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1

Harmonic Vibrations  

Microsoft Academic Search

In this chapter vibrations shall be investigated, and in particular an oscillator\\u000a \\u000a \\u000a \\u000a • \\u000a \\u000a \\u000a Without and with damping\\u000a \\u000a \\u000a \\u000a \\u000a • \\u000a \\u000a \\u000a Without and with coupling to other oscillators, as well as\\u000a \\u000a \\u000a \\u000a \\u000a • \\u000a \\u000a \\u000a Without and with external force\\u000a \\u000a \\u000a \\u000a \\u000a \\u000a \\u000a \\u000a In the context of the external force we shall encounter a very simple case of a Green function, which plays an important role\\u000a in statistical mechanics.

Dieter Strauch

2

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

PubMed

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 using 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 in the energy calculations amount to 36N - 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 (water dimer and trimer) are presented. In all cases the frequencies based on internal coordinates differ on average by <1 cm(-1) from those obtained from Cartesian coordinates. PMID:23406376

Miliordos, Evangelos; Xantheas, Sotiris S

2013-08-15

3

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

4

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

5

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

6

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

7

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

8

A numerical model for calculating vibration due to a harmonic moving load on a floating-slab track with discontinuous slabs in an underground railway tunnel  

NASA Astrophysics Data System (ADS)

This paper presents a new method for modelling floating-slab tracks with discontinuous slabs in underground railway tunnels. The track is subjected to a harmonic load moving with a constant velocity. The model consists of two sub-models. The first is an infinite track with periodic double-beam unit formulated as a periodic infinite structure. The second is modelled with a new version of the Pipe-in-Pipe (PiP) model that accounts for a tunnel wall embedded in a half-space. The two sub-models are coupled by writing the force transmitted from the track to the tunnel as a continuous function using Fourier series representation and satisfying the compatibility condition. The displacements at the free surface are calculated for a track with discontinuous slab and compared with those of a track with continuous slab. The results show that the far-field vibration can be significantly increased due to resonance frequencies of slabs for tracks with discontinuous slabs.

Hussein, M. F. M.; Hunt, H. E. M.

2009-03-01

9

Temperature-dependent vibrational heterogeneities in harmonic glasses  

NASA Astrophysics Data System (ADS)

Numerical simulation is employed to study dynamical heterogeneities in model monoatomic harmonic glasses, whose atoms interact trough the Lennard-Jones potential. Soft and hard vibrational heterogeneities are observed, and a temperature effect on these heterogeneities is found. A method is proposed to evaluate the size of the heterogeneities.

Rossi, B.; Viliani, G.; Duval, E.; Angelani, L.; Garber, W.

2005-07-01

10

Harmonic Motion Detection in a Vibrating Scattering Medium  

PubMed Central

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

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

2008-01-01

11

One atomic beam as a detector of classical harmonic vibrations with micro amplitudes and low frequencies  

NASA Astrophysics Data System (ADS)

We propose a simplest detector of harmonic vibrations with micro amplitudes and low frequencies, i.e. a detector consisting of one atomic beam. Here, the atomic beam is induced by a plane harmonic wave and has classical collective harmonic vibrations, whose vibrant directions are perpendicular to the wave vectors of the atomic beam. Compared with a detector consisting of an atomic Mach-Zehnder interferometer, the new detector has two advantages: (1) it is suitable for the detection of harmonic vibrations induced either by a longitudinal plane harmonic wave or by using a transverse plane harmonic wave: (2) the quantum noise fluctuation of the atomic beam is exactly zero. We present the principle for detecting classical harmonic vibrations with micro amplitudes and low frequencies by using the new detector. The frequency of a classical harmonic vibration with a micro amplitude can be evaluated by measuring the variations in the mean numbers of atoms arriving at the atomic detector.

Huang, Yong-Yi

2014-03-01

12

Calculating Ro-Vibrational Spectra of Van Der Waals Molecules  

NASA Astrophysics Data System (ADS)

Van der Waals molecules are loosely bound and strongly coupled and their spectroscopy can therefore not be understood with a rigid rotor + harmonic oscillator model. Useful insight can be obtained by numerically solving the ro-vibrational Schroedinger equation using a basis set. The most obvious impediment is the size of the basis required to obtain converged results. Nonetheless, by using an iterative eigensolver and exploiting the structure of quadrature approximations for potential matrix elements, it is possible to do calculations for many molecules of interest. I shall discuss how the choice of the vibrational coordinates and the molecule-fixed axis system influence the calculation of ro-vibrational spectra of Van der Waals molecules and present new results for (NNO)_2, H_2-H_2O, and SF_6-He_2.

Wang, Xiaogang; Carrington, Tucker, Jr.

2010-06-01

13

A study on stress and vibration analysis of a steel and hybrid flexspline for harmonic drive  

Microsoft Academic Search

The conventional speed reducer uses the concept of rigid bodies, but the harmonic drive is operated by the elastic theory. As for this, harmonic drive shows different characteristics in operation principles and analysis compared to the conventional ones. Flexspline with components of harmonic drive can generate repeated vibration by the wave generator. Thus flexspline should have a good vibration characteristic.

Han Su Jeon; Se Hoon Oh

1999-01-01

14

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

NASA Astrophysics Data System (ADS)

The vibrational spectroscopy and relaxation of an anharmonic oscillator coupled to a harmonic bath are examined to assess the applicability of the time correlation function (TCF), the response function, and the semiclassical frequency modulation (SFM) model to the calculation of infrared (IR) spectra. These three approaches are often used in connection with the molecular dynamics simulations but have not been compared in detail. We also analyze the vibrational energy relaxation (VER), which determines the line shape and is itself a pivotal process in energy transport. The IR spectra and VER are calculated using the generalized Langevin equation (GLE), the Gaussian wavepacket (GWP) method, and the quantum master equation (QME). By calculating the vibrational frequency TCF, a detailed analysis of the frequency fluctuation and correlation time of the model is provided. The peak amplitude and width in the IR spectra calculated by the GLE with the harmonic quantum correction are shown to agree well with those by the QME though the vibrational frequency is generally overestimated. The GWP method improves the peak position by considering the zero-point energy and the anharmonicity although the red-shift slightly overshoots the QME reference. The GWP also yields an extra peak in the higher-frequency region than the fundamental transition arising from the difference frequency of the center and width oscillations of a wavepacket. The SFM approach underestimates the peak amplitude of the IR spectra but well reproduces the peak width. Further, the dependence of the VER rate on the strength of an excitation pulse is discussed.

Joutsuka, Tatsuya; Ando, Koji

2011-05-01

15

Vibrational modes in thymine molecule from an ab initio MO calculation  

Microsoft Academic Search

Ab initio self-consistent field molecular orbital (SCF MO) calculations have been made of the thymine molecule for the equilibrium geometry, harmonic force constants, vibrational frequencies, vibrational modes, infrared intensities, and Raman intensities. The results have been correlated with the observed Raman and infrared spectra of thymine crystalline powder.

Misako Aida; Motohisa Kaneko; Michel Dupuis; Toyotoshi Ueda; Koichi Ushizawa; Gen Ito; Akiko Kumakura; Masamichi Tsuboi

1997-01-01

16

Variational calculations of vibrational properties of ozone  

NASA Technical Reports Server (NTRS)

A variational method is used to obtain vibrational-rotational properties for ozone from an experimental quartic force field. Band positions, average structures, matrix elements for calculating infrared intensities, and effective rotational constants are reported for (O-16)3 and its O-18 isotopic species. Also, the degree to which the vibrational energies and properties are converged is investigated as a function of the basis set parameters and basis set size, and of the method of obtaining the Hamiltonian matrix elements. A convenient procedure for assigning the vibrational states is developed for variational vibrational wavefunction expansions.

Carney, G. D.; Curtiss, L. A.; Langhoff, S. R.

1977-01-01

17

Calculating Buckling And Vibrations Of Lattice Structures  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

18

On the Adaptation of Excitation Forces in the Harmonic Vibration Test.  

National Technical Information Service (NTIS)

Aspects of vibration mechanics and the theoretical background of the harmonic vibration test for structures and the fundamental problem of isolating a mode by adaptation of excitation forces for the precise determination of modal characteristics are discu...

1975-01-01

19

Calculation of the vibrational spectra of cytosine derivatives by the CNDO/2 force method. Part II. Planar vibrations of 5-fluorocytosine  

NASA Astrophysics Data System (ADS)

Calculations of harmonic force constants by the CNDO/2 method with Pulay's empirical correction have been performed for 5-fluorocytosine in the amino—enol tautomeric form. Vibrational frequencies and normal modes for in-plane vibrations were found. On the basis of the calculations, assignments of infrared absorption bands of the low temperature nitrogen matrix spectrum of 5-fluorocytosine to normal modes of vibration are proposed. Intensities of fundamental absorptions were also calculated.

Kuczera, Krzysztof; Szczesniak, Marian; Szczepaniak, Krystyna

1988-02-01

20

Harmonic Torque Calculation of Induction Motors Using Electromagnetic Field Analysis  

NASA Astrophysics Data System (ADS)

In this paper, we investigate effects of harmonic electromagnetic field to torque characteristics of induction motors from both side of experiment and electromagnetic field analysis. The characteristics of two kinds of the aluminum cage three-phase induction motors are measured and calculated. One is with the closed rotor slots. The other is semi-closed. In the experiment, the negative torque at synchronous speed is measured by driving the induction motor by the synchronous permanent magnet motor. The total torque at load condition is also measured by the torque detector. In the analysis, the harmonic magnetic fields, the harmonic losses and the harmonic torques at each time and space harmonic order are calculated using the nonlinear time-stepping finite element method to clarify the mechanism of the harmonic torque generation. The measured and the calculated results agree well. It is clarified that the negative torque caused by the slot harmonics at the rated load condition is not negligible and that the negative torque is mainly generated by the harmonic core losses.

Yamazaki, Katsumi; Haruishi, Yoshihisa; Ara, Takahiro

21

An effective scaling frequency factor method for scaling of harmonic vibrational frequencies: Application to 1,2,4-triazole derivatives  

Microsoft Academic Search

Scaling of harmonic frequencies of a molecule is one of the methods of improving the agreement between the calculated from a quadratic force field and experimental vibrational spectrum. An application of the recently proposed effective scaling frequency factor (ESFF) method to the complicated 1,2,4-triazole derivatives is presented. The calculations are based on the DFT\\/B3LYP\\/6-311G** quadratic force fields. It is shown

Piotr Borowski; Karol Pilorz; Monika Pitucha

2010-01-01

22

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

23

Vibrational modes in a two-dimensional aperiodic harmonic lattice.  

PubMed

We study the nature of collective excitations in classical harmonic lattices with aperiodic and pseudo-random mass distributions. Using a matrix recursive reformulation of the mass displacement equation, we compute the localization length within the band of allowed frequencies. Our numerical calculations indicate that, for aperiodic arrays of masses, a new phase of extended states appears in this model. Solving numerically the Hamilton equations for momentum and displacement along the chain, we compute the spreading of an initially localized energy excitation. We find that for sufficient aperiodicity, there is a ballistic propagation of the energy pulse. PMID:21403325

de Moura, F A B F

2010-11-01

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

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

26

Piezoelectric MEMS energy harvesting systems driven by harmonic and random vibrations.  

PubMed

Switching power conditioning techniques are known to greatly enhance the performance of linear piezoelectric energy harvesters subject to harmonic vibrations. With such circuits, little is known about the effect of mechanical stoppers that limit the motion or about waveforms other than harmonic vibrations. This work presents SPICE simulations of piezoelectric micro energy harvester systems that differ in choice of power conditioning circuits and stopper models. We consider in detail both harmonic and random vibrations. The nonlinear switching conversion circuitry performs better than simple passive circuitry, especially when mechanical stoppers are in effect. Stopper loss is important under broadband vibrations. Stoppers limit the output power for sinusoidal excitations, but result in the same output power whether the stoppers are lossy or not. When the mechanical stoppers are hit by the proof mass during high-amplitude vibrations, nonlinear effects such as saturation and jumps are present. PMID:20378453

Blystad, Lars-Cyril; Halvorsen, Einar; Husa, Svein

2010-04-01

27

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

28

An ab initio study of the harmonic force field and vibrational frequencies of thionylimide: Basis set and electron correlation effects  

Microsoft Academic Search

Basis set and electron correlation effects on the geometry and harmonic force field of thionylimide (HNSO) are investigated in detail. d functions on S are essential in describing the bonding in this compound. The calculated Hartree–Fock vibrational frequencies are about 15% too high. Inclusion of electron correlation at the second and third order Moller–Plesset perturbation levels (MP2 and MP3) gives

Krishnan Raghavachari

1982-01-01

29

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

30

Vibrational and thermodynamic properties of Ni 3 S 2 polymorphs from first-principles calculations  

Microsoft Academic Search

We have calculated the compressional, vibrational, and thermodynamic properties of Ni3S2 heazlewoodite and the high-pressure orthorhombic phase (with Cmcm symmetry) using the generalized gradient approximation\\u000a to the density functional theory in conjunction with the quasi-harmonic approximation. The predicted Raman frequencies of\\u000a heazlewoodite are in good agreement with room-temperature measurements. The calculated thermodynamic properties of heazlewoodite\\u000a at room conditions agree very

Yonggang G. Yu; Nancy L. Ross

2011-01-01

31

High-order harmonic transient grating spectroscopy of SF6 molecular vibrations  

NASA Astrophysics Data System (ADS)

Strong field transient grating spectroscopy has shown to be a very versatile tool in time-resolved molecular spectroscopy. Here we use this technique to investigate the high-order harmonic generation from SF6 molecules vibrationally excited by impulsive stimulated Raman scattering. Transient grating spectroscopy enables us to reveal clear modulations of the harmonic emission. This heterodyne detection shows that the harmonic emission generated between 14 and 26 eV is mainly sensitive to two among the three active Raman modes in SF6, i.e. the strongest and fully symmetric ?1-A1g mode (774 cm?1, 43 fs) and the slowest mode ?5-T2g (524 cm?1, 63 fs). A time-frequency analysis of the harmonic emission reveals additional dynamics: the strength and central frequency of the ?1 mode oscillate with a frequency of 52 cm?1 (640 fs). This could be a signature of the vibration of dimers in the generating medium. Harmonic 11 shows a remarkable behaviour, oscillating in the opposite phase, both on the fast (774 cm?1) and slow (52 cm?1) timescales, which indicates a strong modulation of the recombination matrix element as a function of the nuclear geometry. These results demonstrate that the high sensitivity of high-order harmonic generation to molecular vibrations, associated to the high sensitivity of transient grating spectroscopy, make their combination a unique tool to probe vibrational dynamics.

