basis of the potential energy distribution (PED).

Szafran, M.; Koput, J.; Dega-Szafran, Z.

2008-09-01

302

Theoretical and experimental study of vibrational spectra of two polymorphic 4-hydroxy-1-methylpiperidine betaine hydrochlorides  

Microsoft Academic Search

The molecular geometries, harmonic frequencies and intensities of the vibrational bands of ? and ? polymorphs of 4-hydroxy-1-methylpiperidine betaine hydrochloride (?-HO-MPBH·Cl, ?-HO-MPBH·Cl) and their deuterated derivatives have been calculated with the B3LYP\\/6-31G(d,p) level of theory. The calculated frequencies are compared with the solid FTIR and Raman spectra. Unequivocal assignments of the experimental infrared bands are performed on the basis of

M. Szafran; J. Koput; Z. Dega-Szafran

2008-01-01

303

A DFT study of the geometries and vibrational spectra of indene and some of its heterocyclic analogues, benzofuran, benzoxazole, bensothiophene, benzothiazole, indole and indazole  

NASA Astrophysics Data System (ADS)

Ab-initio optimized geometries and harmonic force fields were calculated for indene, 1; benzofuran, 2; benzoxazole, 3; benzothiophene, 4; benzothiazole, 5; indole, 6; and indazole, 7, at the HF and B3LYP levels of theory using the 6-31G** basis set. A planar Cs symmetry was assumed in all calculations. The force fields of 1- 6 were scaled with respect to the experimental frequencies available in literature. The calculated frequencies confirmed the experimental assignment of these molecules, 1- 6. The calculated scale factors were used to calculate vibrational frequencies of 7 and showed possible misassignments in the experimental vibrational frequencies of 7.

El-Azhary, A. A.

1999-10-01

304

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

305

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

306

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

307

Analysis on Non-Resonance Standing Waves and Vibration Tracks of Strings  

ERIC Educational Resources Information Center

This paper presents an experimental technique to observe the vibration tracks of string standing waves. From the vibration tracks, we can analyse the vibration directions of harmonic waves. For the harmonic wave vibrations of strings, when the driving frequency f[subscript s] = Nf[subscript n] (N = 1, 2, 3, 4,...), both resonance and non-resonance…

Fang, Tian-Shen

2007-01-01

308

Enhanced servovalve technology for seismic vibrators  

Microsoft Academic Search

The Pelton DR[trademark] Servovalve Enhancement causes the natural output of a vibrator to resemble the desired output more closely. This simplifies the control problem and reduces harmonic distortion. The traditional type of servovalve used on seismic vibrators is a flow-control servovalve. Flow is proportional to a vibrator's baseplate velocity, with respect to its reaction mass. The new servovalve control parameter

DENNIS K. REUST

1993-01-01

309

Simulation of Payload Vibration Protection by Shape Memory Alloy Parts  

NASA Astrophysics Data System (ADS)

A system of vibroisolation under consideration consists of a payload connected to a vibrating housing by plane shape memory alloy (SMA) slotted elements. The calculation of the mechanical behavior of the SMA is based on a microstructural theory. Simulations of harmonic and of impact excitations are carried out. The results have shown that protective properties of this system depend on the SMA state. The maximum reduction of the acceleration amplitude for harmonic excitation is reached when the SMA is in the martensitic (pseudo-plastic) state or in the two-phase state. A variation of temperature allows changing the resonance frequency and thus escaping from the resonance and controlling a mode of vibration.

Volkov, Aleksandr E.; Evard, Margarita E.; Red'kina, Kristina V.; Vikulenkov, Andrey V.; Makarov, Vyacheslav P.; Moisheev, Aleksandr A.; Markachev, Nikolay A.; Uspenskiy, Evgeniy S.

2014-07-01

310

Femtosecond nonlinear spectroscopy at surfaces: Second-harmonic probing of hole burning at the Si(111)7x7 surface and fourier-transform sum-frequency vibrational spectroscopy  

SciTech Connect

The high temporal resolution and broad bandwidth of a femtosecond laser system are exploited in a pair of nonlinear optical studies of surfaces. The dephasing dynamics of resonances associated with the adatom dangling bonds of the Si(111)7 x 7 surface are explored by transient second-harmonic hole burning, a process that can be described as a fourth-order nonlinear optical process. Spectral holes produced by a 100 fs pump pulse at about 800 nm are probed by the second harmonic signal of a 100 fs pulse tunable around 800 nm. The measured spectral holes yield homogeneous dephasing times of a few tens of femtoseconds. Fits with a Lorentzian spectral hole centered at zero probe detuning show a linear dependence of the hole width on pump fluence, which suggests that charge carrier-carrier scattering dominates the dephasing dynamics at the measured excitation densities. Extrapolation of the deduced homogeneous dephasing times to zero excitation density yields an intrinsic dephasing time of {approx} 70 fs. The presence of a secondary spectral hole indicates that scattering of the surface electrons with surface optical phonons at 570 cm{sup -1} occurs within the first 200 fs after excitation. The broad bandwidth of femtosecond IR pulses is used to perform IR-visible sum frequency vibrational spectroscopy. By implementing a Fourier-transform technique, we demonstrate the ability to obtain sub-laser-bandwidth spectral resolution. FT-SFG yields a greater signal when implemented with a stretched visible pulse than with a femtosecond visible pulse. However, when compared with multichannel spectroscopy using a femtosecond IR pulse but a narrowband visible pulse, Fourier-transform SFG is found to have an inferior signal-to-noise ratio. A mathematical analysis of the signal-to-noise ratio illustrates the constraints on the Fourier-transform approach.

McGuire, John Andrew

2004-11-24

311

Calculator.  

ERIC Educational Resources Information Center

Five activities are presented in this student workbook on using the electronic calculator. Following the directions for using the machine, problems are given on multiplying and dividing, finding percentages, calculating the area of assorted polygons, changing fractions to decimals, and finding squares and square roots. (JH)

Parma City School District, OH.

312

Ab Initio Calculation of the Photoelectron Spectra of the Hydroxycarbene Diradicals Lucas Koziol,  

E-print Network

in the double harmonic parallel-mode (i.e, neglecting Duschinsky rotation) approximation. Calculating to the vibrational configuration interaction spectrum; this is due to the effects of Duschinsky rotations by mass spectroscopy in the dissociative photoionization of methanol. Near the dissocia- tion threshold

Krylov, Anna I.

313

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

314

Near Spectroscopically Accurate Ab Initio Potential Energy Surface for NH4(+) and Variational Calculations of Low-Lying Vibrational Levels.  

PubMed

A nine-dimensional potential energy surface (PES) for the ammonium cation has been constructed by fitting ?30?000 AE-CCSD(T)-F12a/cc-pCVTZ-F12 points up to 32?262 cm(-1) (4.0 eV) from the minimum. The fitting using the permutation invariant polynomial-neural network method has high fidelity, with a root-mean-square error of merely 2.34 cm(-1). The low-lying vibrational energy levels of NH4(+) have been determined quantum mechanically using both Jacobi and normal coordinates, and the fundamental frequencies are in excellent agreement with available experimental data. PMID:25781209

Han, Huixian; Song, Hongwei; Li, Jun; Guo, Hua

2015-04-01

315

Comparison of Independently Calculated Ab-Initio Normal-Mode Displacements for the Three C-H Stretching Vibrations of Methanol Along the Internal Rotation Path  

NASA Astrophysics Data System (ADS)

Graphical displays of C-H stretching normal-mode coefficients from recent quantum chemical projected-frequency calculations are compared with analogous displays constructed after reexamination of results from more extensive higher-level calculations described earlier in the literature. Such comparisons confirm the facts that: (i) no geometrical phase is accumulated in these coefficients when the methyl top undergoes one complete internal-rotation revolution with respect to the frame, and (ii) some of the coefficients, when plotted against the internal rotation angle, exhibit near-cusp-like behavior at one or two angles. The connection between these graphical displays and the magnitude of "Jahn-Teller-like" and "Renner-Teller-like" torsion-vibration interaction terms in a previously reported model Hamiltonian, as well as the connection between the lack of geometric-phase accumulation in these graphs and the number of conical intersections enclosed by one full internal-rotation motion, will also be briefly discussed.