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

2014-06-01

32

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

NASA Technical Reports Server (NTRS)

The design, implementation, and flight test results of higher harmonic blade feathering for vibration reduction on the OH-6A helicopter are described. The higher harmonic control (HHC) system superimposes fourth harmonic inputs upon the stationary swashplate. These inputs are transformed into 3P, 4P and 5P blade feathering angles. This results in modified blade loads and reduced fuselage vibrations. The primary elements of this adaptive vibration suppression system are: (1) acceleration transducers sensing the vibratory response of the fuselage; (2) a higher harmonic blade pitch actuator system; (3) a flightworthy microcomputer, incorporating the algorithm for reducing vibrations, and (4) a signal conditioning system, interfacing between the sensors, the microcomputer and the HHC actuators. The program consisted of three distinct phases. First, the HHC system was designed and implemented on the MDHC OH-6A helicopter. Then, the open loop, or manual controlled, flight tests were performed, and finally, the closed loop adaptive control system was tested. In 1983, one portion of the closed loop testing was performed, and in 1984, additional closed loop tests were conducted with improved software. With the HHC system engaged, the 4P pilot seat vibration levels were significantly lower than the baseline ON-6A levels. Moreover, the system did not adversely affect blade loads or helicopter performance. In conclusion, this successful proof of concept project demonstrated HHC to be a viable vibration suppression mechanism.

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

1986-01-01

33

Power System Harmonics and Unbalance Distribution Calculation Based on Measurement  

Microsoft Academic Search

The modeling of harmonic source based on harmonic measurement is put forward for the first time. Three-phase fundamental and harmonic models of the whole power system are built in the paper. Then, the power system harmonics penetration (PSHP) software package is developed on VC++ circumstance. Zhengzhou, Luoyang and Sanmengxia electric power system in Henan grid are studied, and the harmonics

Xilu Zhang; Junyong Wu; Yangyu Hu; Hongjun Fu; Luyu Ji; Honglei Song

2011-01-01

34

Rigid mode and harmonic response analysis of three-body vibrating screen  

Microsoft Academic Search

By using the ADAMS, the dynamic parameters of three-body vibrating screen are extracted, and the simple finite element model is established on the basis of parameters in ANSYS. The amplitude-frequency curve and phase-frequency curve is obtained by using the harmonic analysis. According to the error between the simulated amplitude of the vibrating screen and the actual magnitude, the correctness of

Chuanguang Ding; Fangzhen Song; Bo Song

2011-01-01

35

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

36

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

37

Ensemble approach to coherence between two scalar harmonic light vibrations and the phase difference  

SciTech Connect

We develop an approach to coherence between two scalar harmonic light vibrations derived from the ensemble interpretation of statistical optics. Coherence is presented as a statistical variable itself that turns out to be the phase difference between the two vibrations. This provides a natural and simple extension of second-order coherence to cover more complicated situations. This includes in a single formalism both classic and quantum light states, allowing the most accurate interferometric measurements, even if they are incoherent according to the standard second-order approach.

Luis, Alfredo [Departamento de Optica, Facultad de Ciencias Fisicas, Universidad Complutense, 28040 Madrid (Spain)

2009-05-15

38

Calculating Transient Vibrations Of Coupled Substructures  

NASA Technical Reports Server (NTRS)

Finite-element, numerical-integration method for estimating transient vibrational response of structure composed of coupled substructures entails less computation. Responses of substructures to external forces and to forces of interaction between substructures computed. Equations of motion of each substructure solved independently. Applicable to any number and configuration of linearly responding substructures and to both determinate and indeterminate boundary conditions at interfaces between substructures. Also applicable to changing interface boundary conditions.

Admire, J. R.; Brunty, J. A.

1991-01-01

39

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

40

Suppressing harmonic vibrations of a miniature cryogenic cooler using an adaptive tunable vibration absorber based on magneto-rheological elastomers.  

PubMed

This paper presents dynamic performances of an adaptive tunable vibration absorber (TVA) designed to suppress the main harmonic disturbance of a miniature linear cryogenic cooler, which is being used in space applications such as an observation satellite. The adaptive TVA employs a magneto-rheological elastomer (MRE) for a variable stiffness element. This study first investigates the shear modulus change of MRE samples with respect to the magnetic flux density, which varies through the alignment of particle chains. The MRE with the maximal shear modulus change is mounted for the TVA on a prototype cooler, which emulates the characteristics of a miniature cryogenic cooler. Using the test setup, a series of vibration tests are performed to evaluate the performance and efficacy of the MRE TVA and its re-tuning ability. The experimental results show that the MRE TVA is able to robustly suppress the vibration of the cooler even when the frequency of resonant vibration is changed up to 87% from its initial frequency. PMID:21456785

Kim, Y-K; Koo, J H; Kim, K-S; Kim, S H

2011-03-01

41

Ab initio molecular orbital calculations of the vibrational frequencies of XY4/sup -n/ anions  

NASA Astrophysics Data System (ADS)

The vibrational frequencies of a seris of XY4/sup -n/ anions (BeF4(-2), BF4(-), AlF4(-), MgCl4(-2), and AlCl4(-)) have been calculated by ab initio molecular orbital theory using the 3-21G and 6-31G* basis sets. The predicted harmonic frequencies are for the most part in good agreement with the observed frequencies of these anions in molten alkali halide mixtures. At the 3-21G basis set level the average difference between the observed and predicted frequencies is 12% while at the 6-31G* basis set level the average difference is 6%. Calculations of this type may be helpful in predicting the vibrational frequencies of other anions in molten salts.

Curtiss, L. A.; Nichols, R.

42

Density functional theory calculations on the molecular structures and vibration spectra of platinum(II) antitumor drugs  

NASA Astrophysics Data System (ADS)

A comparison of six density functional theory (DFT) methods and six basis sets for predicting the molecular structures and vibration spectra of cisplatin is reported. The theoretical results are discussed and compared with the experimental data. It is remarkable that LSDA/SDD level is clearly superior to all the remaining density functional methods (including mPW1PW) in predicting the structures of cisplatin. Mean deviation between the calculated harmonic and observed fundamental vibration frequencies for each method is also calculated. The results indicate that PBE1PBE/SDD is the best method to predict all frequencies on average for cisplatin molecule in DFT methods.

Gao, Hongwei; Xia, FengYi; Huang, ChangJiang; Lin, Kuangfei

2011-04-01

43

Harmonic-resonator-based triboelectric nanogenerator as a sustainable power source and a self-powered active vibration sensor.  

PubMed

A harmonic-resonator-based triboelectric nanogenerator (TENG) is presented as a sustainable power source and an active vibration sensor. It can effectively respond to vibration frequencies ranging from 2 to 200 Hz with a considerably wide working bandwidth of 13.4 Hz. This work not only presents a new principle in the field of vibration energy harvesting but also greatly expands the applicability of TENGs. PMID:23999798

Chen, Jun; Zhu, Guang; Yang, Weiqing; Jing, Qingshen; Bai, Peng; Yang, Ya; Hou, Te-Chien; Wang, Zhong Lin

2013-11-13

44

Revised vibrational band assignments for the experimental IR and Raman spectra of 2,3,4-trifluorobenzonitrile based on ab initio, DFT and normal coordinate calculations  

Microsoft Academic Search

In the present study, a systematic vibrational spectroscopic investigation for the experimental IR and Raman spectra of 2,3,4-trifluorobenzonitrile (TFB), aided by electronic structure calculations has been carried out. The electronic structure calculations –ab initio (RHF) and hybrid density functional methods (B3LYP) – have been performed with 6-31G* basis set. Molecular equilibrium geometries, electronic energies, IR intensities, harmonic vibrational frequencies, depolarization

C. S. Hiremath; G. B. Kalkoti; M. K. Aralakkanavar

2009-01-01

45

Calculation of vibrational zero-point energy  

Microsoft Academic Search

We have established an empirical formula for calculating the zero-point energy (ZPE) of organic compounds. We applied this formula to 80 molecular systems, and compared it to the AM1 semi-empirical method, in both cases with satisfactory results. We also observed that the sum ZPE+H(T)?H(0) and the empirically derived ZPE(empirical) are related by a quasi-linear relation.

M. Rahal; M. Hilali; A. El Hammadi; M. El Mouhtadi; A. El Hajbi

2001-01-01

46

Magnetostrictive vibrations model of a three-phase transformer core and the contribution of the fifth harmonic in the grid voltage  

NASA Astrophysics Data System (ADS)

The effect of the fifth harmonic in the grid voltage (with fundamental frequency of 50 Hz) on the vibrations of a three-phase transformer core is computed, since such harmonic has the largest contribution in the European grid voltage. The computational method is a two-dimensional (2D) finite element technique. The modal vibrations under various magnetisations (viz with different fifth harmonic components) are compared with those obtained under a purely sinusoidal magnetisation and showed that the variations for the 100 Hz harmonic of the vibrations are small. However, the 200 Hz harmonic showed a significant increase when a fifth harmonic was present on the applied voltage. In fact, the presence of a fundamental component with 50 Hz frequency and a fifth harmonic on the magnetisation signal generates a 200 Hz harmonic on the magnetostriction strains (and the magnetic forces), and thus this harmonic increases significantly.

Gorji Ghalamestani, Setareh; Vandevelde, Lieven; Dirckx, Joris J. J.; Melkebeek, Jan A. A.

2014-05-01

47

Geometrical Method for the Calculation of Spherical Harmonics up to an Arbitrary Degree and Order  

NASA Astrophysics Data System (ADS)

We introduce a novel method for the computation and rotation of spherical harmonics, Legendre polynomials and associated Legendre functions without making use of recursive relations. This novel geometrical approach allows calculation of spherical harmonics without any numerical instability up to an arbitrary degree and order, i.e. up to a degree and order 1e6 and beyond. It is shown, that spherical harmonics can be treated as vectors in Hilbert hyperspace leading to the unitary hermitian rotation matrices with geometric properties.

Svehla, D.

2009-12-01

48

Fully automated microcomputer calculation of vibrational spectra  

NASA Astrophysics Data System (ADS)

A fully automated method for computing frequencies and atomic displacements of normal modes, giving synthetic infrared and Raman spectra, has been developed for use on small computers. No expertise in group theory or the mathematics of normal-mode calculation are required to use the computer program. The method takes full account of symmetry and is applicable to any crystal or molecule. Force constants can be specified in terms of any two-atom “bonds” or three-atom angles. The essential steps in the computer program are: (1) Locate all atoms in the unit cell or molecule and compute displacement vectors for each internal coordinate; (2) Convert the basis of the force constants from bonds and angles to cartesian displacements; (3) Construct the full-matrix irreducible representations of the point or factor group in question, using appropriate symmetry matrices and polynomial basis functions; (4) Derive the symmetry coordinates in terms of cartesian displacements using the projection/transfer-operator technique; (5) construct secular equations for each species with Wilson's f g method; (6) solve for frequencies and atomic motions; and (7) use simple models of infrared and Raman intensities to calculate spectra.

Dowty, Eric

1987-01-01

49

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

50

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

51

Vibrational spectroscopic studies of Isoleucine by quantum chemical calculations.  

PubMed

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

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

2014-04-24

52

Vibrational assignment of the spectral data and thermodynamic properties of 2-chloro-4-fluorobenzophenone using DFT quantum chemical calculations  

Microsoft Academic Search

The FT-Raman (3500–100cm?1) and FT-IR (4000–450cm?1) spectra of 2-chloro-4-fluorobenzophenone were recorded in the solid phase. Density functional theory calculations with B3LYP\\/6-31G (d, p) basis set was used to determine the ground state molecular geometries (bond lengths and bond angles), harmonic vibrational frequencies, infrared intensities and Raman activities of this compound. Potential energy distributions (PEDs) and normal modes, for the spectral

K. Chaitanya; C. Santhamma; B. Mark Heron; Christopher D. Gabbutt; Alicia C. Instone

2011-01-01

53

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

54

FT-IR and FT-Raman spectra, vibrational assignments, NBO analysis and DFT calculations of 2-amino-4-chlorobenzonitrile  

Microsoft Academic Search

In this work, we report a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of 2-amino-4-chlorobenzonitrile (2A4CBN). The FT-IR (400–4000cm?1) and FT-Raman spectra (50–3500cm?1) of 2A4CBN were recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of 2A4CBN in the ground state have been calculated by using the density functional B3LYP method with 6-311++G

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

2011-01-01

55

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

56

Harmonics  

NSDL National Science Digital Library

This simulation illustrates the behavior of standing waves in situation where one end fixed, both ends are fixed, and both ends are free. The simulation allows the user to examine the standing wave behavior at the fundamental frequency and when the first three harmonics are added. The user can control the amplitude of each of the harmonics and observe the resulting pattern.

Renault, Pascal

2009-01-22

57

Calculation of mechanical vibration frequencies of stiffened superconducting cavities  

SciTech Connect

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

Black, S.J.; Spalek, G.

1992-01-01

58

Calculation of mechanical vibration frequencies of stiffened superconducting cavities  

SciTech Connect

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

Black, S.J.; Spalek, G.

1992-09-01

59

Observation and calculation of vibrational circular birefringence: a new form of vibrational optical activity.  

PubMed

We report the first mid-infrared observation of vibrational circular birefringence (VCB) arising from individual chiral molecules. VCB can also be called vibrational optical rotatory dispersion (VORD) and is the Kramers-Kronig transform of vibrational circular dichroism (VCD). The method of measurement involves a simple change in the optical set-up and electronic processing of a VCD spectrometer such that the VCB spectrum appears at twice the polarization modulation frequency as a pseudo vibrational linear dichroism (VLD) spectrum. VCB spectra are also calculated with density function theory (DFT) for the first time using a commercially available program for rotational strengths where the calculated intensities are convolved with the real, dispersive part of a normalized complex Lorentzian lineshape rather than the imaginary, absorptive part, normally used for IR and VCD intensity calculations. Comparison of the measured and calculated VCB, VCD, and IR spectra of (+)-R-limonene and (-)-S-alpha-pinene show close agreement and confirm the validity of the new VCB measurements. PMID:20034018

Lombardi, Rosina A; Nafie, Laurence A

2009-01-01

60

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

SciTech Connect

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

Garrett, P. E. [Department of Physics, University of Guelph, Guelph, Ontario, N1G2W1 (Canada); TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, V6T2A3 (Canada); Green, K. L.; Bangay, J.; Varela, A. Diaz; Sumithrarachchi, C. S.; Bandyopadhyay, D. S.; Bianco, L.; Demand, G. A.; Finlay, P.; Grinyer, G. F.; Leach, K. G.; Phillips, A. A.; Schumaker, M. A.; Svensson, C. E.; Wong, J. [Department of Physics, University of Guelph, Guelph, Ontario, N1G2W1 (Canada); Austin, R. A. E.; Colosimo, S. [Department of Astronomy and Physics, Saint Mary's University, Halifax, Nova Scotia, B3H3C3 (Canada); Ball, G. C.; Garnsworthy, A. B.; Hackman, G. [TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, V6T2A3 (Canada)

2011-10-28

61

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

62

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

63

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)] [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)] [Computational Physics Group, AWE Aldermaston, Berkshire (United Kingdom)

2013-07-01

64

ATOMIC AND MOLECULAR PHYSICS: Investigation of analytical potential energy function, harmonic frequency and vibrational levels for the X2?+ and A2 states of CN radical  

NASA Astrophysics Data System (ADS)

This paper calculates the equilibrium structure and the potential energy functions of the ground state (X2?+) and the low lying excited electronic state (A2II) of CN radical are calculated by using CASSCF method. The potential energy curves are obtained by a least square fitting to the modified Murrell-Sorbie function. On the basis of physical theory of potential energy function, harmonic frequency (?e) and other spectroscopic constants (?e?e, ?e and ?e) are calculated by employing the Rydberg-Klein-Rees method. The theoretical calculation results are in excellent agreement with the experimental and other complicated theoretical calculation data. In addition, the eigenvalues of vibrational levels have been calculated by solving the radial one-dimensional Schrödinger equation of nuclear motion using the algebraic method based on the analytical potential energy function.

Wang, Jian-Kun; Wu, Zhen-Sen

2008-08-01

65

Thermodynamic properties of CaCO 3 calcite and aragonite: A quasi-harmonic calculation  

Microsoft Academic Search

A quasi-harmonic model has been used to simulate the thermodynamic behaviour of the CaCO3 polymorphs, by equilibrating their crystal structures as a function of temperature so as to balance the sum of inner static and thermal pressures against the applied external pressure. The vibrational frequencies and elastic properties needed have been computed using interatomic potentials based on two-body Born-type functions,

M. Catti; A. Pavese; G. D. Price

1993-01-01

66

FT-IR and FT-Raman spectra, vibrational assignments, NBO analysis and DFT calculations of 2-amino-4-chlorobenzonitrile  

NASA Astrophysics Data System (ADS)

In this work, we report a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of 2-amino-4-chlorobenzonitrile (2A4CBN). The FT-IR (400-4000 cm -1) and FT-Raman spectra (50-3500 cm -1) of 2A4CBN were recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of 2A4CBN in the ground state have been calculated by using the density functional B3LYP method with 6-311++G (d,p) as higher basis set. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) result complements with the experimental findings. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Finally the calculation results were applied to simulate infrared and Raman spectra of the title compound which show good agreement with observed spectra.

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

2011-01-01

67

Calculations of circular intensity differences in electric-field-induced second harmonic generation  

NASA Astrophysics Data System (ADS)

Ab initio calculations of electric-field induced second-harmonic generation for chiral molecules are presented. The calculations employ cubic response theory and take into account electric-dipole, electric-quadrupole and magnetic-dipole interactions, which result in an intensity dependence on the helicity of the light. The circular intensity difference is calculated for the chiral molecules twisted ethylene, trans-1,2-dimethylcyclopropane and methyloxirane. The calculated circular intensity differences are small - being of the order of 10 -4-10 -3 - but such electric-field induced second harmonic generation intensity dependencies should be experimentally detectable.

Jonsson, Dan; Luo, Yi; Ruud, Kenneth; Norman, Patrick; Ågren, Hans

1998-05-01

68

Calculation of ground vibration spectra from heavy military vehicles  

NASA Astrophysics Data System (ADS)

The demand for reliable autonomous systems capable to detect and identify heavy military vehicles becomes an important issue for UN peacekeeping forces in the current delicate political climate. A promising method of detection and identification is the one using the information extracted from ground vibration spectra generated by heavy military vehicles, often termed as their seismic signatures. This paper presents the results of the theoretical investigation of ground vibration spectra generated by heavy military vehicles, such as tanks and armed personnel carriers. A simple quarter car model is considered to identify the resulting dynamic forces applied from a vehicle to the ground. Then the obtained analytical expressions for vehicle dynamic forces are used for calculations of generated ground vibrations, predominantly Rayleigh surface waves, using Green's function method. A comparison of the obtained theoretical results with the published experimental data shows that analytical techniques based on the simplified quarter car vehicle model are capable of producing ground vibration spectra of heavy military vehicles that reproduce basic properties of experimental spectra.

Krylov, V. V.; Pickup, S.; McNuff, J.

2010-07-01

69

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

70

Rotor blade-vortex interaction noise reduction and vibration using higher harmonic control  

NASA Technical Reports Server (NTRS)

The use of higher harmonic control (HHC) of blade pitch to reduce blade-vortex interaction (BVI) noise is examined by means of a rotor acoustic test. A dynamically scaled, four-bladed, articulated rotor model was tested in a heavy gas (Freon-12) medium. Acoustic and vibration measurements were made for a large range of matched flight conditions where prescribed (open loop) HHC pitch schedules were superimposed on the normal (baseline) collective and cyclic trim pitch. A novel sound power measurement technique was developed to take advantage of the reverberance in the hard walled tunnel. Quantitative sound power results are presented for a 4/rev (4P) collective pitch HHC. By comparing the results using 4P HHC to corresponding baseline (no HHC) conditions, significant midfrequency noise reductions of 5-6 dB are found for low-speed descent conditions where BVI is most intense. For other flight conditions, noise is found to increase with the use of HHC. LF loading noise, as well as fixed and rotating frame vibration levels, show increased levels.

Brooks, Thomas F.; Booth, Earl R., Jr.

1990-01-01

71

Six-Bodies Calculations Using the Hyperspherical Harmonics Method  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

72

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

Microsoft Academic Search

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

J. Ralph Johler; Richard L. Lewis

1969-01-01

73

Calculations of vibration-rotation energy levels of HD sup +  

SciTech Connect

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

Balint-Kurti, G.G. (School of Chemistry, The University, Bristol BS81TS, England (GB)); Moss, R.E.; Sadler, I.A. (Chemistry Department, The University, Southampton SO95NH (England)); Shapiro, M. (Department of Chemical Physics, The Weizmann Institute of Science, Rehovot (Israel))

1990-05-01

74

Calculations of vibration-rotation energy levels of HD+  

NASA Astrophysics Data System (ADS)

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

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

1990-05-01

75

On the accuracy of the harmonic balance method concerning vibrations of beams with nonlinear supports  

Microsoft Academic Search

A homogeneous beam supported by a nonlinear cubic rotational spring and excited by a prescribed harmonic translational motion was analysed by the harmonic balance method. Harmonic and sub-harmonic solutions were determined as functions of frequency, excitation amplitude and material damping. The results were verified against numerical time integrations of the governing nonlinear differential equations. The numerical method was based on

P. Gudmundson

1989-01-01

76

Calculation and manipulation of the chirp rates of high-order harmonics  

SciTech Connect

We calculate the linear chirp rates of high-order harmonics in argon, generated by intense, 810 nm laser pulses, and explore the dependence of the chirp rate on harmonic order, driving laser intensity, and pulse duration. By using a time-frequency representation of the harmonic fields we can identify several different linear chirp contributions to the plateau harmonics. Our results, which are based on numerical integration of the time-dependent Schroedinger equation, are in good agreement with the adiabatic predictions of the strong field approximation for the chirp rates. Extending the theoretical analysis in the recent paper by Mauritsson et al. [Phys. Rev. A 70, 021801(R) (2004)], we also manipulate the chirp rates of the harmonics by adding a chirp to the driving pulse. We show that the chirp rate for harmonic q is given by the sum of the intrinsic chirp rate, which is determined by the new duration and peak intensity of the chirped driving pulse, and q times the external chirp rate.

Murakami, M.; Mauritsson, J.; Schafer, K.J.; Gaarde, M.B. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001 (United States); L'Huillier, A. [Department of Physics, Lund Institute of Technology, P. O. Box 118, S-22100 Lund (Sweden)

2005-01-01

77

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

78

Calculation of the Actual Tidal Fluctuations in Harmonic Analysis (Vychislenie Istinnykh Prilivnykh Kolebanii Pri Garmonicheskom Analize).  

National Technical Information Service (NTIS)

The paper discusses more accurate calculation methods of the actual tidal fluctuations of sea level and ebb-tide currents that are necessary for harmonic analysis. A new method for the filtration of tides, which differs from the method of separating wave ...

V. M. Altshuler

1968-01-01

79

Investigation of a bistable dual-stage vibration isolator under harmonic excitation  

NASA Astrophysics Data System (ADS)

This study explores the steady-state performance of a dual-stage vibration isolator, which is configured by a bistable oscillator and a linear oscillator. The potential force of the bistable stage comprises negative linear and positive cubic nonlinear stiffnesses such that the two restoring force contributions may counterbalance to minimize dynamic force transmission. By applying a first-order harmonic balance, it is predicted that the bistable dual-stage isolator may significantly outperform an equivalent pure linear dual-stage isolator. This conclusion is verified through a series of numerical investigations. Following a parametric study, design guidelines are detailed to achieve performance improvements. Then, the ‘valley’ response, which is the special phenomenon of the bistable dual-stage isolator due to the counterbalance of the negative linear and positive nonlinear potential forces, is revealed and quantitatively explained. Numerical studies demonstrate the role of initial conditions, and it is shown that the likelihood of beneficial single periodic valley and intra-well responses for isolation purposes can be increased by greater bistable stage damping. Finally, a bistable dual-stage isolator prototype is developed and tested, and the numerical and experimental results verify the theoretical predictions.

Yang, Kai; Harne, R. L.; Wang, K. W.; Huang, Hai

2014-04-01

80

An effective scaling frequency factor method for scaling of harmonic vibrational frequencies: theory and preliminary application to toluene  

Microsoft Academic Search

In this Letter, we propose a new method for scaling of harmonic vibrational frequencies named effective scaling frequency factor (ESFF) method. It uses effective scaling factors obtained through diagonal coefficients of the potential energy distribution matrix, PED, on the basis of a non-redundant natural coordinates set. The preliminary application of ESFF method at B3LYP\\/6-311G?? level to toluene in the region

Piotr Borowski; Manuel Fernández-Gómez; Maria-Paz Fernández-Liencres; Tomás Peña Ruiz

2007-01-01

81

A new method to calculate Franck-Condon factors of multidimensional harmonic oscillators including the Duschinsky effect  

NASA Astrophysics Data System (ADS)

Calculations of Franck-Condon factors are crucial for interpreting vibronic spectra of molecules and studying nonradiative processes. We have developed a new method for calculating Franck-Condon factors of multidimensional harmonic oscillators including the Duschinsky effect. Closed-form formulas of two-, three-, and four-dimensional Franck-Condon factors were derived straightforwardly by using the properties of Hermite polynomials and Gaussian integrals. This new method was applied to study the photoelectron spectra of H2O+(B~ 2B2) and D2O+(B~ 2B2), whose equilibrium geometries and harmonic vibrational frequencies were calculated by using the coupled cluster singles and doubles with perturbative triples [CCSD(T)] method together with the basis sets of 6-311++G(3df,2pd) and aug-cc-pVTZ. The adiabatic ionization energies were computed by using the CCSD(T) method extrapolated to the complete basis set limit with aug-cc-pVXZ (X=D,T,Q,5). It was found that the simulated photoelectron spectra were mainly composed of ?2 progressions and the combination bands of ?1 and ?2, whereas pure ?1 transitions should be too weak to be observable, contrary to the literature reports. It was also found that the first discernible peak in the experimental photoelectron spectra did not correspond to the adiabatic transition. The adiabatic ionization energies of H2O+(B~ 2B2) and D2O+(B~ 2B2) are proposed to be 16.78 and 16.83 eV, about 0.40 and 0.58 eV lower than the best experimental values, respectively. Conversely, the calculated ionization energies are in agreement with the proposed values within 0.02 eV.

Chang, Jia-Lin

2008-05-01

82

Brueckner-Hartree-Fock Calculations of Spherical Nuclei in an Harmonic-Oscillator Basis  

Microsoft Academic Search

A method is developed for performing Brueckner-Hartree-Fock (BHF) calculations of spherical nuclei in the harmonic-oscillator representation. Both the Brueckner and the HF self-consistencies are satisfied. The method is applied to the calculation of 16O, 40Ca, 48Ca, and 208Pb with a G matrix derived from the Hamada-Johnston potential. The nuclei are too small and underbound. Various kinds of convergence are studied.

K. T. Davies; M. Baranger; R. M. Tarbutton; T. T. Kuo

1969-01-01

83

Numerical calculation of image motion and vibration modulation transfer function  

NASA Astrophysics Data System (ADS)

In many high-resolution photographic and photoelectronic imaging systems, resolution is limited by image motion and vibration and, as a result, the high-resolution capability of the sensor may be wasted. In normal reconnaissance and robotics the sensor moves during the exposure. Some of the resulting image motion can be removed by mechanical compensation, but not all of it. The residual motion blurs the image, and usually this blur becomes the limiting factor for many high-quality imaging systems. The ever-increasing altitudes and coverage requirements of modern imaging have put a premium on high resolution. An application of this paper is the recovery of the original image by inverse filtering that depends on the modulation transfer function (MTF) of the real-time relative motion between the object and the imaging system. An original method developed here for numerically calculating MTF for any type of image motion is the basis of the paper.

Hadar, Ofer; Fisher, Moshe; Kopeika, Norman S.

1991-08-01

84

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

85

First principles calculations of the vibrational properties of icosahedral solid boron oxygen B 12O 2  

Microsoft Academic Search

In this paper, the geometrical structure and vibrational properties of icosahedral solid boron oxygen B12O2 have been calculated using first principles calculations. The symmetry of crystal vibration modes at the center of Brillouin zone is analyzed based on our numeric results and structure symmetry. The calculated results are compared with available experimental investigations.