Xu, Li-Hong; Lees, Ronald; Hougen, Jon T.; Bowman, Joel; Huang, Xinchuan; Carter, Stuart

2014-06-01

316

Comparison of independently calculated ab initio normal-mode displacements for the three C-H stretching vibrations of methanol along the internal rotation path  

NASA Astrophysics Data System (ADS)

Graphical displays of normal-mode coefficients from recent quantum chemical projected-frequency calculations are compared with analogous displays constructed after reexamination of results from more extensive higher-level calculations described earlier in the literature. Such comparisons confirm the facts that: (i) no geometrical phase is accumulated in these coefficients when the methyl top undergoes one complete internal-rotation revolution with respect to the frame, and (ii) some of the coefficients, when plotted against the internal rotation angle, exhibit near-cusp-like behavior at one or two angles. The connection between these graphical displays and the magnitude of “Jahn-Teller-like” and “Renner-Teller-like” torsion-vibration interaction terms in a previously reported model Hamiltonian, as well as the connection between the lack of geometric-phase accumulation in these graphs and the number of conical intersections enclosed by one full internal-rotation motion, are briefly discussed.

Xu, Li-Hong; Lees, R. M.; Hougen, Jon T.; Bowman, Joel M.; Huang, Xinchuan; Carter, Stuart

2014-05-01

317

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

318

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

319

Intramolecular Vibrational-Energy Redistribution in Fluoroform  

NASA Astrophysics Data System (ADS)

In this study, theoretical vibrational spectra and molecular dynamics of fluoroform, developed from first principles, are presented. Particular attention is given to intramolecular vibrational-energy redistribution (IVR) present in the CH overtones which exhibit multiple time scales and thus multiple mechanisms in the IVR dynamics. A 9-dimensional ab initio potential energy surface is developed to adequately account for the vibrational couplings of all modes. Furthermore, all-mode vibrational state calculations, of large primitive space dimension, are performed using a recently developed wave operator sorting algorithm (WOSA) in tandem with the recursive residue generation method (RRGM). All fundamentals, first overtones, and bimodal combination states with up to 3 quanta are presented. Also, the A_1 and E-symmetry CH polyads are characterized through the second overtone. Equilibrium geometry, rotational constants, and vibrational properties agree quantitatively with experiment in most cases. The error is systematic in origin and largely due to the error in the ab initio harmonic frequencies. New vibrational constants and resonance interactions are reported for the background modes. In contrast to the prominent CH stretch -bend Fermi resonance structure, responsible for ultrafast (t < 50 fs) energy transfer, the CH polyads also exhibit vibrational fine-structure of order 1 to 10 cm^{-1} due to background -mode coupling. This secondary coupling results in IVR on the picosecond time scale. Modifications to the WOSA are presented, based on systematic analysis of its convergence properties for the CH fundamental and first overtone, and filtered-Lanczos eigenstate analysis is performed on these states. Finally, the IVR dynamics of the CH overtones, through upsilon_{s}=4, is assessed by explicit propagation of initial zero-order overtone states. Preliminary findings are discussed.

Maynard, Andrew Thomas

320

Harmonic engine  

Microsoft Academic Search

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

Charles L

2009-01-01

321

High-precision nonadiabatic calculations of dynamic polarizabilities and hyperpolarizabilities for low-lying vibrational-rotational states of hydrogen molecular ions  

NASA Astrophysics Data System (ADS)

The static and dynamic electric multipolar polarizabilities and second hyperpolarizabilities of the H2+,D2+, and HD+ molecular ions in the ground and first excited states are calculated nonrelativistically using explicitly correlated Hylleraas basis sets. The calculations are fully nonadiabatic; the Born-Oppenheimer approximation is not used. Comparisons are made with published theoretical and experimental results, where available. In our approach, no derivatives of energy functions nor derivatives of response functions are needed. In particular, we make contact with earlier calculations in the Born-Oppenheimer calculation where polarizabilities were decomposed into electronic, vibrational, and rotational contributions and where hyperpolarizabilities were determined from derivatives of energy functions. We find that the static hyperpolarizability for the ground state of HD+ is seven orders of magnitude larger than the corresponding dipole polarizability. For the dipole polarizability of HD+ in the first excited state the high precision of the present method facilitates treatment of a near cancellation between two terms. For applications to laser spectroscopy of trapped ions we find tune-out and magic wavelengths for the HD+ ion in a laser field. In addition, we also calculate the first few leading terms for long-range interactions of a hydrogen molecular ion and a ground state H, He, or Li atom.

Tang, Li-Yan; Yan, Zong-Chao; Shi, Ting-Yun; Babb, James F.

2014-07-01

322

Determination of the absolute configurations of natural products via density functional theory calculations of vibrational circular dichroism, electronic circular dichroism, and optical rotation: The iso-schizozygane alkaloids isoschizogaline and isoschizogamine  

Microsoft Academic Search

The development of density functional theory (DFT) methods for the calculation of vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and transparent spectral region optical rotation (OR) has revolutionized the determination of the absolute configurations (ACs) of chiral molecules using these chi- roptical properties. We report the concerted application of DFT calculations of VCD, ECD, and OR to the determination

Philip J. Stephens; Jian-Jung Pan; Frank J. Devlin; MARIE URBANOVA ´; EJ JULINEK; JOSEF HAJIC

2008-01-01

323

Deducing the molecular properties of zwitterionic, protonated, deprotonated, and double-deprotonated forms of L-cysteine from vibrational spectroscopy (IR, Raman, VCD) and quantum chemical calculations.  

PubMed

The behavior of L-cysteine (C3H7NO2S, (2R)-2-amino-3-sulfanylpropanoic acid) in water at different pH values was analyzed both experimentally and theoretically. The behavior was studied at pH values of 5.21 (at this pH, L-cysteine is a zwitterionic species), 1.00 (protonated species), 8.84 (monodeprotonated species), and 13.00 (dideprotonated species). We carried out a vibrational study using nonchiroptical (IR-Raman) and chiroptical (VCD) techniques complemented by quantum chemical calculations. We adopted a dual strategy, as follows. (i) The hybrid density functionals B3LYP and M062X and the ab initio MP2 method were employed, with the same 6-311++G (d,p) basis set, in order to characterize the relative energies and structures of an extensive set of conformers of L-cysteine. The presence of water was included by utilizing the IEF-PCM implicit solvation model. (ii) The vibrational analysis was made using a chirality-sensitive using a chirality-sensitive technique (VCD) and chirality-insensitive techniques (IR, including MIR and FIR, and Raman), especially in aqueous solution. The results obtained theoretically and experimentally were compared in order to deduce the most stable structures at each pH. Moreover, for the first time, the monodeprotonated anion of L-cysteine was detected in aqueous solution by means of IR, Raman and vibrational circular dichroism (VCD). Finally, analysis of the low-frequency region using the IR and Raman techniques was shown to be a very important way to understanding the conformational preference of the zwitterionic species. PMID:24916344

Quesada-Moreno, María Mar; Avilés-Moreno, Juan Ramón; Márquez-García, A A; López-González, Juan Jesús

2014-06-01

324

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...

325

Discriminating harmonicity  

NASA Astrophysics Data System (ADS)

Simultaneous tones that are harmonically related tend to be grouped perceptually to form a unitary auditory image. A partial that is mistuned stands out from the other tones, and harmonic complexes with different fundamental frequencies can readily be perceived as separate auditory objects. These phenomena are evidence for the strong role of harmonicity in perceptual grouping and segregation of sounds. This study measured the discriminability of harmonicity directly. In a two interval, two alternative forced-choice (2I2AFC) paradigm, the listener chose which of two sounds, signal or foil, was composed of tones that more closely matched an exact harmonic relationship. In one experiment, the signal was varied from perfectly harmonic to highly inharmonic by adding frequency perturbation to each component. The foil always had 100% perturbation. Group mean performance decreased from greater than 90% correct for 0% signal perturbation to near chance for 80% signal perturbation. In the second experiment, adding a masker presented simultaneously with the signals and foils disrupted harmonicity. Both monaural and dichotic conditions were tested. Signal level was varied relative to masker level to obtain psychometric functions from which slopes and midpoints were estimated. Dichotic presentation of these audible stimuli improved performance by 3-10 dB, due primarily to a release from ``informational masking'' by the perceptual segregation of the signal from the masker.

Kidd, Gerald; Mason, Christine R.; Brughera, Andrew; Chiu, Chung-Yiu Peter

2003-08-01

326

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

327

Ab initio molecular dynamics with noisy forces: validating the quantum Monte Carlo approach with benchmark calculations of molecular vibrational properties.  