Bin Wang; Zhaochuan Fan; Qi Zhou; Xiaoxuan Xu; Min Feng; Xuewei Cao; Yufang Wang

2011-01-01

86

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

PubMed

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

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

2012-11-01

87

Vibrational mode analysis and heat capacity calculation of K2SiSi3O9-wadeite  

NASA Astrophysics Data System (ADS)

The phonon dispersions and vibrational density of state (VDoS) of the K2SiSi3O9-wadeite (Wd) have been calculated by the first-principles method using density functional perturbation theory. The vibrational frequencies at the Brillouin zone center are in good correspondence with the Raman and infrared experimental data. The calculated VDoS was then used in conjunction with a quasi-harmonic approximation to compute the isobaric heat capacity ( C P ) and vibrational entropy (S_{298}0), yielding C P ( T) = 469.4(6) - 2.90(2) × 103 T -0.5 - 9.5(2) × 106 T -2 + 1.36(3) × 109 T -3 for the T range of 298-1,000 K and S_{298}0 = 250.4 J mol-1 K-1. In comparison, these thermodynamic properties were calculated by a second method, the classic Kieffer's lattice vibrational model. On the basis of the vibrational mode analysis facilitated by the first-principles simulation result, we developed a new Kieffer's model for the Wd phase. This new Kieffer's model yielded C P ( T) = 475.9(6) - 3.15(2) × 103 T -0.5 - 8.8(2) × 106 T -2 + 1.31(3) × 109 T -3 for the T range of 298-1,000 K and S_{298}0 = 249.5(40) J mol-1 K-1, which are in good agreement both with the results from our first method containing the component of the first-principles calculation and with some calorimetric measurements in the literature.

Chang, Linlin; Liu, Xi; Liu, Hong; Kojitani, Hiroshi; Wang, Sicheng

2013-07-01

88

Variational Calculations of IR Ro-Vibrational Spectra for Nitric Acid  

NASA Astrophysics Data System (ADS)

To model the atmospheric composition of the potentially habitable planets, it is essential to have comprehensive data on the spectroscopic properties of the main molecular absorbers. This is especially true in the infrared region which is dominated by transitions of polyatomic molecules [1]. Nitric acid (HNO3) is an important constituent of the Earth atmosphere where it is a prominent bio-signature. Here we present simulations of the absorption spectra for HNO3. We have developed a variational method to solve the ro-vibrational Schrödinger equation for a general polyatomic molecule. The ro-vibrational Hamiltonian is given by [2] where the internal curvilinear vibrational coordinates qi are used to represent the displacements of the bond lengths and bond angles, ?ij(q) are elements of the matrix of the kinematic coefficients, t is the determinant of this matrix, 'a are the Euler angles, and ?ab(q) is the inverse matrix of the tensor of inertia. The potential energy function, V (q), is given by a fourthorder polynomial expansion in terms of Morse variables xi = 1 - e-iqi for the stretching coordinates and xi = qi for the bending coordinates. The dipole moment of the molecule is presented in the form of a Taylor series of the 2nd order in terms of qi. The parameters of the potential energy and the dipole moment functions of HNO3 were calculated by the quantum chemical method at the CCSD(T)/aug-cc-pVQZ level of theory. With this potential energy function, agreement between the calculated and experimental fundamental frequencies of vibrations is within 5 cm -1. The harmonic part of the potential function was then optimized by fitting to the experimental fundamental frequencies and used to simulate the IR spectra of HNO3. The results are in good agreement with the experimental data. The figure shows an example of the simulated spectra of HNO3 in the area of the strong Fermi resonance between the -5 and 2-9 bands along with an experimental counterpart. The resulting line list can be used for modelling atmospheres of (exo)planets at elevated temperatures.

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

2013-09-01

89

Molecular structure, harmonic and anharmonic frequency calculations of 2,4-dichloropyrimidine and 4,6-dichloropyrimidine by HF and density functional methods.  

PubMed

Quantum chemical calculations of energies, geometrical structural parameters, harmonic and anharmonic frequencies of 2,4-DCP and 4,6-DCP were carried out by HF and density functional theory methods with 6-311++G(d,p) as basis set. The assignment of each normal mode has been made using the observed and calculated frequencies, their IR and Raman intensities. A detailed interpretation of the FT-IR and FT-Raman spectra of 2,4-DCP and 4,6-DCP was reported on the basis of the calculated potential energy distribution (PED). A comparison of theoretically calculated vibrational frequencies at B3LYP/6-311++G(d,p) with FT-IR and FT-Raman experimental data shows good agreement between them. Natural atomic charges of 2,4-DCP and 4,6-DCP were calculated and compared with pyrimidine molecule. PMID:21334254

Rani, Usha; Oturak, Halil; Sudha, S; Sundaraganesan, N

2011-05-01

90

Molecular structure, harmonic and anharmonic frequency calculations of 2,4-dichloropyrimidine and 4,6-dichloropyrimidine by HF and density functional methods  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations of energies, geometrical structural parameters, harmonic and anharmonic frequencies of 2,4-DCP and 4,6-DCP were carried out by HF and density functional theory methods with 6-311++G(d,p) as basis set. The assignment of each normal mode has been made using the observed and calculated frequencies, their IR and Raman intensities. A detailed interpretation of the FT-IR and FT-Raman spectra of 2,4-DCP and 4,6-DCP was reported on the basis of the calculated potential energy distribution (PED). A comparison of theoretically calculated vibrational frequencies at B3LYP/6-311++G(d,p) with FT-IR and FT-Raman experimental data shows good agreement between them. Natural atomic charges of 2,4-DCP and 4,6-DCP were calculated and compared with pyrimidine molecule.

Rani, Usha; Oturak, Halil; Sudha, S.; Sundaraganesan, N.

2011-05-01

91

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

92

Ab initio calculations with non-symmetrized hyperspherical harmonics for realistic NN potential models  

NASA Astrophysics Data System (ADS)

This contribution deals with the problem of implementing the Pauli principle in a variational calculation of the binding energy of a fermionic system on the hyperspherical harmonics (HH) basis. We summarize the main points of a method that avoids the antysimmetrization of the basis functions. In fact this gets increasingly cumbersome as the number of particles increases. The method is tested on the binding energies of two nuclei (4He and 6Li), using various nuclear potential models, including a realistic one.

Deflorian, Sergio; Barnea, Nir; Leidemann, Winfried; Orlandini, Giuseppina

2014-03-01

93

Calculation of vibration mode and its experimental study in solid rocket motors  

NASA Astrophysics Data System (ADS)

A method for the calculation of vibration mode in rocket motors is presented, and a corresponding program is worked out. Values calculated with this program are consistent with theoretical and experimental results, indicating that the program is soundly based. A new type of vibration excitation apparatus-turbo vibration exciter is also introduced and used for determination of natural frequency of acoustic cavities and of acoustic damping coefficients of motor.

Zou, Junwei; Sun, Weishen; Xing, Chunjing

1992-05-01

94

Vibration characteristics on a wind turbine rotor using modal and harmonic analysis of FEM  

Microsoft Academic Search

A wind turbine rotor system containing blades has its own characteristics. The vibration characteristics of blades with special airfoil can influence the vibration characteristics of the rotor system. This paper analyzed the vibration characteristics of a wind turbine rotor including blades with two-dimensional airfoil. The Finite Element Method (FEM) is applied to establish the rotor model, with the purpose that

Chao Liu; Dongxiang Jiang; Jie Chen

2010-01-01

95

Tunable harmonic vibrations of quasi one-dimensional conductors induced by sliding charge-density waves  

NASA Astrophysics Data System (ADS)

We demonstrate that samples of quasi one-dimensional compounds show torsional vibrations induced by the sliding charge-density wave (CDW). Narrowband noise at the fundamental frequency is found in the vibrations spectra. The result suggests an approach to studies of the CDW dynamics and presents CDW conductors as tunable (ultra)sonic acoustoelectronic generators—unique solids vibrating under dc voltage.

Nikitin, M. V.; Zybtsev, S. G.; Pokrovskii, V. Ya.

2012-07-01

96

Lattice Monte Carlo calculations for unitary fermions in a harmonic trap  

SciTech Connect

We present a lattice Monte Carlo approach developed for studying large numbers of strongly interacting nonrelativistic fermions and apply it to a dilute gas of unitary fermions confined to a harmonic trap. In place of importance sampling, our approach makes use of high statistics, an improved action, and recently proposed statistical techniques. We show how improvement of the lattice action can remove discretization and finite volume errors systematically. For N=3 unitary fermions in a box, our errors in the energy scale as the inverse lattice volume, and we reproduce a previous high-precision benchmark calculation to within our 0.3% uncertainty; as additional benchmarks we reproduce precision calculations of N=3,...,6 unitary fermions in a harmonic trap to within our {approx}1% uncertainty. We then use this action to determine the ground-state energies of up to 70 unpolarized fermions trapped in a harmonic potential on a lattice as large as 64{sup 3}x72. In contrast to variational calculations, we find evidence for persistent deviations from the thermodynamic limit for the range of N considered.

Endres, Michael G.; Kaplan, David B.; Lee, Jong-Wan; Nicholson, Amy N. [Physics Department, Columbia University, New York, New York 10027 (United States); Theoretical Research Division, RIKEN Nishina Center, Wako, Saitama 351-0198 (Japan); Institute for Nuclear Theory, University of Washington, Seattle, Washington 98195-1550 (United States)

2011-10-15

97

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

98

Structural, electronic, elastic, thermodynamic and vibration properties of TbN compound from first principles calculations  

NASA Astrophysics Data System (ADS)

We have predicted structural, electronic, elastic, thermodynamic and vibration characteristics of TbN, using density functional theory within generalized-gradient (GGA) apraximation. For the total energy calculation we have used the projected augmented plane-wave (PAW) implementation of the Vienna Ab initio Simulation Package (VASP). We have used to examine structure parameter in eight different structures such as in NaCl (B1), CsCl (B2), ZB (B3), Tetragonal (L10), WC (Bh), NiAs (B8), PbO (B10) and Wurtzite (B4). We have performed the thermodynamics properties for TbN by using quasi-harmonic Debye model. We have, also, predicted the temperature and pressure variation of the volume, bulk modulus, thermal expansion coefficient, heat capacities and Debye temperatures in a wide pressure (0-130 GPa) and temperature ranges (0-2000 K). Furthermore, the band structure, phonon dispersion curves and corresponding density of states are computed. Our results are compared to other theoretical and experimental works, and excellent agreement is obtained.

Ciftci, Y. O.; Ozayman, M.; Surucu, G.; Colakoglu, K.; Deligoz, E.

2012-03-01

99

On methods for application of harmonic control. [helicopter vibration reduction by blade pitch variation  

NASA Technical Reports Server (NTRS)

The paper presents data which confirm the effectiveness of higher harmonic blade pitch control in substantially reducing helicopter rotor vibratory hub loads. The data are the result of recent tests on a 2.7-m model conducted in the Langley Research Center's transonic dynamics wind tunnel. Several predictive analyses developed in support of the NASA program are shown capable of accurately predicting both amplitude and phase of the higher harmonic control input required to nullify a single 4/rev force or moment input. The use of multiple blade feathering inputs in the design of a flightworthy higher harmonic control system is discussed.

Wood, E. R.; Powers, R. W.; Hammond, C. E.

1978-01-01

100

Structural, Conformational and Vibrational Studies of Isocyanocyclopentane from Infrared, Raman Spectra and AB Initio Calculations  

NASA Astrophysics Data System (ADS)

The infrared and Raman spectra (3200 to 50 cm^{-1}) of the gas, liquid or solution, and solid have been recorded of isocyanocyclopentane, _{c}-C_{5}H_{9}NC. FT-microwave studies have also been carried out and 23 transitions were recorded for the envelope-axial (Ax) conformer. Variable temperature (-55 to -100°C) studies of the infrared spectra (3200 to 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 ± 0.03 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 heavy atom distances (Å): C?N = 1.176 ; C_{?}-N?C= 1.432; C_{?}-C_{?},C_{?}' = 1.534; C_{?}-C_{?}, C_{?}' = 1.542; C_{?}-C_{?}' = 1.554 and angles (°:angleC_{?}-N?C = 177.8; angleC_{?}C_{?}-N?C = 110.4; angleC_{?}C_{?}C_{?}'= 102.9; angleC_{?}C_{?}C_{?} = 103.6; angleC_{?}C_{?}C_{?}' = 105.9. The results are discussed and compared to the corresponding properties of some related molecules.

Sawant, Dattatray K.; Klaassen, Joshua J.; Durig, James R.

2013-06-01

101

Calculation of Out?of?Plane Vibrations of a Porphin Molecule  

Microsoft Academic Search

Using the DFT\\/B3LYP method with the base set 6-31G**, we carried out calculation of the frequencies of the normal vibrations of porphin and of its five isotopic types. Scaling of force constants for out-of-plane vibrations has been performed in independent natural coordinates. The symmetry coordinates are introduced and a force field for out-of plane vibrations of a porphin molecule in

K. V. Berezin; O. D. Tatarenko; V. V. Nechaev

2002-01-01

102

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

NASA Astrophysics Data System (ADS)

We present Floquet calculations of high harmonic generation (HHG) for the lowest two electronic states of the {H}_2^+ ion by strong continuous-wave laser fields. We solve the non-Hermitian matrix problem to get accurate solutions to the periodic time-dependent Schrödinger equation (TDSE) by applying a pseudospectral representation combined with a complex absorbing potential method. This represents an alternative approach to direct TDSE solutions to obtain the harmonic spectra for the ion. We compare our HHG rates for the lower and upper states of {H}^{+}_{2}, which correspond to the gerade and ungerade ground states in the field-free case, with previously obtained results in the literature. We show that the enhancement of the ionization rates at the critical internuclear separation Rc ? 8?au plays some role in the appearance of very strong harmonic orders n = 5–11 at ? = 1064?nm and n = 5–9 at ? = 800?nm and intensity I = 1014?W?cm?2.

Tsogbayar, Ts; Horbatsch, M.