PubMed

We present a systematic study of a recently developed ab initio simulation scheme based on molecular dynamics and quantum Monte Carlo. In this approach, a damped Langevin molecular dynamics is employed by using a statistical evaluation of the forces acting on each atom by means of quantum Monte Carlo. This allows the use of an highly correlated wave function parametrized by several variational parameters and describing quite accurately the Born-Oppenheimer energy surface, as long as these parameters are determined at the minimum energy condition. However, in a statistical method both the minimization method and the evaluation of the atomic forces are affected by the statistical noise. In this work, we study systematically the accuracy and reliability of this scheme by targeting the vibrational frequencies of simple molecules such as the water monomer, hydrogen sulfide, sulfur dioxide, ammonia, and phosphine. We show that all sources of systematic errors can be controlled and reliable frequencies can be obtained with a reasonable computational effort. This work provides convincing evidence that this molecular dynamics scheme can be safely applied also to realistic systems containing several atoms. PMID:25416879

Luo, Ye; Zen, Andrea; Sorella, Sandro

2014-11-21

328

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

329

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.  

PubMed

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. PMID:24992920

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

2014-12-10

330

Calculation of the vibrational excited states of malonaldehyde and their tunneling splittings with the multi-configuration time-dependent Hartree method  

NASA Astrophysics Data System (ADS)

We report energies and tunneling splittings of vibrational excited states of malonaldehyde which have been obtained using full dimensional quantum mechanical calculations. To this end we employed the multi configuration time-dependent Hartree method. The results have been obtained using a recently published potential energy surface [Y. Wang, B. J. Braams, J. M. Bowman, S. Carter, and D. P. Tew, J. Chem. Phys. 128, 224314 (2008)] which has been brought into a suitable form by a modified version of the n-mode representation which was used with two different arrangements of coordinates. The relevant terms of the expansion have been identified with a Metropolis algorithm and a diffusion Monte-Carlo technique, respectively.

Schröder, Markus; Meyer, Hans-Dieter

2014-07-01

331

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

332

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

333

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

PubMed

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 O-H···O and intramolecular C-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. PMID:23466319

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

2013-05-01

334

Towards black-box calculations of tunneling splittings obtained from vibrational structure methods based on normal coordinates.  

PubMed

Multidimensional potential energy surfaces obtained from explicitly correlated coupled-cluster calculations and further corrections for high-order correlation contributions, scalar relativistic effects and core-correlation energy contributions were generated in a fully automated fashion for the double-minimum benchmark systems OH3(+) and NH3. The black-box generation of the potentials is based on normal coordinates, which were used in the underlying multimode expansions of the potentials and the ?-tensor within the Watson operator. Normal coordinates are not the optimal choice for describing double-minimum potentials and the question remains if they can be used for accurate calculations at all. However, their unique definition is an appealing feature, which removes remaining errors in truncated potential expansions arising from different choices of curvilinear coordinate systems. Fully automated calculations are presented, which demonstrate, that the proposed scheme allows for the determination of energy levels and tunneling splittings as a routine application. PMID:23548204

Neff, Michael; Rauhut, Guntram

2014-02-01

335

Raman spectrum, quantum mechanical calculations and vibrational assignments of (95% alpha-TeO2/5% Sm2O3) glass.  

PubMed

Chozen system of tellurite glasses doped with rare earth oxides (95% alpha-TeO(2)+5% Sm2O3) was prepared by melt quenching. Consequently, the Raman spectrum (150-1250 cm(-1)) of the modified tellurite have been recorded. As a continuation to our normal coordinate analysis, force constants and quantum mechanical (QM) calculations for tbp TeO4(4-) (triagonal bipyramid, C(2v)) and TeO(3+1); Te2O7(6-) (bridged tetrahedral), we have carried out ab initio frequency calculations for tpy TeO3(2-) (triagonal pyramidal, C(3v) and C(s)) and tp TeO3(2-) (triagonal planar, D(3h)) ions. The quantum mechanical calculations at the levels of RHF, B3LYP and MP2 allow confident vibrational assignments and structural identification in the binary oxide glass (95% alpha-TeO2 +5% Sm2O3). The dominant three-dimensional network structures in the modified glass are triagonal pyramidal TeO3 with minor features of short range distorted tbp TeO4 and bridged tetrahedral unit of TeO(3+1), leading to a structure of infinite chain. Therefore, alpha-TeO2/Sm2O3 (95/5%) glass experience structural changes from TeO4 (tbp); Te2O7 (TeO(3+1))-->TeO3 (tpy). PMID:16982208

Shaltout, I; Mohamed, Tarek A

2007-06-01

336

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

337

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

NASA Astrophysics Data System (ADS)

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 13C NMR and 1H 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.

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

2015-03-01

338

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

339

Efficient configuration selection scheme for vibrational second-order perturbation theory  

NASA Astrophysics Data System (ADS)

A fast algorithm of vibrational second-order Møller-Plesset perturbation theory is proposed, enabling a substantial reduction in the number of vibrational self-consistent-field (VSCF) configurations that need to be summed in the calculations. Important configurations are identified a priori by assuming that a reference VSCF wave function is approximated well by harmonic oscillator wave functions and that fifth- and higher-order anharmonicities are negligible. The proposed scheme has reduced the number of VSCF configurations by more than 100 times for formaldehyde, ethylene, and furazan with an error in computed frequencies being not more than a few cm-1.

Yagi, Kiyoshi; Hirata, So; Hirao, Kimihiko

2007-07-01

340

Efficient configuration selection scheme for vibrational second-order perturbation theory.  

PubMed

A fast algorithm of vibrational second-order Moller-Plesset perturbation theory is proposed, enabling a substantial reduction in the number of vibrational self-consistent-field (VSCF) configurations that need to be summed in the calculations. Important configurations are identified a priori by assuming that a reference VSCF wave function is approximated well by harmonic oscillator wave functions and that fifth- and higher-order anharmonicities are negligible. The proposed scheme has reduced the number of VSCF configurations by more than 100 times for formaldehyde, ethylene, and furazan with an error in computed frequencies being not more than a few cm(-1). PMID:17655435

Yagi, Kiyoshi; Hirata, So; Hirao, Kimihiko

2007-07-21

341

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

342

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

343

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

344

Calculation of Anharmonicities in Overtone Modes and Small-Cluster Shifts of Spherical-Top Molecules  

NASA Astrophysics Data System (ADS)

Harmonic and anharmonic vibrational self-consistent field (VSCF) calculations were employed to investigate the fundamental and overtone modes of SF6 molecules. Determination of the Potential Energy Surface (PES) on a multidimensional grid of more than 65000 nodes was performed, and a system of 1D coupled-equations was solved. Corrections to the harmonic approximation for the frequencies of the fundamental modes and their overtones were obtained. Ab-initio calculations to the interaction potential between two molecules as a function of their position and orientation, and the corresponding energies for dimer formation, have been computed. Finally, the effect of dimerization on the molecular frequencies is investigated.

Fuhr, Javier D.; Fiol, Juan; Cortizo, Eduardo; Fainstein, Pablo D.; Fregenal, Daniel E.; Guozden, Tomás; Kaúl, Enrique; Knoblauch, Pablo; Lamagna, Alberto; Maceira, Pablo; Rozas, Guillermo; Zarco, Martín

2014-06-01

345

Application of vibrational spectroscopy supported by theoretical calculations in identification of amorphous and crystalline forms of cefuroxime axetil.  

PubMed

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

Talaczy?ska, Alicja; Lewandowska, Kornelia; Jeli?ska, Anna; Garbacki, Piotr; Podborska, Agnieszka; Zalewski, Przemys?aw; Oszczapowicz, Irena; Sikora, Adam; Kozak, Maciej; Cielecka-Piontek, Judyta

2015-01-01

346

Melting of ?-Al2O3 and vitrification of the undercooled alumina liquid: ab initio vibrational calculations and their thermodynamic implications.  