2014-06-01

103

Vibrational Assignments and Electronic Structure Calculations for 3-Chloro-4-Hydroxybenzaldehyde  

Microsoft Academic Search

Fourier-Transform Laser Raman (3500-50 cm-1) and Infrared (4000-400 cm-1) spectral measurements have been made for the solid 3-Chloro-4-hydroxybenzaldehyde. Electronic ground state energy, equilibrium structure, harmonic vibrational frequencies, depolarization ratios, force constants and normal modes have been computed at two levels of theory, namely, Restricted Hartree-Fock (RHF) and Becke's three parameter-hybrid functional combined with Lee-Yang-Parr correlation (B3LYP) combined with 6-31G* basis

Nandini V. Arlikatti; Anita R. Shettar; J. Tonannavar; Jayashree Yenagi

2008-01-01

104

Limits on high-order harmonic generation from single-atom calculations  

SciTech Connect

In the quantum mechanical calculations of electron and photon emission from atoms in strong laser fields we have employed a single-active-electron (SAE) model. We determine the effect of the time varying electric field of the laser on each of the valence electrons separately. The active electron in each calculation moves in the time-independent mean field of the remaining, unexcited electrons and the nucleus. This approach works well for the rare gas atoms, at least partially because the neglected double or higher excitations involve states well above the ionization threshold. The photoelectron and photon emission spectra calculated using this technique agree quantitatively with observed emission rates. In this paper we will present a simple semiclassical model for high intensity ionization which reproduces the observed harmonic emission spectra obtained in this regime and which provides considerable insight into the dynamics of this process. The basic models has been used in the past to predict electron energy distributions in the tunneling regime and we will use it here for harmonics.

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

1993-08-18

105

Structural conformations, tautomerization and vibrational spectral study of 6-amino-1-methylpurine with density functional theoretical calculations  

NASA Astrophysics Data System (ADS)

The FT-IR and FT-Raman spectra of 6-amino-1-methylpurine (AMP) have been recorded in the region 4000-400 cm-1 and 3500-50 cm-1 respectively. The optimized geometry, frequency and intensity of the vibrational bands of AMP have been obtained by DFT level of theory using B3LYP method with 6-311++G(d,p) basis set. A complete vibrational assignment aided by the theoretical harmonic frequency analysis has been proposed. Purines, including substituted purines and their tautomers, are the most widely occurring nitrogen-containing heterocyclic in nature. Purines and pyrimidines make up the two groups of nitrogenous bases, including the two groups of nucleotide bases. Two of the four deoxyribonucleotides and two of the four ribonucleotides, the respective building-blocks of DNA and RNA, are purines. The calculated vibrational values are in good agreement when they are compared with IR and Raman experimental data. Amine-imine tautomerism of 6-amino-1-methyl purine is studied in detail. In agreement with experimental results, it was found that imine tautomer is more stable than amine tautomer.

Arivazhagan, M.; Kavitha, R.; Subhasini, V. P.

2014-07-01

106

Calculation of ground vibration spectra from heavy military vehicles  

Microsoft Academic Search

The demand for reliable autonomous systems capable to detect and identify heavy military vehicles becomes an important issue for UN peacekeeping forces in the current delicate political climate. A promising method of detection and identification is the one using the information extracted from ground vibration spectra generated by heavy military vehicles, often termed as their seismic signatures. This paper presents

V. V. Krylov; S. Pickup; J. McNuff

2010-01-01

107

Using Generalized Vibrational Methods in the Calculation of Plates.  

National Technical Information Service (NTIS)

Vibrational methods are used in place of the differential equations to solve problems dealing with the theory of elasticity. Some works connected with this problem are discussed and the variation of a functional developed by I. G. Teregulov is used in thi...

A. I. Kutikov I. G. Teregulov Y. I. Butenko

1973-01-01

108

Threshold photoionization spectra of benzyl radical: Cation vibrational states and {ital ab} {ital initio} calculations  

SciTech Connect

We measured threshold photoionization spectra of benzyl{sup +}-{ital h}{sub 7}, benzyl{sup +}-{alpha}{ital d}{sub 2}, and benzyl{sup +}-{ital d}{sub 7} in the ground electronic state ({tilde {ital X}}{sup +1}{ital A}{sub 1}) using resonant two-photon excitation and detection of electrons by pulsed field ionization. The adiabatic ionization potentials of benzyl-{ital h}{sub 7}, benzyl-{alpha}{ital d}{sub 2}, and benzyl-{ital d}{sub 7} are 58468{+-}5 cm{sup -1}, 58418{+-}5 cm{sup -1}, and 58386{+-}5 cm{sup -1}. Excitation through a variety of vibronically mixed {tilde {ital A}}{sup 2}{ital A}{sub 2}-{tilde {ital B}}{sup 2}{ital B}{sub 2} neutral excited states allows observation of cation vibrations of both {ital a}{sub 1} and {ital b}{sub 1} symmetries. We directly measure in-plane fundamentals and infer the frequencies of certain out-of-plane fundamentals from their involvement in combinations or overtones. By comparison with harmonic frequencies from {ital ab initio} calculations, we assign 35 of 48 observed levels in the -{ital h}{sub 7} isotopomer, 15 of 22 levels in -{alpha}{ital d}{sub 2}, and 25 of 30 levels in -{ital d}{sub 7}. {ital ab initio} calculations permit a detailed comparison of the geometry, chemical bonding, and vibrational frequencies in the benzyl anion, neutral, and cation. The anion and cation, both closed-shell species, have similar geometries with relatively short exocyclic CC bond (1.371 A and 1.372 A, respectively) and with the aromatic ring compressed along the {ital C}{sub 2} symmetry axis. The neutral free radical has a longer exocyclic CC bond (1.413 A) and a more nearly sixfold symmetric ring. The natural resonance theory provides bond orders and resonance-structure weights in all three species. While no single resonance structure dominates in any of the three species, the structure with an exocyclic CC double bond is more important in the anion and cation than in the neutral. {copyright} {ital 1996 American Institute of Physics.}

Eiden, G.C.; Lu, K.; Badenhoop, J.; Weinhold, F.; Weisshaar, J.C. [Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)] [Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

1996-06-01

109

Vibrational spectra and harmonic force fields of pyrrolidine derivatives: comparison between HF, MP2 and DFT force fields  

Microsoft Academic Search

Infrared and Raman spectra are reported for the isotopic species of pyrrolidine-d0 (PY) and -d1 and for N-methylpyrrolidine-d0 (NMP), -d2, -d3 and -d8. A complete assignment of the experimentally observed bands to normal modes is presented and discussed in particular in the CH\\/CD stretching region. The molecular structures and harmonic force fields were calculated ab initio at the Hartree–Fock (HF),

Ferenc Billes; Ekkehard Geidel

1997-01-01

110

Non-linear vibration of coupled duffing oscillators by an improved incremental harmonic balance method  

Microsoft Academic Search

The incremental harmonic balance method is improved by (i) reversing the order of increment and linearization to find the bifurcated solution branches, (ii) using a fast Fourier transform to compute the solution increments and the Floquet matrix, and (iii) finding the secondary path after a bifurcation by an improved arc-length method. A system of two Duffing oscillators linked with a

A. Y. T. Leung; S. K. Chui

1995-01-01

111

An effective scaling frequency factor method for harmonic vibrational frequencies: The factors’ transferability problem  

Microsoft Academic Search

Performance of the so-called effective scaling frequency factor method, ESFF, for scaling of harmonic theoretical frequencies is analyzed and compared with the well-known SQM method. A training set of 30 molecules (660 experimental frequencies) has been used to optimize a set of 11 scaling factors. Results point towards somewhat lower RMS deviation with respect to the experimental values obtained with

Piotr Borowski; Aleksandra Drzewiecka; Manuel Fernández-Gómez; Maria Paz Fernández-Liencres; Tomás Peña Ruiz

2008-01-01

112

Vibrationally and rotationally nonadiabatic calculations on H3+ using coordinate-dependent vibrational and rotational masses  

NASA Astrophysics Data System (ADS)

Using the core-mass approach, we have generated a vibrational-mass surface for the triatomic H3+. The coordinate-dependent masses account for the off-resonance nonadiabatic coupling and permit a very accurate determination of the rovibrational states using a single potential energy surface. The new, high-precision measurements of 12 rovibrational transitions in the ?2 bending fundamental of H3+ by Wu [Phys. Rev. A1050-294710.1103/PhysRevA.88.032507 88, 032507 (2013)] are used to scale this surface empirically and to derive state-dependent vibrational and rotational masses that reproduce the experimental transition energies to 10-3cm-1. Rotational term values for J?10 are presented for the two lowest vibrational states and equivalent transitions in D3+ considered.

Diniz, Leonardo G.; Mohallem, José Rachid; Alijah, Alexander; Pavanello, Michele; Adamowicz, Ludwik; Polyansky, Oleg L.; Tennyson, Jonathan

2013-09-01

113

First-principles calculation of vibrational Raman spectra of tetrahedral amorphous carbon  

NASA Astrophysics Data System (ADS)

The nonresonant vibrational Raman spectra of tetrahedral amorphous carbon are calculated from first principles. The structural model was generated using Car-Parinello molecular dynamics, the vibrational modes are determined using the linear response approach and Raman tensors are calculated using the finite electric field method. Our theoretical visible and reduced Raman spectra show an overall good agreement with experimental spectra, and better than previous calculated results. The analysis in terms of atomic vibrations shows that the Raman spectrum mainly comes from sp 2 contribution, G peak is due to the stretching vibration of any pair of sp 2 atoms and only a small sp 3 contribution can be noticed. The differences between peak intensities of reduced theoretical and experimental results mainly come from defects and the high sp 3 content in our simulated structure.

Niu, Li; Zhu, Jiaqi; Gao, Wei; Liu, Aiping; Han, Xiao; Du, Shanyi

2008-10-01

114

Vibrational analysis of nicotinic acid species based on ab initio molecular orbital calculations  

NASA Astrophysics Data System (ADS)

In this work a vibrational investigation of the equilibrium species in aqueous solution of nicotinic acid was performed, by both experimental as well as theoretical methods. The Raman spectra of its aqueous solutions at some pH values were obtained and analyzed considering the equilibrium of three main species: a totally protonated one, a zwitterionic form, and the nicotinate anion. These species were also studied by ab initio (Hartree-Fock and second-order Møller-Plesset perturbation) and hybrid density functional theory calculations. The structures of these species were optimized and the vibrational frequencies calculated. These methods provided a good correlation between the calculated and the experimental vibrational frequencies. A great mixing of the ring vibrational modes, as well as between the ring and the substituent modes, was observed.

Sala, O.; Gonçalves, N. S.; Noda, L. K.

2001-05-01

115

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

116

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.

117

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

118

Vibrational properties of correlated systems from ab-initio calculations  

NASA Astrophysics Data System (ADS)

In this talk I will present a recent extension of Density Functional Perturbation Theory to the DFT+U energy functional that allows to compute the vibrational properties of materials from their correlated ground state. The new computational tool, named DFPT+U, is used to investigate the phonon spectrum of MnO and NiO. The more accurate account of electronic correlation through the Hubbard-corrected functional results in a significant improvement in the agreement between the computed phonon frequencies and available experiments. In particular, we obtain a significant reduction in the splitting between the center-zone optical modes (due to the antiferromagnetic order) that confirms the importance of electronic localization in the description of magnetic couplings between metal ions. The order of the split optical modes is also shown to correlate with the occupation of the d states of the transition metal atoms opening for the possibility to use measurements of the vibrational frequencies to investigate certain aspects of the electronic structure of these compounds. In the last part of the talk I will also present the application of DFPT+U to Cu compounds and will discuss the possibility to use it to compute the electron-phonon coupling of high Tc superconductors.

Cococcioni, Matteo; Himmetoglu, Burak; Floris, Andrea

2012-02-01

119

Matrix-isolation FT-IR studies and theoretical calculations of the vibrational properties of 4-methyl-2 '-hydroxy-4 '-ethyloxyazobenzene  

NASA Astrophysics Data System (ADS)

The vibrational spectrum of 4-methyl-2 '-hydroxy-4 '-ethyloxyazobenzene (MHEAB) has been studied in low-temperature argon matrices and in CCl 4 solutions. Calculations at the DFT (B3-LYP) level of theory with the 6-31++G** basis set, as well as additional IR experiments of deuterated samples and of derivatives without the OH group, have been used to analyze the IR MHEAB spectrum. In the calculations we used the conventional harmonic approach, as well as an approach based on an one-dimensional anharmonic model. It has been shown that introduction of the OH group into the compound and formation of the OH⋯N intra-molecular hydrogen bond cause an increase of the intensity of the stretching N?N mode, but do not affect the frequencies of the azo-bridge vibrations.

Pajak, J.; Ramaekers, R.; Rospenk, M.; Alexandrov, V.; Stepanian, S.; Adamowicz, L.; Maes, G.

2003-01-01

120

Vibrational properties and Raman spectra of different edge graphene nanoribbons, studied by first-principles calculations  

NASA Astrophysics Data System (ADS)

The vibrational properties and Raman spectra of graphene nanoribbons with six different edges have been studied by using the first-principles calculations. It is found that edge reconstruction leads to the emergence of localized vibrational modes and new topological defect modes, making the different edges identified by polarized Raman spectra. The radial breathing-like modes are found to be independent of the edge structures, while the G-band-related modes are affected by different edge structures. Our results suggest that the polarized Raman spectrum could be a powerful experimental tool for distinguishing the GNRs with different edge structures due to their different vibrational properties.

Hu, Ting; Zhou, Jian; Dong, Jinming

2013-01-01

121

Vibrational energies of PH3 calculated variationally at the complete basis set limit.  

PubMed

The potential energy surface for the electronic ground state of PH(3) was calculated at the CCSD(T) level using aug-cc-pV(Q+d)Z and aug-cc-pVQZ basis sets for P and H, respectively, with scalar relativistic corrections included. A parametrized function was fitted through these ab initio points, and one parameter of this function was empirically adjusted. This analytical PES was employed in variational calculations of vibrational energies with the newly developed program TROVE. The convergence of the calculated vibrational energies with increasing vibrational basis set size was improved by means of an extrapolation scheme analogous to the complete basis set limit schemes used in ab initio electronic structure calculations. The resulting theoretical energy values are in excellent agreement with the available experimentally derived values. PMID:18681648

Ovsyannikov, Roman I; Thiel, Walter; Yurchenko, Sergei N; Carvajal, Miguel; Jensen, Per

2008-07-28

122

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

123

The assignment of the vibrations of substituted mercaptotetrazoles based on quantum chemical calculations  

NASA Astrophysics Data System (ADS)

We studied four substituted mercaptotetrazoles using IR- and Raman-spectroscopy on the bulk substance and surface enhanced Raman spectroscopy (SERS) on a silver colloid. Semiempirical and ab initio calculations with various basis sets were performed to establish an assignment of the experimentally observed bands to the calculated ones. We found a satisfactory agreement between the calculated and observed frequencies of CH/CC-vibrations in the phenyl ring and encountered problems with the tetrazole ring vibrations. The PM3 hamiltonian failed for the SH group.