PubMed

We present the results of a computational investigation of the structure-energy and vibrational properties of alumina under various aggregation states (crystalline, glassy, and liquid) with ab initio procedures. IV-fold, V-fold, and VI-fold oxygen-coordinated aluminum monomeric forms in a dielectric continuum with dielectric constant ? = 4.575 were investigated through DFT/B3LYP gas-phase calculations coupled with a Polarized Continuum Model approach and those of the periodical structure D(6)(3d) (R-3c) which leads to the ?-Al(2)O(3) polymorph of alumina, when subjected to symmetry operations, were investigated with the same functional within the LCAO approximation and in the framework of Bloch's theorem. Based on the computed energies and vibrational features, an aggregate of the D(6)(3d) positively charged cluster [Al(12)O(11)](14+) contoured by [AlO(4)](5-) units in an approximate 1:3 proportion to achieve neutrality satisfactorily reproduce the heat capacity of the liquid within experimental uncertainty. The glass is seen as a wrong accretionary form induced by fast cooling rates and subjected to steric forces that locally modify the coordination state of the central atom. Cessation of rotational and translational movements, only partly counterbalanced by acoustic sine-wave-dispersed and excess phonons, gives rise to the huge heat-capacity gap observed at the glass transition (~5.3R). When cooling rates are sufficiently slow, the accretion around the D(6)(3d) seeds follows the structural constraints and the heat capacity of ?-alumina is almost perfectly reproduced by the 27 Einstein oscillators coupled with the 3 acoustic terms and the anharmonic corrections. PMID:23425479

Belmonte, D; Ottonello, G; Vetuschi Zuccolini, M

2013-02-14

347

Melting of ?-Al2O3 and vitrification of the undercooled alumina liquid: Ab initio vibrational calculations and their thermodynamic implications  

NASA Astrophysics Data System (ADS)

We present the results of a computational investigation of the structure-energy and vibrational properties of alumina under various aggregation states (crystalline, glassy, and liquid) with ab initio procedures. IV-fold, V-fold, and VI-fold oxygen-coordinated aluminum monomeric forms in a dielectric continuum with dielectric constant ? = 4.575 were investigated through DFT/B3LYP gas-phase calculations coupled with a Polarized Continuum Model approach and those of the periodical structure D63d (R-3c) which leads to the ?-Al2O3 polymorph of alumina, when subjected to symmetry operations, were investigated with the same functional within the LCAO approximation and in the framework of Bloch's theorem. Based on the computed energies and vibrational features, an aggregate of the D63d positively charged cluster [Al12O11]14+ contoured by [AlO4]5- units in an approximate 1:3 proportion to achieve neutrality satisfactorily reproduce the heat capacity of the liquid within experimental uncertainty. The glass is seen as a wrong accretionary form induced by fast cooling rates and subjected to steric forces that locally modify the coordination state of the central atom. Cessation of rotational and translational movements, only partly counterbalanced by acoustic sine-wave-dispersed and excess phonons, gives rise to the huge heat-capacity gap observed at the glass transition (˜5.3R). When cooling rates are sufficiently slow, the accretion around the D63d seeds follows the structural constraints and the heat capacity of ?-alumina is almost perfectly reproduced by the 27 Einstein oscillators coupled with the 3 acoustic terms and the anharmonic corrections.

Belmonte, D.; Ottonello, G.; Zuccolini, M. Vetuschi

2013-02-01

348

Conformational stability, vibrational assignments, and normal coordinate analysis from FT-IR spectra of xenon solutions and ab initio calculations of epichlorohydrin  

NASA Astrophysics Data System (ADS)

Infrared spectra (3500-400 cm -1) of epichlorohydrin (chloromethyloxirane), c-OC 2H 3C(Cl)H 2, dissolved in liquid xenon have been recorded at several temperatures from -40 to -105°C. Additionally, the Raman spectrum of the liquid has been obtained from 23 to -39°C. These spectra are consistent with three stable conformers existing in both phases at ambient temperature. The data have been interpreted on the basis that the gauche-2 conformer is the most stable form and the gauche-1 rotamer (most polar) is the second most stable form in the xenon solution whereas the gauche-1 conformer is the most stable form and the cis conformer is the second most stable form in the liquid. Utilizing well separated triplets of three fundamentals due to all three conformers, the enthalpy differences have been determined to be 51 ± 14 cm -1 (146 ± 40 cal mol -1) (gauche-2 to gauche-1) and 213 ± 97 cm -1 (609 ± 277 cal mol -1) (gauche-2 to cis) in the xenon solution and 383 ± 28 cm -1 (gauche-1 to gauche-2) and 358 ± 12 cm -1 (gauche-1 to cis) in the liquid. The structural parameters, dipole moments, conformational stability, and vibrational frequencies have been determined by ab initio calculations with two basis sets up to MP2/6-31G?. Vibrational assignments for the 24 normal modes for both the gauche-2 and gauche-1 conformers are proposed with several of the fundamentals assigned for the cis conformer. In addition, some of the fundamental frequencies for motions of the 37Cl isotope have been observed at 2-3 cm -1 lower frequency than the corresponding modes of the 35Cl isotope.

Lee, Min Joo; Hur, Seung Won; Durig, James R.

1998-03-01

349

Structural and vibrational investigation on species derived from the cyclamic acid in aqueous solution by using HATR and Raman spectroscopies and SCRF calculations  

NASA Astrophysics Data System (ADS)

In this study, aqueous solutions at different molar concentrations of sodium cyclamate in water were completely characterized by HATR (Horizontal Attenuated Total Reflectance) and Raman spectroscopies. The theoretical structures of cyclamate ion, the zwitterionic and neutral forms of the cyclamic acid and its dimer were optimized in gas and aqueous solution phases by using the hybrid B3LYP/6-31G* method. The solvent effects for the four species in aqueous solutions were simulated by using self-consistent reaction field (SCRF) calculations employing the integral equation formalism variant (IEFPCM) model. The complete assignments of the vibrational spectra of all the forms of cyclamic acid were performed taking into account the factor group analysis with the Scaled Quantum Mechanics Force Field (SQMFF) methodology. The existence of the zwitterionic and neutral forms of the cyclamic acid and its dimer in a solution of cyclamate in water is evidenced by characteristic bands in the HATR and Raman spectra. The dimerization of cyclamate in aqueous solution was previously reported by conductimetric method. The natural population analysis (NPA) and Merz-Kollman (MK) charges, molecular electrostatic potential (MEP), natural bond orbital (NBO) and atoms in molecules (AIM) calculations predict for all the species the principal donor and acceptor sites for the H bonds formation in aqueous solution. The SQM force fields for the cyclamate ion, the zwitterionic and neutral species of the cyclamic acid were obtained and their corresponding force constants in both phases were reported. Additionally, the solvation energies for those species were reported.

Brizuela, Alicia B.; Raschi, Ana B.; Castillo, María V.; Davies, Lilian; Romano, Elida; Brandán, Silvia A.

2014-09-01

350

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

351

A First Principles Density-Functional Calculation of the Electronic and Vibrational Structure of the Key Melanin Monomers  

E-print Network

We report first principles density functional calculations for hydroquinone (HQ), indolequinone (IQ) and semiquinone (SQ). These molecules are believed to be the basic building blocks of the eumelanins, a class of bio-macromolecules with important biological functions (including photoprotection) and with potential for certain bioengineering applications. We have used the DeltaSCF (difference of self consistent fields) method to study the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), Delta_HL. We show that Delta_HL is similar in IQ and SQ but approximately twice as large in HQ. This may have important implications for our understanding of the observed broad band optical absorption of the eumelanins. The possibility of using this difference in Delta_HL to molecularly engineer the electronic properties of eumelanins is discussed. We calculate the infrared and Raman spectra of the three redox forms from first principles. Each of the molecules have significantly different infrared and Raman signatures, and so these spectra could be used in situ to non-destructively identify the monomeric content of macromolecules. It is hoped that this may be a helpful analytical tool in determining the structure of eumelanin macromolecules and hence in helping to determine the structure-property-function relationships that control the behaviour of the eumelanins.

B. J. Powell; T. Baruah; N. Bernstein; K. Brake; Ross H. McKenzie; P. Meredith; M. R. Pederson

2004-01-23

352

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

353

Towards an understanding of the vibrational spectrum of the neutral Au7 cluster.  

PubMed

We present a detailed theoretical study of the vibrational spectrum of the neutral Au(7) cluster, aimed at understanding its reported experimental spectrum [P. Gruene et al., Science, 2008, 321, 674]. We study the effect of vibrational anharmonicity, polymorphism, noble gas embedding, and the use of various electronic-structure methods. We use a vibrational configuration-interaction approach (VCI) with a vibrational self-consistent field (VSCF) basis, in order to study the effect of vibrational anharmonicity for the density functional theory (DFT) global minimum energy structure. Our implementation of the VSCF/VCI method is based on the direct calculation of the potential energy surface (PES) using pseudo potential plane-wave DFT. An efficient reduction of the number of mode-mode couplings between vibrational modes (fast-VSCF/VCI) is used to speed up calculations. We show that the rather small anharmonicity does not account for the difference between harmonic and experimental frequencies and consequently for the large global scaling factor, reported by the authors of the experiment. Instead, the use of different electronic structure methods allows for a significant reduction of the scaling factor. We also show that krypton embedding does not significantly change the vibrational frequencies of the Au(7) cluster. PMID:23258549

Mancera, Luis A; Benoit, David M

2013-02-14

354

Experimental and ab Initio Equilibrium Structure and Harmonic Force Field of 1,2,5-Oxadiazole  

Microsoft Academic Search

The equilibrium structure of 1,2,5-oxadiazole has been calculated ab initio at the CCSD(T) level using a polarized valence quadruple ? basis set. The harmonic force field has also been calculated at the MP2\\/cc-pVTZ, B3LYP\\/6-311++G(3df, 2pd), and B3LYP\\/cc-pVQZ levels. These force fields have been subsequently scaled and further refined by fitting them to the experimental values of the vibrational fundamentals of

J. Vázquez; J. Demaison; J. J. López-González; James E Boggs; H. D Rudolph

2001-01-01

355

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

356

Harmonic generation at high intensities  

SciTech Connect

Atomic electrons subject to intense laser fields can absorb many photons, leading either to multiphoton ionization or the emission of a single, energetic photon which can be a high multiple of the laser frequency. The latter process, high-order harmonic generation, has been observed experimentally using a range of laser wavelengths and intensities over the past several years. Harmonic generation spectra have a generic form: a steep decline for the low order harmonics, followed by a plateau extending to high harmonic order, and finally an abrupt cutoff beyond which no harmonics are discernible. During the plateau the harmonic production is a very weak function of the process order. Harmonic generation is a promising source of coherent, tunable radiation in the XUV to soft X-ray range which could have a variety of scientific and possibly technological applications. Its conversion from an interesting multiphoton phenomenon to a useful laboratory radiation source requires a complete understanding of both its microscopic and macroscopic aspects. We present some recent results on the response of single atoms at intensities relevant to the short pulse experiments. The calculations employ time-dependent methods, which we briefly review in the next section. Following that we discuss the behavior of the harmonics as a function of laser intensity. Two features are notable: the slow scaling of the harmonic intensities with laser intensity, and the rapid variation in the phase of the individual harmonics with respect to harmonic order. We then give a simple empirical formula that predicts the extent of the plateau for a given ionization potential, wavelength and intensity.

Schafer, K.J.; Krause, J.L.; Kulander, K.C.

1993-06-01

357

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

NASA Astrophysics Data System (ADS)

The vibrational absorption (IR) and vibrational circular dichroism (VCD) spectra of alanine dipeptide analog in water are directly calculated by Fourier transforming the time correlation functions of the electric and magnetic dipole moments, which are calculated using the dynamic partial charges and trajectory of the peptide generated from the quantum mechanical/molecular mechanical molecular dynamics simulations. The alanine dipeptide analog is treated at the Hartree-Fock level with 3-21G, 4-31G, 6-31G, and 6-31G? basis sets and the solvent H2O is modeled with the TIP3P water. The atomic partial charges are obtained from the Löwdin population analysis, which gives consistent IR spectral profiles irrespective of the basis sets used. The simulated VCD spectrum by a polyproline II(PII)-dominant trajectory is compatible with the previous experimental results of the polyproline peptides, where the amide I and II VCD bands are negative couplets with a weak positive peak to the high frequency region. The sampling efficiency of the PII conformer is much lower than the other ones at all basis levels used. The simulated VCD spectrum of ?-helix averaged over five trajectories has the reverse sign pattern compared to the PII spectrum and is found to be consistent with the previously observed spectral features of ?-helical polypeptides. The sign patterns of the ?-strand VCD spectrum are qualitatively similar to the experimental spectra of ?-sheet rich proteins. The VCD spectra obtained from the trajectories containing several extended conformers such as ? and PII are not clearly distinguishable from the ?-strand-dominant spectra. It is interesting that the PII and the coil VCD spectra coincide in sign pattern and relative intensity for all amide modes. This demonstrates that the negative couplet structures of the amide I and II VCD spectra do not necessarily prove the dominance of either PII or coil conformation. We anticipate that the present method can be used to directly simulate the IR and VCD spectra of structurally heterogeneous biomolecules in condensed phases.

Yang, Seongeun; Cho, Minhaeng

2009-10-01

358

The role of vibrations in thermodynamic properties of Cu-Ni alloys  

NASA Astrophysics Data System (ADS)

We report results of a systematic study for vibrational thermodynamic functions of Cu-Ni alloys, in the harmonic approximation, using interaction potentials based on the embedded atom method with improved optimization techniques. The vibrational density of states of the systems is calculated using real space Green's function method. From an investigation of local force fields we found that increasing Ni concentration in the alloy substantially stiffens the force experienced by Cu atoms compared to that of Ni atoms. Our calculations also reveal that vibrational entropy change between ordered and disordered crystals of Cu-Ni is negligible. However, the mixing entropy of the phonons and electronic states is found to be negative and favors un-mixing, and thus contributes to the miscibility gap.

Onat, Berk; Durukano?lu, Sondan

2014-11-01

359

Vibrational spectroscopy of triacetone triperoxide (TATP): anharmonic fundamentals, overtones and combination bands.  

PubMed

The vibrational spectrum of triacetone triperoxide (TATP) is studied by the correlation-corrected vibrational self-consistent field (CC-VSCF) method which incorporates anharmonic effects. Fundamental, overtone, and combination band frequencies are obtained by using a potential based on the PM3 method and yielding the same harmonic frequencies as DFT/cc-pVDZ calculations. Fundamentals and overtones are also studied with anharmonic single-mode (without coupling) DFT/cc-pVDZ calculations. Average deviations from experiment are similar for all methods: 2.1-2.5%. Groups of degenerate vibrations form regions of numerous combination bands with low intensity: the 5600-5800 cm(-1) region contains ca. 70 overtones and combinations of CH stretches. Anharmonic interactions are analyzed. PMID:18554978

Brauer, Brina; Dubnikova, Faina; Zeiri, Yehuda; Kosloff, Ronnie; Gerber, R Benny

2008-12-15

360

Vibrational spectroscopy of triacetone triperoxide (TATP): Anharmonic fundamentals, overtones and combination bands  

NASA Astrophysics Data System (ADS)

The vibrational spectrum of triacetone triperoxide (TATP) is studied by the correlation-corrected vibrational self-consistent field (CC-VSCF) method which incorporates anharmonic effects. Fundamental, overtone, and combination band frequencies are obtained by using a potential based on the PM3 method and yielding the same harmonic frequencies as DFT/cc-pVDZ calculations. Fundamentals and overtones are also studied with anharmonic single-mode (without coupling) DFT/cc-pVDZ calculations. Average deviations from experiment are similar for all methods: 2.1-2.5%. Groups of degenerate vibrations form regions of numerous combination bands with low intensity: the 5600-5800 cm -1 region contains ca. 70 overtones and combinations of CH stretches. Anharmonic interactions are analyzed.

Brauer, Brina; Dubnikova, Faina; Zeiri, Yehuda; Kosloff, Ronnie; Gerber, R. Benny

2008-12-01

361

Analysis of a high Tc superconducting levitation system with vibration isolation control  

SciTech Connect

This paper presents a method for controlling vibrations of a levitated high Tc superconducting body subjected to base disturbances. To have the control forces, an actuator consisting of a permanent magnet with an electromagnet was presented. The analytical solution for calculating levitation forces due to the permanent magnet and the control currents in the electromagnet was obtained. The levitation forces obtained coincide with the previously published results. The equation of motion of the levitated body subjected to base disturbances under the control was presented. Nonlinear vibrations of the body were first discussed; then the method of vibration isolation control using the direct disturbance cancellation combining the velocity feedback control was investigated. Numerical calculations were carried out for the levitation forces, with respect to the levitated body subjected to harmonic or pulse base excitations. It was clarified that the present method is valid for controlling nonlinear systems like the magnetic levitated superconducting body.

Nagaya, Kosuke [Gunma Univ., Kiryu, Gunma (Japan). Dept. of Mechanical Engineering] [Gunma Univ., Kiryu, Gunma (Japan). Dept. of Mechanical Engineering

1996-03-01

362

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

363

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.

364

Analysis of 3-D vibrations from time-averaged holograms.  

PubMed

In a previous paper [R. Tonin and D. A. Bies, J. Sound Vib. 52(3), 315 (1977)] the theory of time-averaged holographic interferometry was extended to include simple harmonic motion in three orthogonal directions at a single frequency. The amended characteristic function formula was used to calculate the radial and tangential components of a vibrating cylinder by first determining the radial component and from this the tangential component of vibration. In this paper the analysis of the previous paper is improved by making use of a technique originally introduced for the investigation of static deflection using time-averaged holography [S. K. Dhir and J. P. Sikora, Exp. Mech. 12(7), 323 (1972)]. The improved procedure allows simultaneous determination of all vibration amplitude components. The procedure is used for the investigation of the low order resonant vibration modes of four cylinders of various sizes and materials with shear-diaphragm end conditions with good results. The procedure is quite general in its application and not restricted to the study of cylinders. It lends itself easily to the study of coupled-mode vibration problems and in fact many complex resonance phenomena. PMID:20208598

Tonin, R; Bies, D A

1978-12-01

365

Vibration modes of giant gravitons  

Microsoft Academic Search

We examine the spectrum of small vibrations of giant gravitons when the gravitons expand in anti--de Sitter space and when they expand on the sphere. For any given angular harmonic, the modes are found to have frequencies related to the curvature length scale of the background; these frequencies are independent of radius (and hence angular momentum) of the brane itself.