Sägmüller, Bernd; Freunscht, Peter; Schneider, Siegfried

1999-05-01

124

Image resolution limits resulting from mechanical vibrations. III - Numerical calculation of modulation transfer function  

Microsoft Academic Search

A method of numerical calculation of MTF, relevant in principle to any type of image motion, is presented. It is demonstrated here for linear, high, and low vibration frequencies. The method yields the expected closed form solutions for linear and high-frequency motion. The low-vibration-frequency situation involves random process blur radii and MTFs that can only be handled statistically since no

Ofer Hadar; Moshe Fisher; N. S. Kopeika

1992-01-01

125

Calculation of vibrational spectra of an icosahedral quasicrystal AlCuFe  

SciTech Connect

Vibrational spectra of an icosahedral quasicrystal AlCuFe have been calculated on the basis of a crystalline 1/1 approximant by the recurrence method. To describe the interaction of atoms in a quasicrystal, the semiempirical EAM model was used. It is shown that the calculated spectra are in satisfactory agreement with the experimental neutron inelastic scattering data.

Rudenko, A. N., E-mail: ran@infoteck.ru; Mazurenko, V. G. [Ural State University (Russian Federation)

2007-11-15

126

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

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

127

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

PubMed

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

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

2011-01-01

128

Modelling of Rail Vehicles and Track for Calculation of Ground-Vibration Transmission Into Buildings  

NASA Astrophysics Data System (ADS)

A methodology for the calculation of vibration transmission from railways into buildings is presented. The method permits existing models of railway vehicles and track to be incorporated and it has application to any model of vibration transmission through the ground. Special attention is paid to the relative phasing between adjacent axle-force inputs to the rail, so that vibration transmission may be calculated as a random process. The vehicle-track model is used in conjunction with a building model of infinite length. The tracking and building are infinite and parallel to each other and forces applied are statistically stationary in space so that vibration levels at any two points along the building are the same. The methodology is two-dimensional for the purpose of application of random process theory, but fully three-dimensional for calculation of vibration transmission from the track and through the ground into the foundations of the building. The computational efficiency of the method will interest engineers faced with the task of reducing vibration levels in buildings. It is possible to assess the relative merits of using rail pads, under-sleeper pads, ballast mats, floating-slab track or base isolation for particular applications.

Hunt, H. E. M.

1996-05-01

129

Vibrational spectra, ab initio/DFT electronic structure calculations, and normal coordinate analysis of 2-bromo-5-fluorobenzaldehyde.  

PubMed

FT-IR (4000-400 cm(-1)) and FT-Raman (3500-50 cm(-1)) spectral measurements of solid samples of 2-bromo-5-fluorobenzaldehyde (BFB) have been done. Ab initio (RHF/6-311G*) and DFT (B3LY/6-311G* and B3PW91/6-311G*) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, infrared intensities, Raman activities and atomic displacements. Furthermore force field calculations have been performed by normal coordinate analysis. Force field calculations showed that several normal modes are mixed in terms of the internal coordinates. A complete assignment of the observed spectra, based on spectral correlations, electronic structure and normal coordinate analysis, has been proposed. Optimization leads to C(S) symmetry with O-trans and O-cis isomers, with respect to aldehydic oxygen and bromine, with O-trans-isomer as the low energy stable form. The energy difference between the two isomers is 2.95084 kcal/mol. The results of the calculations have been used to simulate IR and Raman spectra for BFB that showed excellent agreement with the observed spectra. The SQM method, which implies multiple scaling of the ab initio and DFT force fields has been shown superior to the uniform scaling approach. PMID:19864179

Hiremath, C S; Sundius, Tom

2009-12-01

130

Vibrational spectra, ab initio/DFT electronic structure calculations, and normal coordinate analysis of 2-bromo-5-fluorobenzaldehyde  

NASA Astrophysics Data System (ADS)

FT-IR (4000-400 cm -1) and FT-Raman (3500-50 cm -1) spectral measurements of solid samples of 2-bromo-5-fluorobenzaldehyde (BFB) have been done. Ab initio (RHF/6-311G*) and DFT (B3LY/6-311G* and B3PW91/6-311G*) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, infrared intensities, Raman activities and atomic displacements. Furthermore force field calculations have been performed by normal coordinate analysis. Force field calculations showed that several normal modes are mixed in terms of the internal coordinates. A complete assignment of the observed spectra, based on spectral correlations, electronic structure and normal coordinate analysis, has been proposed. Optimization leads to C S symmetry with O- trans and O- cis isomers, with respect to aldehydic oxygen and bromine, with O- trans-isomer as the low energy stable form. The energy difference between the two isomers is 2.95084 kcal/mol. The results of the calculations have been used to simulate IR and Raman spectra for BFB that showed excellent agreement with the observed spectra. The SQM method, which implies multiple scaling of the ab initio and DFT force fields has been shown superior to the uniform scaling approach.

Hiremath, C. S.; Sundius, Tom

2009-12-01

131

Ab initio calculation of vibrational Raman optical activity  

NASA Astrophysics Data System (ADS)

We review recent developments in the ab initio calculation of Raman optical activity (ROA) and discuss the applications of modern ab initio methods to the calculation of these properties, giving some examples of the kind of molecules and questions that can now be addressed using ab initio methodology. We also give some perspectives on future developments and applications of theoretical methods as an aid in understanding and analyzing ROA spectra.

Pecul, Magdalena; Ruud, Kenneth

132

Vibrational spectra of 1-methylthyminate complexes with mercury(II) and potassium and ab initio calculations of the 1MeT anion  

Microsoft Academic Search

The FT-Raman and FT-infrared spectra of bis(1-methylthyminato)mercury(II), Hg(1-MeT)2, and potassium 1-methylthyminate, K(1-MeT), are reported. The molecular structure, harmonic vibrational frequencies, infrared intensities and Raman scattering activities of the N3-deprotonated 1-MeT anion have been calculated at the HF\\/6-31++G?? and MP2\\/D95V?? levels of theory. A rigorous normal coordinate analysis of the 1-MeT anion has been made. The ab initio predicted frequencies and

Barbara Morzyk-Ociepa; Danuta Michalska

2001-01-01

133

A simplified spherical harmonic method for coupled electron-photon transport calculations  

SciTech Connect

In this thesis the author has developed a simplified spherical harmonic method (SP{sub N} method) and associated efficient solution techniques for 2-D multigroup electron-photon transport calculations. The SP{sub N} method has never before been applied to charged-particle transport. He has performed a first time Fourier analysis of the source iteration scheme and the P{sub 1} diffusion synthetic acceleration (DSA) scheme applied to the 2-D SP{sub N} equations. The theoretical analyses indicate that the source iteration and P{sub 1} DSA schemes are as effective for the 2-D SP{sub N} equations as for the 1-D S{sub N} equations. In addition, he has applied an angular multigrid acceleration scheme, and computationally demonstrated that it performs as well as for the 2-D SP{sub N} equations as for the 1-D S{sub N} equations. It has previously been shown for 1-D S{sub N} calculations that this scheme is much more effective than the DSA scheme when scattering is highly forward-peaked. The author has investigated the applicability of the SP{sub N} approximation to two different physical classes of problems: satellite electronics shielding from geomagnetically trapped electrons, and electron beam problems.

Josef, J.A.

1997-12-01

134

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

135

Temperature dependence of the optical rotation in six bicyclic organic molecules calculated by vibrational averaging.  

PubMed

The vibrational corrections and the temperature dependence of the specific rotation of six rigid organic molecules (alpha-pinene, beta-pinene, cis-pinane, camphene, camphor, and fenchone) were calculated at three wavelengths using hybrid time-dependent density functional theory (TDDFT). A technique for calculating the temperature dependence of the vibrational average of a molecular property has been applied to obtain the specific rotation of the molecules as a function of temperature. For cases in which accurate equilibrium optical rotations can be obtained as a "base value," and for which there is little effect from solvation, accurate predictions of the trends in the temperature-dependence of the specific rotations can be calculated. For other cases, the method can be used to extract purely vibrational contributions to the overall temperature dependence of optical rotation. PMID:17304606

Mort, Brendan C; Autschbach, Jochen

2007-03-12

136

Ab initio calculation of atomic axial tensors and vibrational rotational strengths using density functional theory  

Microsoft Academic Search

The first application of the density functional theory (DFT) to the calculation of atomic axial tensors (AATs) is reported. Analytical derivative methods and gauge-invariant atomic orbitals (GIAOs) are employed. DFT\\/GIAO AATs for trans-2,3 d2-oxirane calculated using a [8s6p3d\\/6s3p] basis set and the Becke 3-Lee-Yang-Parr hybrid density functional, in combination with a DFT harmonic force field and atomic polar tensors (APTs),

J. R. Cheeseman; M. J. Frisch; F. J. Devlin; P. J. Stephens

1996-01-01

137

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

PubMed

A transformation of potential energy surfaces (PES) being represented by multi-mode expansions is introduced, which allows for the calculation of anharmonic vibrational spectra of any isotopologue from a single PES. This simplifies the analysis of infrared spectra due to significant CPU-time savings. An investigation of remaining deviations due to truncations and the so-called multi-level approximation is provided. The importance of vibrational-rotational couplings for small molecules is discussed in detail. In addition, an analysis is proposed, which provides information about the quality of the transformation prior to its execution. Benchmark calculations are provided for a set of small molecules. PMID:24832257

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

2014-05-14

138

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

NASA Astrophysics Data System (ADS)

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; Berger, Robert; Rauhut, Guntram

2014-05-01

139

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

140

Application of asymptotic methods of nonlinear vibration theory to the calculation of grouping in a drift-tube klystron  

Microsoft Academic Search

Electron grouping in a drift-tube klystron is analyzed, making allowance for changes in electron-flux natural vibration frequency in time. An analytical solution to a nonlinear vibration equation is used to plot the optimal length of the drift tube against the initial rate of modulation. Empirical formulas for calculating the mean natural vibration frequency in a klystron drift tube are proposed.

Iu. A. Katsman; S. M. Movnin; V. D. Trebich

1977-01-01

141

Vibrational spectra, theoretical calculations, and structure of 4-silaspiro(3,3)heptane  

NASA Astrophysics Data System (ADS)

Theoretical computations have been carried out for 4-silaspiro(3,3)heptane (SSH) in order to calculate its structure and vibrational spectra. SSH was found to have two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. The puckering and tilting reduce the D2d symmetry to C2. Nonetheless, the vibrational assignments can be done quite well on the basis of D2d symmetry. This is confirmed by the fact that all but the lowest E vibrations show insignificant splitting into A and B modes of C2 symmetry. However, the observed splittings of the lowest frequency modes do confirm the lower conformational symmetry. The calculated infrared and Raman spectra were compared to the experimental spectra collected for the vapor, liquid, and solid states, and the agreement is excellent.

Ocola, Esther J.; Medders, Cross; Cooke, Joel M.; Laane, Jaan

2014-09-01

142

Vibrational spectra, theoretical calculations, and structure of 4-silaspiro(3,3)heptane.  

PubMed

Theoretical computations have been carried out for 4-silaspiro(3,3)heptane (SSH) in order to calculate its structure and vibrational spectra. SSH was found to have two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. The puckering and tilting reduce the D2d symmetry to C2. Nonetheless, the vibrational assignments can be done quite well on the basis of D2d symmetry. This is confirmed by the fact that all but the lowest E vibrations show insignificant splitting into A and B modes of C2 symmetry. However, the observed splittings of the lowest frequency modes do confirm the lower conformational symmetry. The calculated infrared and Raman spectra were compared to the experimental spectra collected for the vapor, liquid, and solid states, and the agreement is excellent. PMID:24810025

Ocola, Esther J; Medders, Cross; Cooke, Joel M; Laane, Jaan

2014-09-15

143

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

144

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

145

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

146

Theoretical calculation and vibrational spectral analysis of L-arginine trifluoroacetate  

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

147

Vibrational properties of alkyl monolayers on Si(111) surfaces: Predictions from ab-initio calculations  

NASA Astrophysics Data System (ADS)

Vibrational properties of Si(111) surfaces terminated by different functional groups have been investigated using density functional theory (DFT). The variations in methyl-related frequencies in different chemical environments, e.g., in methane, methylsilane and ethylsilane, and the methyl- and ethyl-terminated Si(111) surfaces are well predicted by DFT within the local density approximation. In particular, DFT calculations provide useful information on trends and mode assignments in cases where the surface coverage and morphology are not well established experimentally, e.g., in the case of the ethyl-terminated Si(111) surface. Influences of DFT exchange-correlation functionals and anharmonic effects on computed vibrational frequencies are discussed.

Li, Yan; Galli, Giulia

2012-02-01

148

The use of the hybrid density functional theory (DFT) approach for calculation of vibrational spectra: nitromethane  

Microsoft Academic Search

The molecular geometry of nitromethane was optimized and its force field and vibrational spectrum were calculated by the BECKE3LYP\\u000a method. The accuracy of optimization of the geometry of MeNO2 obtained by this method using the 6–311G(d,p) and 6–311++G(d,p) basis sets is not poorer than that obtained at the second-order\\u000a Mller-Plesset level of perturbation theory (MP2). The vibrational frequencies of nitromethane

I. V. Tokmakov; V. A. Shlyapochnikov

1997-01-01

149

Temperature dependence of the optical rotation of fenchone calculated by vibrational averaging.  

PubMed

On the basis of vibrational averaging, the temperature dependence of the optical rotation for fenchone has been calculated using TDDFT with the B3LYP hybrid functional at three wavelengths. The results show that very good agreement is obtained between theory and experiment. It is concluded that temperature-dependent vibrational effects are likely to account for much of the observed temperature dependence in optical rotation exhibited by rigid organic molecules in case there is only a weak temperature-dependent interaction with the solvent. PMID:17020244

Mort, Brendan C; Autschbach, Jochen

2006-10-12

150

Vibrations  

NASA Astrophysics Data System (ADS)

Low frequent vibrations may cause from disturbing up to damaging effects. There is no precise distinction between structure-borne sound and vibrations. However - depending on the frequency range - measurements and predictions require different techniques. In a wide frequency range, the generation, transmission and propagation of vibrations can be investigated similar to structure-borne sound (see Chap. 9).