Sumit R. Das; Antal Jevicki; Samir D. Mathur

2001-01-01

366

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

367

Adaptive harmonic steady state control for disturbance rejection  

Microsoft Academic Search

We develop an adaptive harmonic steady state control for disturbance rejection. HSS control extends higher harmonic control and convergent control developed for helicopter vibration reduction and rotor imbalance control. HSS control is applicable to stable systems with tonal or multi-tonal disturbances. The adaptive HSS algorithm is easy to implement and robust in the sense that no modeling information is required

J. Chandrasekar; L. Liu; D. Patt; P. P. Friedmann; D. S. Bernstein

2004-01-01

368

Molecular structure, vibrational spectroscopic, first-order hyperpolarizability and HOMO, LUMO studies of 2-aminobenzimidazole.  

PubMed

In the present work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and HOMO-LUMO analysis of 2-aminobenzimidazole (2-ABD). The FTIR (400-4000 cm(-1)) and FT-Raman spectra (50-3500 cm(-1)) of 2-ABD were recorded. The molecular geometry, harmonic vibrational wavenumbers and bonding features of 2-ABD in the ground-state have been calculated by using the density functional B3LYP method with 6-311++G(d,p) and 6-31G(d) as basis sets. The energy and oscillator strength were calculated by time-dependent density functional theory (TD-DFT) result complements with the experimental findings. The calculated HOMO and LUMO energies showed that charge transfer occurs within the molecule. Finally, the calculation results were applied to simulate infrared and Raman spectra of the title compound which showed good agreement with the observed spectra. PMID:21981941

Sudha, S; Karabacak, M; Kurt, M; Cinar, M; Sundaraganesan, N

2011-12-15

369

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

370

Vibrational wave functions and energy levels of large anharmonic clusters: A vibrational SCF study of (Ar)13  

NASA Astrophysics Data System (ADS)

The vibrational ground state and the fundamental excited states of (Ar)13 were studied by vibrational self-consistent field (VSCF) calculations. These calculations treat the interaction between different modes through a mean potential approximation, and incorporate anharmonicity in full. The good accuracy of VSCF for such systems was demonstrated by test calculations for (Ar)3 and other clusters. The study of (Ar)13 focused on the properties of the wave functions and the excitation energies, on the role of the coupling between the modes and on the deviation from the harmonic approximation. It was found that SCF excitation energies for the fundamental transitions differ from the harmonic values by about 25% for the softest modes, and by about 10% for the stiffest modes. Coupling between the modes, treated by SCF, was found to be much more important than the intrinsic anharmonicity of the individual modes. For the ground state, the harmonic wave function compares well with VSCF, but for the fundamental excited states appreciable differences were found. The results for a potential field expanded to fourth-order polynomial in the normal mode displacements are found to be valid, almost indentical with those for a more elaborate sixth-order polynomial expansion. The fundamental excitation frequencies computed using the Aziz-Slaman Ar-Ar pair potential are very similar, with some quantitative deviations, to the values obtained with a Lennard-Jones potential. The differences are larger for certain specific modes, and very small for the others. These calculations demonstrate the computational power of VSCF as a tool for quantum-mechanical calculations for large clusters, at the level of specific wave functions.

Jung, Joon O.; Gerber, R. Benny

1996-12-01

371

Twelfth International Congress on Sound and Vibration  

E-print Network

the inherent physics of underground railway vibration and to control the vibrations propagating from the tunnel FOR VIBRATIONS FROM UNDERGROUND RAILWAY TRAFFIC S. Gupta, M.F.M Hussein, R. Klein, G. Degrande, H.E.M. Hunt K Abstract Two prediction models for calculating the vibration from underground railways were devel- oped

Talbot, James P.

372

Dioxirane vibrational frequencies: an unsettling relationship between theory and experiment  

NASA Astrophysics Data System (ADS)

There appears to be a conflict between theory and experiment concerning the vibrational frequencies of dioxirane, a CH2O2 isomer. Here we employ sophisticated ab initio quantum mechanical methods with large basis sets to determine geometry, harmonic vibrational frequencies, infrared (IR) intensities and isotopic shifts of dioxirane. At the highest level of theory, the CCSD(T) approach is used together with a cc-VTZ2P+f,d basis set. Best predictions for CO asymmetric and OO stretching (or OCO deformation) harmonic frequencies are 931 (b2)cm-1 and 759 (a2)cm-1, respectively. The IR intensities of these two peaks are predicted to be 19 km mol-1 and 1 km mol-1. An examination of the experimental vibrational frequencies of substituted dioxiranes is also presented. Calculated frequencies, intensities, and isotopic shifts all imply that the two experimental IR features (with their observed intensity ratio of 2?8) assigned to CO stretching (839.0 cm-1) and OCO deformation (800.9 cm-1) frequencies by J. R. Sodeau and L. J. Whyte (1991, J. chem. Soc. Faraday Trans., 87, 3725) should be re-addressed.

Kraka, Elfi

373

Harmonic Electromagnetic Forces in Induction Motors  

Microsoft Academic Search

Recently, there has been increasing demand for quiet motors, and the same trend has been observed in the case of induction motors. In induction motors, electromagnetic noise is sometimes the predominant acoustic noise. In small motors, the major cause of vibration and noise is electromagnetic forces resulting from the combination of harmonic fluxes in the air gap. In this study,

Fuminori Ishibashi; Makoto Matsushita; Shinichi Noda

2009-01-01

374

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

375

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

376

Spectroscopic analysis and DFT calculations of a food additive Carmoisine  

NASA Astrophysics Data System (ADS)

FT-IR and Raman techniques were employed for the vibrational characterization of the food additive Carmoisine (E122). The equilibrium geometry, various bonding features, and harmonic vibrational wavenumbers have been investigated with the help of density functional theory (DFT) calculations. A good correlation was found between the computed and experimental wavenumbers. Azo stretching wavenumbers have been lowered due to conjugation and ?-electron delocalization. Predicted electronic absorption spectra from TD-DFT calculation have been analysed comparing with the UV-vis spectrum. The first hyperpolarizability of the molecule is calculated. Intramolecular charge transfer (ICT) responsible for the optical nonlinearity of the dye molecule has been discussed theoretically and experimentally. Stability of the molecule arising from hyperconjugative interactions, charge delocalization and C-H⋯O, improper, blue shifted hydrogen bonds have been analysed using natural bond orbital (NBO) analysis.

Snehalatha, M.; Ravikumar, C.; Hubert Joe, I.; Sekar, N.; Jayakumar, V. S.

2009-04-01

377

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

378

Determination of the absolute configuration of chiral molecules via density functional theory calculations of vibrational circular dichroism and optical rotation: The chiral alkane D 3 -anti-trans-anti-trans-anti-trans-perhydrotriphenylene  

Microsoft Academic Search

The Absolute configuration (AC) of the chiral alkane D3-anti-trans-anti-trans-anti-trans-perhydrotriphenylene (PHTP), 1, is determined by comparison of density functional theory (DFT) calculations of its vibrational circular dichroism (VCD)\\u000a and optical rotation (OR) to the experimental VCD and OR of (+)?1, obtained in high enantiomeric excess using chiral gas chromatography. Conformational analysis of 1 demonstrates that the all-chair (CCCC) conformation is the

P. J. Stephens; F. J. Devlin; S. Schürch; J. Hulliger

2008-01-01

379

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

380

Vibrational optical activity in deuteriated phenylethanes  

SciTech Connect

Infrared, Raman, and vibrational circular dichroism (VCD) spectra have been recorded in the region 3100-2000 cm/sup -1/ for (S)-(+)-1-phenylethane-1-d/sub 1/, (S)-(+)-1-phenylethane-1,2-d/sub 2/, (S)-(+)-1-phenylethane-1,2,2-d/sub 3/, and (S)-(+)-1-phenylethane-1,2,2,2-d/sub 4/. From these spectra the authors have been able to assign fully the aliphatic CD and CH stretching vibrations in all four molecules. Using a harmonic force field which fits the observed frequencies, they have calculated the dipole and rotational strengths of these modes on the basis of the charge flow model. These calculations show that this model underestimates the VCD intensities of these stretching modes. However, the model can be improved through the introduction of polarization terms. Generally applicable analytical expressions for such terms are derived. When applied to the phenylethanes, they lead to the correct orders of magnitude for the rotational strengths.

Abbate, S.; Havel, H.A.; Laux, L.; Pultz, V.; Moscowitz, A.

1988-06-02

381

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

382

String Vibrations  

NSDL National Science Digital Library

This site, by Andrew Davidhazy at the Rochester Institute of Technology, describes how to make interesting and artistic photographs of a vibrating string. Davidhazy explains how the string is vibrated, how the string is lit, and even the exposure time and the effect it has on the resulting image. Four images of the vibrating string are included.

Davidhazy, Andrew

383

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

384

HARMONIC CYCLOTRON HEATING IN THE TOROIDAL OCTUPOLE  

E-print Network

HARMONIC CYCLOTRON HEATING IN THE TOROIDAL OCTUPOLE J. C. Sprott October 1976 Plasma Studies PLP without consent of the author and maj or professor. #12;-2- Previous calculations of cyclotron resonance the harmonic cyclotron heating of both electrons and ions. It is well known (see, for example, O. Eldridge

Sprott, Julien Clinton

385

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

386

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

387

Vibrational properties of semitrimer picotubes  

NASA Astrophysics Data System (ADS)

The semitrimer picotube is a ring-shaped hydrocarbon closely related to a very short (3,3) carbon nanotube. We study the vibrational properties of the semitrimer by means of Raman spectroscopy and find the structural similarity to nanotubes to be reflected also in the vibrational spectra. In particular, combining polarization-dependent Raman measurements and ab inito calculations we can identify a fully symmetric vibration corresponding to the radial breathing mode in nanotubes.

Rosenkranz, N.; Machón, M.; Herges, R.; Thomsen, C.

2008-01-01

388

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

389

A computer program to calculate zeroes, extrema, and interval integrals for the associated Legendre functions. [for estimation of bounds of truncation error in spherical harmonic expansion of geopotential  

NASA Technical Reports Server (NTRS)

A computer program is described for the calculation of the zeroes of the associated Legendre functions, Pnm, and their derivatives, for the calculation of the extrema of Pnm and also the integral between pairs of successive zeroes. The program has been run for all n,m from (0,0) to (20,20) and selected cases beyond that for n up to 40. Up to (20,20), the program (written in double precision) retains nearly full accuracy, and indications are that up to (40,40) there is still sufficient precision (4-5 decimal digits for a 54-bit mantissa) for estimation of various bounds and errors involved in geopotential modelling, the purpose for which the program was written.

Payne, M. H.

1973-01-01

390

Vibrational spectroscopic studies and Natural Bond Orbital analysis of 4,6-dichloro-2-(methylthio)pyrimidine based on density functional theory  

Microsoft Academic Search

The FT-IR and FT-Raman spectra of 4,6-dichloro-2-(methylthio)pyrimidine (DMP) have been recorded and analyzed. The optimized geometry, intramolecular hydrogen bonding, and harmonic vibrational wave numbers of DMP have been investigated with the help of B3LYP density functional theory (DFT) method supplemented with 6-31G** basis set. The infrared and Raman spectra were predicted theoretically from the calculated intensities. Natural Bond Orbital (NBO)

V. Balachandran; A. Lakshmi; A. Janaki

2011-01-01

391

Vibrational spectroscopy of resveratrol  

NASA Astrophysics Data System (ADS)

In this article the authors deal with the experimental and theoretical interpretation of the vibrational spectra of trans-resveratrol (3,5,4'-trihydroxy- trans-stilbene) of diverse beneficial biological activity. Infrared and Raman spectra of the compound were recorded; density functional calculations were carried out resulting in the optimized geometry and several properties of the molecule. Based on the calculated force constants, a normal coordinate analysis yielded the character of the vibrational modes and the assignment of the measured spectral bands.

Billes, Ferenc; Mohammed-Ziegler, Ildikó; Mikosch, Hans; Tyihák, Ern?

2007-11-01

392

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

393

Size-extensive vibrational self-consistent field method  

NASA Astrophysics Data System (ADS)

The vibrational self-consistent field (VSCF) method is a mean-field approach to solve the vibrational Schrödinger 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 partial ^4 V / partial Q_i^2 partial Q_j^2 type, where V is the electronic energy and Qi 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.

Keçeli, Murat; Hirata, So

2011-10-01

394

Energetics, structures, vibrational frequencies, vibrational absorption, vibrational circular dichroism and Raman intensities of Leuenkephalin  

Microsoft Academic Search

Here we present several low energy conformers of Leu-enkephalin (LeuE) calculated with the density functional theory using the Becke 3LYP hybrid functional and the 6-31G* basis set. The structures, conformational energies, vibrational frequencies, vibrational absorption (VA) intensities, vibrational circular dichroism (VCD) intensities and Raman scattering intensities are reported for the conformers of LeuE which are expected to be populated at

K J Jalkanen

2003-01-01

395

Coupling between plate vibration and acoustic radiation  

NASA Technical Reports Server (NTRS)

A detailed numerical investigation of the coupling between the vibration of a flexible plate and the acoustic radiation is performed. The nonlinear Euler equations are used to describe the acoustic fluid while the nonlinear plate equation is used to describe the plate vibration. Linear, nonlinear, and quasi-periodic or chaotic vibrations and the resultant acoustic radiation are analyzed. We find that for the linear plate response, acoustic coupling is negligible. However, for the nonlinear and chaotic responses, acoustic coupling has a significant effect on the vibration level as the loading increases. The radiated pressure from a plate undergoing nonlinear or chaotic vibrations is found to propagate nonlinearly into the far-field. However, the nonlinearity due to wave propagation is much weaker than that due to the plate vibrations. As the acoustic wave propagates into the far-field, the relative difference in level between the fundamental and its harmonics and subharmonics decreases with distance.

Frendi, Abdelkader; Maestrello, Lucio; Bayliss, Alvin

1992-01-01

396

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

397

Ab initio vibrational analysis of trans- and gauche-2,3-dimethylbuta-1,3-diene  

NASA Astrophysics Data System (ADS)

The harmonic force fields of the s- trans( anti) and gauche conformers of 2,3-dimethylbuta-1,3-diene have been calculated ab initio at the RHF/6-31G//RHF/6-31G level. These force fields have been further refined using scale factors transferred from analogous calculations at the RHF/6-31G level for s- trans-buta-1,3-diene and ethane. A complete assignment of the experimental vibrational frequencies is given. Regularities in the vibrational spectra of the stable conformers of buta-1,3-diene, isoprene (2-methylbuta-1,3-diene) and 2,3-dimethylbuta-1,3-diene are discussed.

Bock, Charles W.; Panchenko, Yurii N.

1990-04-01

398

Experimental and DFT studies on the vibrational, electronic spectra and NBO analysis of thiamethoxam  

NASA Astrophysics Data System (ADS)

Vibrational and electronic spectral measurements were performed for 3-(2-chloro-1,3-thiazol-5-ylmethyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene(nitro) amine (thiamethoxam). Optimized geometrical structure and harmonic vibrational frequencies were calculated with ab initio RHF and DFT (B3LYP, CAMB3LYP, M06 and PBE1PBE) methods with 6-311++G (d, p) basis set. Complete assignments of the observed spectra were proposed. The absorption spectra of the compound were computed in gas-phase using TD-B3LYP/6-311++G (d, p) approach and H2O solution using PCM-TD-B3LYP/6-311++G (d, p) approach. The calculated results matched well with the experimental values. Temperature dependence of thermodynamic parameters in the range of 100-1000 K were determined. The bond orbital occupancies, contribution from parent natural bond orbital (NBO), the natural atomic hybrids was discussed.

Zhang, Fang; Zhang, Yu; Ni, Haiwei; Ma, Kuirong; Li, Rongqing

2014-01-01

399

VIBRATIONALLY EXCITED C{sub 6}H  

SciTech Connect

Rotational spectra of the linear carbon chain radical C{sub 6}H in two low-lying excited vibrational states were observed both at millimeter wavelengths in a low-pressure glow discharge and at centimeter wavelengths in a supersonic molecular beam. Two series of harmonically related lines with rotational constants within 0.3% of the {sup 2{Pi}} ground state were assigned to the {sup 2{Sigma}} and {sup 2{Delta}} vibronic components of an excited bending vibrational level. Measurements of the intensities of the lines in the glow discharge indicate that the {sup 2{Sigma}} component lies very close to ground, but the {sup 2{Delta}} component is much higher in energy. The standard Hamiltonian for an isolated {sup 2{Delta}} state with five spectroscopic constants reproduces the observed rotational spectrum, but several high-order distortion terms in the spin-rotation interaction are needed to reproduce the spectrum of the {sup 2{Sigma}} component in C{sub 6}H and C{sub 6}D. The derived spectroscopic constants allow astronomers to calculate the rotational spectra of the {sup 2{Sigma}} and {sup 2{Delta}} states up to 260 GHz to within 0.1 km s{sup -1} or better in equivalent radial velocity.