Guggenberger, Johannes; Müller, Gerhard

151

Vibrational spectra, conformational equilibria, ab initio calculations and vibrational assignments of ethylmethylfluorosilane  

NASA Astrophysics Data System (ADS)

The infrared spectra of ethylmethylfluorosilane (CH 3SiHFCH 2CH 3) have been recorded as a vapour, liquid and solid at 78 K in the 4000-50 cm -1 range and isolated in an argon matrix at ca. 5 K. Infrared spectra of two different solid phases were obtained after annealing to temperatures of 120 and 130 K, and recooling to 78 K. Although the IR spectra were quite similar in the MIR region, certain differences were noted in the FIR region below 400 cm -1. The most stable conformer MeMe was present after annealing to 130 K, but three bands belonging to MeH were detected after annealing to 120 K. Various infrared bands changed intensity when the argon matrix was annealed to temperatures between 20 and 35 K, and some of these were related to changes in the conformational abundance. Raman spectra of the liquid were recorded at room temperature and at various temperatures between 295 and 153 K. Spectra of an amorphous and annealed solid were recorded at 78 K. In the variable temperature Raman spectra, various bands changed in intensity and were interpreted in terms of conformational equilibria between the three possible conformers. Complete assignments were made for all the bands of the most stable conformer MeMe. From various bands assigned to the three conformers, the conformational enthalpy difference ? H from MeMe to the intermediate energy conformer MeH was found to be 0.5 kJ mol -1 and to the highest conformer MeF was 0.7 kJ mol -1. At ambient temperature this leads to 39% MeMe, 32% MeH and 29% of the MeF conformer in the liquid. Ab initio calculations in the RHF, MP2, DFT approximations and very accurate G2 calculations were carried out. With one exception, the MeMe conformer had the lowest enthalpy in all these calculations, the MeH had the intermediate and the MeF the highest enthalpy, and the calculations were in good agreement with the measurements.

Guirgis, Gamil A.; Horn, Anne; Klaeboe, Peter; Nielsen, Claus J.

2006-12-01

152

Exploring C-H···O hydrogen bonds in dihydrocoumarin from combined vibrational spectroscopy and DFT calculations  

NASA Astrophysics Data System (ADS)

The complete vibrational spectra assignment of dihydrocoumarin is performed through a combined vibrational spectroscopy and DFT calculations approach. To provide effective information, vibrational analysis was also performed for ?-pyrone and coumarin related systems. The presence of extra components in the ?Cdbnd O band profile can only be understood by both Fermi resonance and monomer/dimer equilibrium phenomena, the latter established by C-H···O hydrogen bond with ?H° value of -8.4 ± 0.9 kJ mol-1. The analysis of the ?C-H region indicates that both the methylene and aromatic C-H groups have a significant contribution to the formation of C-H···O bonded dimers in liquid dihydrocoumarin.

Nolasco, Mariela M.; Vaz, Patrícia M.; Vaz, Pedro D.; Ribeiro-Claro, Paulo J. A.

2012-11-01

153

Multidimensional local mode calculations for the vibrational spectra of OH(-)(H2O)2 and OH(-)(H2O)2·Ar.  

PubMed

Multidimensional local mode calculations are performed for OH stretching vibrations of the gas phase OH(-)(H2O)2 and OH(-)(H2O)2·Ar clusters in the 1000-4000 cm(-1) energy range. The potential energies and the associated dipole moment values are calculated with MP2/6-311++G(3df,3pd). To fully take into account the anharmonic effects for the stretching vibrations of the ionic hydrogen bonded OHs (IHB OHs), those donating H to the O atom in OH(-), the vibrational Hamiltonian represented by the discrete variable representation (DVR) technique is diagonalized without using any truncation/contraction scheme for the basis. The necessary potential energies and dipole moment values at the DVR grid points are supplied by the polynomial inter- and extrapolations based on the values calculated at fine spatial grid points. We found that the peaks at 2700 cm(-1) should be assigned to the first overtone (?: 0 ? 2) of the IHB OH stretching vibrations rather than the previous assignment of the fundamental of the IHB OH based on harmonic frequencies. The relevant fundamental peaks should be observed around 1600-2000 cm(-1) where no experimental observation has been performed. This prediction of the fundamental peak positions leads to a simple correlation between the magnitude of the red-shift of the IHB OH stretching vibrational peak position and the cluster size of OH(-)(H2O)n for n = 1-3. Furthermore, to determine important contributions toward the assignment of the experimental spectrum, detailed analyses are performed from the following 3 viewpoints: (1) mode coupling between the inter water IHB OH stretching vibrations, (2) coupling between the IHB OH and the low-frequency OO stretching vibrations and (3) argon attachment to OH(-)(H2O)2. We found that the overall shape of the vibrational spectrum can be essentially described by considering only factor (1). However, fairly large peak shifts are caused by factors (2) and (3). PMID:23912845

Morita, Masato; Takahashi, Kaito

2013-09-28

154

Large scale variational calculations on the vibrational level structure and vibrational mixing in S0 HDCO up to very high excitation energies  

NASA Astrophysics Data System (ADS)

We perform converged high precision variational calculations to determine the exact energies of all vibrational states in S0 HDCO, extending up to 10 000 cm-1 of vibrational excitation energy. We also explore the resonances and intermode couplings in this energy range. We compare the calculated level structure to the recently measured frequencies by Ellsworth et al. [K.K. Ellsworth, B.D. Lajiness, J.P. Lajiness and W.F. Polik, J. Mol. Spectrosc. 252 (2008) 205] in order to check their assignments and further clarify the vibrational mixing pattern and vibrational resonances in HDCO, that are very different from the other more symmetric formaldehyde species H2CO and D2CO. For the calculations we use our specific vibrational method (recently employed for extensive vibrational studies on H2CO and D2CO), consisting of a combination of a search/selection algorithm and a Lanczos iteration procedure and based on the Martin, Lee, Taylor potential energy surface for formaldehyde, allowing to extend the calculations up to very high vibrational excitation energies.

Rashev, Svetoslav; Moule, David C.

2013-04-01

155

Vibrational spectra and ab initio molecular orbital calculations of the novel anti-cancer drug combretastatin A-4 prodrug  

NASA Astrophysics Data System (ADS)

The NIR-FT Raman and FT-IR spectral studies of the novel antineoplastic and antiangiogenesis substance comprestatin A-4 prodrug (CA4P) were carried out. The equilibrium geometry, various bonding features and harmonic vibrational frequencies of CA4P have been investigated with the help of B3LYP density functional theory (DFT) method. The most preferred cis-configuration for its bioactivity has been demonstrated on the basis of torsional potential energy surface (PES) scan studies. Stability of the molecule arising from hyperconjugative interactions leading to its bioactivity, charge delocalization and mesomeric effects have been analyzed using natural bond orbital (NBO) analysis. Detailed assignments of the vibrational spectra have been made with the aid of theoretically predicted vibrational frequencies. The optimized geometry shows near-planarity of phenyl rings and perpendicular conformation of meta substituted methoxy group. The vibrational analysis confirms the differently acting ring modes, steric repulsion, ? conjugation and back-donation.

James, C.; Pettit, G. R.; Nielsen, O. F.; Jayakumar, V. S.; Joe, I. Hubert

2008-10-01

156

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

NASA Astrophysics Data System (ADS)

The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S1(?,?*) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S0 and S1(?,?*) electronic states. In each case the decreased ? bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S0 and S1(?,?*) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S1(?,?*) excited state.

Shin, Hee Won; Ocola, Esther J.; Kim, Sunghwan; Laane, Jaan

2014-01-01

157

Design requirements and calculated performance of an XUV FEL oscillator operating on a higher harmonic  

NASA Astrophysics Data System (ADS)

We study, using numerical simulation methods, the design requirements for the electron beam, wiggler, and optical resonator of an extreme-ultraviolet (XUV, 100 ? ? ? 10 nm) free electron laser oscillator operating on a higher harmonic. Our previous theoretical studies of an XUV FEL oscillator have assumed operation at the fundamental wavelength. Higher-harmonic operation is attractive because the energy of the electrons can be reduced, thus reducing the cost of the linac. A further reduction in beam energy is possible with the use of short-period wigglers: in the present work, we use the expected properties of pulsed-wire wigglers. Operation of a FEL oscillator on the third harmonic has been experimentally demonstrated at Stanford University and Los Alamos, and this mode of operation may also be both possible and desirable for an XUV device.

John, Goldstein C.; Roger, Warren W.; Brian, Newnam E.

1991-07-01

158

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

159

Dispersion corrected DFT approaches for anharmonic vibrational frequency calculations: nucleobases and their dimers.  

PubMed

Computational spectroscopy techniques have become in the last few years an effective means to analyze and assign infrared (IR) spectra of molecular systems of increasing dimensions and in different environments. However, transition from compilation of harmonic data to fully anharmonic simulations of spectra is still underway. The most promising results for large systems have been obtained, in our opinion, by perturbative vibrational approaches based on potential energy surfaces computed by hybrid (especially B3LYP) density functionals and medium size (e.g. SNSD) basis sets. In this framework, we are actively developing a comprehensive and robust computational protocol aimed at quantitative reproduction of the spectra of nucleic acid base complexes and their adsorption on solid supports (organic/inorganic). In this contribution we report the essential results of the first step devoted to isolated monomers and dimers. It is well known that in order to model the vibrational spectra of weakly bound molecular complexes dispersion interactions should be taken into proper account. In this work we have chosen two popular and inexpensive approaches to model dispersion interactions, namely the semi-empirical dispersion correction (D3) and pseudopotential based (DCP) methodologies both in conjunction with the B3LYP functional. These have been used for simulating fully anharmonic IR spectra of nucleobases and their dimers through generalized second order vibrational perturbation theory (GVPT2). We have studied, in particular, isolated adenine, hypoxanthine, uracil, thymine and cytosine, the hydrogen-bonded and stacked adenine and uracil dimers, and the stacked adenine-naphthalene heterodimer. Anharmonic frequencies are compared with standard B3LYP results and experimental findings, while the computed interaction energies and structures of complexes are compared to the best available theoretical estimates. PMID:24531740

Fornaro, Teresa; Biczysko, Malgorzata; Monti, Susanna; Barone, Vincenzo

2014-06-01

160

Vibration  

NASA Technical Reports Server (NTRS)

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

Hornick, R. J.

1973-01-01

161

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

NSDL National Science Digital Library

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

Rawitscher, George

2011-07-31

162

Comparative vibrational spectroscopic studies, HOMO-LUMO, NBO analyses and thermodynamic functions of p-cresol and 2-methyl-p-cresol based on DFT calculations  

NASA Astrophysics Data System (ADS)

In the present study structural properties of p-cresol, and 2-methoxy-p-cresol have been studied by using B3LYP/cc-pvdz and B3PW91/cc-pvdz of Density Functional Theory (DFT) utilizing Becke three exchange functional and Lee Yang Paar correlation functional. The Fourier transform infrared and Fourier transform Raman spectra of title molecules were recorded (solid phase). Optimized geometry, harmonic vibrational frequencies and various thermodynamic parameters of the title compounds were calculated with B3LYP/cc-pvdz, and B3PW91/cc-pvdz basis sets. Non-linear optical (NLO) behavior of the p-cresol and 2-methoxy-p-cresol were investigated by determining of electric dipole moment, polarizability ?, and hyperpolarizability ? using the above mentioned basis sets. The molecular properties such as ionization potential, electronegativity, chemical potential, electrophilicity have been deduced from HOMO-LUMO analysis employing the same basis sets. A detailed interpretation of the infrared and Raman spectra of title molecules were reported. UV spectrum was measured in different solvent. The energy and oscillator strength are calculated by Time Dependant Density Functional Theory (TD-DFT) results. The calculated HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. The complete assignments were performed on the basis of the potential energy distribution (PED) of vibrational modes, calculated with scaled quantum mechanics (SQM) method. Finally the theoretical FT-IR, FT-Raman, and UV spectra of the title molecules have also been constructed.

Balachandran, V.; Murugan, M.; Nataraj, A.; Karnan, M.; Ilango, G.

2014-11-01

163

Comparative vibrational spectroscopic studies, HOMO-LUMO, NBO analyses and thermodynamic functions of p-cresol and 2-methyl-p-cresol based on DFT calculations.  

PubMed

In the present study structural properties of p-cresol, and 2-methoxy-p-cresol have been studied by using B3LYP/cc-pvdz and B3PW91/cc-pvdz of Density Functional Theory (DFT) utilizing Becke three exchange functional and Lee Yang Paar correlation functional. The Fourier transform infrared and Fourier transform Raman spectra of title molecules were recorded (solid phase). Optimized geometry, harmonic vibrational frequencies and various thermodynamic parameters of the title compounds were calculated with B3LYP/cc-pvdz, and B3PW91/cc-pvdz basis sets. Non-linear optical (NLO) behavior of the p-cresol and 2-methoxy-p-cresol were investigated by determining of electric dipole moment, polarizability ?, and hyperpolarizability ? using the above mentioned basis sets. The molecular properties such as ionization potential, electronegativity, chemical potential, electrophilicity have been deduced from HOMO-LUMO analysis employing the same basis sets. A detailed interpretation of the infrared and Raman spectra of title molecules were reported. UV spectrum was measured in different solvent. The energy and oscillator strength are calculated by Time Dependant Density Functional Theory (TD-DFT) results. The calculated HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. The complete assignments were performed on the basis of the potential energy distribution (PED) of vibrational modes, calculated with scaled quantum mechanics (SQM) method. Finally the theoretical FT-IR, FT-Raman, and UV spectra of the title molecules have also been constructed. PMID:24892532

Balachandran, V; Murugan, M; Nataraj, A; Karnan, M; Ilango, G

2014-11-11

164

FT-IR, FT-Raman, NMR and UV-vis spectra, vibrational assignments and DFT calculations of 4-butyl benzoic acid  

NASA Astrophysics Data System (ADS)

The solid phase FTIR and FT-Raman spectra of 4-butyl benzoic acid (4-BBA) have been recorded in the regions 400-4000 and 50-4000 cm -1, respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-311++G(d,p) as basis set. The vibrational frequencies were calculated for monomer and dimer by DFT method and were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. The infrared and Raman spectra were also predicted from the calculated intensities. 13C and 1H NMR spectra were recorded and 13C and 1H nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV-visible spectrum of the compound was recorded in the region 200-400 nm and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. The geometric parameters, energies, harmonic vibrational frequencies, IR intensities, Raman intensities, chemical shifts and absorption wavelengths were compared with the available experimental data of the molecule.

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

2012-01-01

165

Ab-initio calculations of Raman, IR-active vibrational modes in isotopically modified B 12 icosahedral clusters  

NASA Astrophysics Data System (ADS)

Computational calculations of Becke's three-parameter hybrid method using the LYP correlation functional (B3LYP) have been performed on (B 12H 12) 2- dodecaborane anions with different boron isotopic compositions. This was done in order to investigate isotopic dependence of vibrational spectral properties of B 12 icosahedra, and for comparison of the optical vibrational properties of the icosahedral molecule with the characteristics of inter- or intra-icosahedral optical phonon vibrational modes in boron-rich crystals.