Gottlieb, C. A.; McCarthy, M. C.; Thaddeus, P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2010-08-15

400

Noninvasive 3D pressure calculation from PC-MRI via non-iterative harmonics-based orthogonal projection: constant flow experiment.  

PubMed

Use of phase-contrast (PC) MRI in assessment of hemodynamics has significant clinical importance. In this paper we develop a novel approach to determination of hemodynamic pressures. 3D gradients of pressure obtained from Navier-Stokes equation are expanded into a series of orthogonal basis functions, and are subsequently projected onto an integrable subspace. Before the projection step however, a scheme is devised to eliminate the discontinuity at the vessel and image boundaries. In terms of the computation time, the proposed approach significantly improves on previous iterative methods for pressure calculations. The method has been validated using computational fluid dynamic simulations and in-vitro MRI studies of stenotic flows. PMID:24110706

Negahdar, M J; Kadbi, Mo; Cha, J; Cebral, J; Amini, A

2013-01-01

401

Resonance vibrations of aircraft propellers  

NASA Technical Reports Server (NTRS)

On the basis of the consideration of various possible kinds of propeller vibrations, the resonance vibrations caused by unequal impacts of the propeller blades appear to be the most important. Their theoretical investigation is made by separate analysis of torsional and bending vibrations. This method is justified by the very great difference in the two natural frequencies of aircraft propeller blades. The calculated data are illustrated by practical examples. Thereby the observed vibration phenomenon in the given examples is explained by a bending resonance, for which the bending frequency of the propeller is equal to twice the revolution speed.

Liebers, Fritz

1932-01-01

402

Experimental and DFT studies on the vibrational and electronic spectra of 2-(1H-Imidazo [4,5-ƒ][1,10]phenanthrolin-2-yl)phenol  

NASA Astrophysics Data System (ADS)

The compound 2-(1H-Imidazo [4,5-ƒ][1,10] phenanthrolin-2-yl) phenol (IPP) was synthesized, followed by structure determination by X-ray diffraction, the results of which agree well with the calculated optimized, lowest energy geometrical structure. Vibrational information was obtained by FT-IR and Raman spectroscopy which also agree well with calculations (of harmonic vibration frequencies). The calculations were carried out with density functional theory B3LYP methods using 6-311G** and LANL2DZ basis sets. Absorption UV-Vis experiments of IPP in CH3OH solution reveal three maximum peaks at 237.0, 274.0 and 335.0 nm, which are in agreement with calculated electronic transitions using TD-B3LYP/6-311G** in CH3OH solution, and agree to a lesser extent with gas-phase calculations.

Tang, Tingting; Tang, Guodong; Kou, ShanShan; Zhao, Jianyin; Culnane, Lance F.; Zhang, Yu

2014-01-01

403

Experimental and DFT studies on the vibrational and electronic spectra of 2-(4,5-phenyl-1H-imidazole-2-yl)-phenol  

NASA Astrophysics Data System (ADS)

The compound 2-(4,5-phenyl-1H-imidazole-2-yl-phenol (PIP) was synthesized, followed by structure determination by X-ray diffraction, the results of which agree well with the calculated optimized, lowest energy geometrical structure. Vibrational information was obtained by FT-IR and Raman spectroscopy which also agree well with calculations (of harmonic vibration frequencies). The calculations were carried out with density functional theory B3LYP methods using 6-311++G** and LANL2DZ basis sets. Absorption UV-Vis experiments of PIP in CH3CH2OH solution reveal three maximum peaks at 245, 292 and 317 nm, which are in agreement with calculated electronic transitions using TD-B3LYP/6-311++G** in CH3CH2OH solution, and agree to the gas-phase calculations.

Ye, Yunfeng; Tang, Guodong; Tang, Tingting; Culnane, Lance F.; Zhao, Jianyin; Zhang, Yu

2015-02-01

404

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

PubMed

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. PMID:25448957

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

2015-02-01

405

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

406

PREFACE: Vibrations at surfaces Vibrations at surfaces  

NASA Astrophysics Data System (ADS)

This special issue is dedicated to the phenomenon of vibrations at surfaces—a topic that was indispensible a couple of decades ago, since it was one of the few phenomena capable of revealing the nature of binding at solid surfaces. For clean surfaces, the frequencies of modes with characteristic displacement patterns revealed how surface geometry, as well as the nature of binding between atoms in the surface layers, could be different from that in the bulk solid. Dispersion of the surface phonons provided further measures of interatomic interactions. For chemisorbed molecules on surfaces, frequencies and dispersion of the vibrational modes were also critical for determining adsorption sites. In other words, vibrations at surfaces served as a reliable means of extracting information about surface structure, chemisorption and overlayer formation. Experimental techniques, such as electron energy loss spectroscopy and helium-atom-surface scattering, coupled with infra-red spectroscopy, were continually refined and their resolutions enhanced to capture subtleties in the dynamics of atoms and molecules at surfaces. Theoretical methods, whether based on empirical and semi-empirical interatomic potential or on ab initio electronic structure calculations, helped decipher experimental observations and provide deeper insights into the nature of the bond between atoms and molecules in regions of reduced symmetry, as encountered on solid surfaces. Vibrations at surfaces were thus an integral part of the set of phenomena that characterized surface science. Dedicated workshops and conferences were held to explore the variety of interesting and puzzling features revealed in experimental and theoretical investigations of surface vibrational modes and their dispersion. One such conference, Vibrations at Surfaces, first organized by Harald Ibach in Juelich in 1980, continues to this day. The 13th International Conference on Vibrations at Surfaces was held at the University of Central Florida, Orlando, in March 2010. Several speakers at this meeting were invited to contribute to the special section in this issue. As is clear from the articles in this special section, the phenomenon of vibrations at surfaces continues to be a dynamic field of investigation. In fact, there is a resurgence of effort because the insights provided by surface dynamics are still fundamental to the development of an understanding of the microscopic factors that control surface structure formation, diffusion, reaction and structural stability. Examination of dynamics at surfaces thus complements and supplements the wealth of information that is obtained from real-space techniques such as scanning tunneling microscopy. Vibrational dynamics is, of course, not limited to surfaces. Surfaces are important since they provide immediate deviation from the bulk. They display how lack of symmetry can lead to new structures, new local atomic environments and new types of dynamical modes. Nanoparticles, large molecules and nanostructures of all types, in all kinds of local environments, provide further examples of regions of reduced symmetry and coordination, and hence display characteristic vibrational modes. Given the tremendous advance in the synthesis of a variety of nanostructures whose functionalization would pave the way for nanotechnology, there is even greater need to engage in experimental and theoretical techniques that help extract their vibrational dynamics. Such knowledge would enable a more complete understanding and characterization of these nanoscale systems than would otherwise be the case. The papers presented here provide excellent examples of the kind of information that is revealed by vibrations at surfaces. Vibrations at surface contents Poisoning and non-poisoning oxygen on Cu(410)L Vattuone, V Venugopal, T Kravchuk, M Smerieri, L Savio and M Rocca Modifying protein adsorption by layers of glutathione pre-adsorbed on Au(111)Anne Vallée, Vincent Humblot, Christophe Méthivier, Paul Dumas and Claire-Marie Pradier Relating temperature dependence of atom

Rahman, Talat S.

2011-12-01

407

Lagrangian approach to molecular vibrational Raman intensities using time-dependent hybrid density functional theory.  

PubMed

The authors propose a new route to vibrational Raman intensities based on analytical derivatives of a fully variational polarizability Lagrangian. The Lagrangian is constructed to recover the negative frequency-dependent polarizability of time-dependent Hartree-Fock or adiabatic (hybrid) density functional theory at its stationary point. By virtue of the variational principle, first-order polarizability derivatives can be computed without using derivative molecular orbital coefficients. As a result, the intensities of all Raman-active modes within the double harmonic approximation are obtained at approximately the same cost as the frequency-dependent polarizability itself. This corresponds to a reduction of the scaling of computational expense by one power of the system size compared to a force constant calculation and to previous implementations. Since the Raman intensity calculation is independent of the harmonic force constant calculation more, computationally demanding density functionals or basis sets may be used to compute the polarizability gradient without much affecting the total time required to compute a Raman spectrum. As illustrated for fullerene C60, the present approach considerably