Nogi, Naoyuki; Tanaka, Satoru

2006-09-01

166

Calculation of deformed double-folding potentials in the context of the generalized rotation-vibration model  

NASA Astrophysics Data System (ADS)

We present a procedure to calculate quite accurately double-folding potentials involving deformed densities. The calculations are performed in the context of the generalized rotation-vibration model, which is a general approach to describe rotations and vibrations of nuclear densities for heavy nuclei. The present method is appropriate for obtaining the coupling potentials intended for future applications in coupled-channel calculations. We compare our results with those obtained from other models usually assumed in coupled-channel analyses.

Morales Botero, D. F.; Chamon, L. C.; Carlson, B. V.

2014-05-01

167

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

168

Vibrationally resolved photoelectron imaging of Cu2H- and AgCuH- and theoretical calculations.  

PubMed

Vibrationally resolved photoelectron spectra have been obtained for Cu(2)H(-) and AgCuH(-) using photoelectron imaging at 355 nm. Two transition bands X and A are observed for each spectrum. The X bands in both spectra show the vibration progressions of the Cu-H stretching mode and the broad peaks of these progressions indicate significant structural changes from Cu(2)H(-) and AgCuH(-) to their neutral ground states. The A bands in the spectra of Cu(2)H(-) and CuAgH(-) show stretching progressions of Cu-Cu and Ag-Cu, respectively. The contours of these two progressions are pretty narrow, indicating relatively small structural changes from Cu(2)H(-) and AgCuH(-) to their neutral excited states. Calculations based on density functional theory indicate that the ground states of Cu(2)H(-) and AgCuH(-) and the first excited states of their neutrals are linear, whereas their neutral ground states are bent. The photoelectron detachment energies and vibrational frequencies from these calculations are in good agreement with the experimental observations. Especially, the theoretical predication of linear structures for the anions and the neutral excited states are supported by the spectral features of A bands, in which the bending modes are inactive. Comparisons among the vertical detachment energies of Cu(2)H(-), AgCuH(-), and their analogs help to elucidate electronic characteristics of coinage metal elements and hydrogen in small clusters. PMID:23388039

Xie, Hua; Li, Xiaoyi; Zhao, Lijuan; Liu, Zhiling; Qin, Zhengbo; Wu, Xia; Tang, Zichao; Xing, Xiaopeng

2013-02-28

169

Multi-input multi-output feedforward control of multi-harmonic gearbox vibrations using parallel adaptive notch filters in the principal component space  

NASA Astrophysics Data System (ADS)

Rotating mechanical systems such as gearbox are known to generate vibrations at specific frequencies. The generation of asymmetric frequency sidebands around gear meshing frequencies is typical of rotating systems, and often results in amplitude-modulated disturbances. In addition, when the angular speed of such systems exhibits small time variations, a frequency-modulation of the disturbance tones is observed. Such conditions may result in difficulties for feedforward active control systems based on short, finite impulse response control filters, as was observed by previous researchers. This is mainly due to the fact that the reference signal may not provide all the gear meshing frequencies and sidebands found in the disturbance. This work investigates adaptive notch filters in the principal component space to cancel multi-harmonic gearbox vibrations. Experimental results obtained with these adaptive notch filters show good control attenuations at targeted gearbox tones, without amplification of other closely located, unreferenced tones.

Pasco, Yann; Robin, Olivier; Bélanger, Pierre; Berry, Alain; Rajan, Srivatsa

2011-10-01

170

Comparison of DFT methods for molecular structure and vibration spectra of ofloxacin calculations  

NASA Astrophysics Data System (ADS)

Comparison of the performance of different density functional theory (DFT) methods at various basis sets in predicting molecular and vibration spectra of ofloxacin was reported. The methods employed in this study comprise six functionals, namely, mPW1PW91, HCTH, LSDA, PBEPBE, B3PW91 and B3LYP. Different basis sets including LANL2DZ, SDD, LANL2MB, 6-31g, 6-311g and 3-21g were also examined. Comparison between the calculated and experimental data indicates that the mPW1PW91/6-311g level afford the best quality to predict the structure of ofloxacin. The results also indicate that B3LYP/LANL2DZ level show better performance in the vibration spectra prediction of ofloxacin than other DFT methods.

Yang, Yue; Gao, Hongwei

2012-01-01

171

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

NASA Technical Reports Server (NTRS)

The second-order Moller-Plesset ab initio electronic structure method is used to compute points for the anharmonic mode-coupled potential energy surface of N-methylacetamide (NMA) in the trans(sub ct) configuration, including all degrees of freedom. The vibrational states and the spectroscopy are directly computed from this potential surface using the Correlation Corrected Vibrational Self-Consistent Field (CC-VSCF) method. The results are compared with CC-VSCF calculations using both the standard and improved empirical Amber-like force fields and available low temperature experimental matrix data. Analysis of our calculated spectroscopic results show that: (1) The excellent agreement between the ab initio CC-VSCF calculated frequencies and the experimental data suggest that the computed anharmonic potentials for N-methylacetamide are of a very high quality; (2) For most transitions, the vibrational frequencies obtained from the ab initio CC-VSCF method are superior to those obtained using the empirical CC-VSCF methods, when compared with experimental data. However, the improved empirical force field yields better agreement with the experimental frequencies as compared with a standard AMBER-type force field; (3) The empirical force field in particular overestimates anharmonic couplings for the amide-2 mode, the methyl asymmetric bending modes, the out-of-plane methyl bending modes, and the methyl distortions; (4) Disagreement between the ab initio and empirical anharmonic couplings is greater than the disagreement between the frequencies, and thus the anharmonic part of the empirical potential seems to be less accurate than the harmonic contribution;and (5) Both the empirical and ab initio CC-VSCF calculations predict a negligible anharmonic coupling between the amide-1 and other internal modes. The implication of this is that the intramolecular energy flow between the amide-1 and the other internal modes may be smaller than anticipated. These results may have important implications for the anharmonic force fields of peptides, for which N-methylacetamide is a model.

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

2001-01-01

172

Energy Transfer Processes in Monochromatically Excited Iodine. IX. Classical Trajectory and Semiclassical Calculations of Vibrationally and Rotationally Inelastic Cross Sections.  

National Technical Information Service (NTIS)

Classical trajectory calculations were carried out on the system in which I2 in the triplet pi(0)(u+) excited electronic state and certain specific vibrational and rotational levels interact with the inert gases as collision partners. The trajectory resul...

M. Rubinson B. Garetz J. I. Steinfeld

1973-01-01

173

Time-dependent density-functional-theory calculation of high-order-harmonic generation of H2  

NASA Astrophysics Data System (ADS)

The observation of the isotope effect in the high-order-harmonic generation (HHG) of H2 presents a challenge for time-dependent density-functional-theory (TDDFT) methods, since this effect is related to the dynamics of the ion created in the tunneling ionization step of HHG and it depends on the harmonic order. As an initial step toward describing this effect within current computational capacity, we benchmark a method in which the nuclear and electronic degrees of freedom are separated and both treated quantum mechanically. For the electrons two TDDFT formalisms are adopted. Although the ion-dynamics effect is not described in our method, it reproduces the measured D2-to-H2 HHG ratios up to the 25th harmonic when the 35th is the classical cutoff. Beyond the 25th harmonic, however, our results show substantial deviation and are sensitive to the laser intensity. A higher intensity reproduces the experimental results. Analysis reveals an R-dependent phase factor as the cause of the isotope effect in our calculation. We isolate this phase factor and propose a strong-field-approximation-phase model, which reproduces experimental data, including those for which the ion-dynamics model has to be further modified. We show that the model that we propose is intrinsically related to the ion-dynamics model. Our model provides a correction to the TDDFT approach when the ion-dynamics effect becomes significant. It also indicates that the isotope effect is not only a probe for the ion created by the external field but is ultimately a more useful probe for the ground-state nuclear wave function. For all molecules whose vertical ionization potential strongly depends on the nuclear geometry, HHG may serve as a sensitive ultrafast probe of nuclear dynamics.

Chu, Xi; Groenenboom, Gerrit C.

2012-05-01

174

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

175

Structural, electronic, thermodynamical and charge transfer properties of Chloramphenicol Palmitate using vibrational spectroscopy and DFT calculations  

NASA Astrophysics Data System (ADS)

The global problem of advancing bacterial resistance to newer drugs has led to renewed interest in the use of Chloramphenicol Palmitate (C27H42Cl2N2O6) [Palmitic acid alpha ester with D-threo-(-),2-dichloro-N-(beta-hydroxy-alpha-(hydroxymethyl)-p-nitrophenethyl)acetamide also known as Detereopal]. The characterization of the three polymorphic forms of Chloramphenicol Palmitate (CPP) was done spectroscopically by employing FT-IR and FT-Raman techniques. The equilibrium geometry, various bonding features, and harmonic wavenumbers have been investigated for most stable form A with the help of DFT calculations and a good correlation was found between experimental data and theoretical values. Electronic properties have been analyzed employing TD-DFT for both gaseous and solvent phase. The theoretical calculation of thermodynamical properties along with NBO analysis has also been performed to have a deep insight into the molecule for further applications.

Mishra, Rashmi; Srivastava, Anubha; Sharma, Anamika; Tandon, Poonam; Baraldi, Cecilia; Gamberini, Maria Christina

2013-01-01

176

Vibrational infrared spectrum of NH 3 adsorbed on MgO(100). I. Ab initio calculations  

NASA Astrophysics Data System (ADS)

The perturbed cluster approach, previously devoted to the calculation of the stable adsorption site and energy for ammonia adsorbed on MgO(100), is used to determine the frequency and the intensity of the main peaks associated with the normal vibrational modes of the admolecule. The ab initio model based on a cluster embedded in an array of point charges is then compared to the perturbed cluster approach and used to investigate different molecular orientations and associations on the surface in order to give an interpretation to the occurrence of the infrared signals. Six normal modes for each admolecule are calculated due to the removing of internal degeneracy by adsorption. The characteristics of the calculated spectrum are compared to the experimental infrared data and it is shown that the set of selected situations is able to explain almost every band in the spectrum without implication of NH 3 dissociation on the surface.

Allouche, A.; Corà, F.; Girardet, C.

1995-12-01

177

Vibrational investigation on FT-IR and FT-Raman spectra, IR intensity, Raman activity, peak resemblance, ideal estimation, standard deviation of computed frequencies analyses and electronic structure on 3-methyl-1,2-butadiene using HF and DFT (LSDA\\/B3LYP\\/B3PW91) calculations  

Microsoft Academic Search

FT-IR and FT-Raman (4000–100cm?1) spectral measurements of 3-methyl-1,2-butadiene (3M12B) have been attempted in the present work. Ab-initio HF and DFT (LSDA\\/B3LYP\\/B3PW91) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, IR intensities and Raman activities. Complete vibrational assignments on the observed spectra are made with vibrational frequencies obtained by HF and DFT (LSDA\\/B3LYP\\/B3PW91) at 6-31G(d,p) and 6-311G(d,p) basis

S. Ramalingam; A. Jayaprakash; S. Mohan; M. Karabacak

2011-01-01

178

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

179

Rotational and Vibrational Kinetic Energies Should be Included in Mass-Energy Calculations  

NASA Astrophysics Data System (ADS)

Conversion of mass to energy involves more than rest mass. At the subatomic, nuclear, atomic and molecular levels there are rotational, spin and vibratory kinetic energies although small may account for some discrepancies between theory and experiment. In pair annhilation spin and vibratory kinetic energies should be included in calculations. Thus, [ E0= 2m0c^2 + .5I 2?rp+ .52?re+ (n + 1/2) ?vp+ (n + 1/2) ?ve+ 1/2mv^2p+ 1/2mv^2e] if the positron and electron are going slowly. The ?r and the ?v are the rotational angular velocity iand vibrational angular frequency. The mass energy equation for a nucleus and a molecule is therefore [E0= m0c^2 +1/2I?r^2 + (n +1/2)?v+ 1/2mv^2]. On a universal scale planets, stars, galaxies and galactic groups will have rotational Orbital and vibrational factors which should be included in any mass-energy conversions. Some of the energy attributed to binding energy on a nuclear level may actually be vibrational and rotational kinetic energy.

Brekke, Stewart

2007-03-01

180

Quantum calculations of vibrational energies of H3O2- on an ab initio potential.  

PubMed

We report a full-dimensional potential energy surface for H3O2-, based on fitting 66,965 ab initio electronic energies. A major feature of this potential is a barrier of roughly 200 cm-1 to internal rotation of the two hydroxyl groups about a line connecting the two oxygen atoms and the bridging hydrogen atom. The potential is used in calculations of vibrational energies, performed with the "Reaction Path" version of the code "MULTIMODE". The results are compared to recent infrared messenger experiments and are used to propose interpretations of the experimental results. PMID:15099067

Huang, Xinchuan; Braams, Bastiaan J; Carter, Stuart; Bowman, Joel M

2004-04-28

181

Calculation of damping rates in thin inhomogeneous ferromagnetic films due to coupling to lattice vibrations  

NASA Astrophysics Data System (ADS)

This article describes calculations of ferromagnetic resonance damping rates due to coupling between the magnetization and lattice vibrations through inhomogeneities. The mechanisms we have explored include generation of shear phonons through inhomogeneous anisotropy and generation of both longitudinal and shear phonons through inhomogeneous magnetostriction. In both cases, inhomogeneities couple the uniform precession to finite wave vector phonons. For both coupling mechanisms, the predicted damping rate is on the order of 106 s-1 in transition metals. The damping rate by these mechanisms is inversely proportional to the fifth power of the shear phonon velocity, and may play a significant role in mechanically softer materials such as magnet/polymer nanocomposites.

McMichael, R. D.; Kunz, Andrew

2002-05-01

182

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

183

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

184

Corrections to vibrational transition probabilities calculated from a three-dimensional model.  

NASA Technical Reports Server (NTRS)

Corrections to the collision-induced vibration transition probability calculated by Hansen and Pearson from a three-dimensional semiclassical model are examined. These corrections come from the retention of higher order terms in the expansion of the interaction potential and the use of the actual value of the deflection angle in the calculation of the transition probability. It is found that the contribution to the transition cross section from previously neglected potential terms can be significant for short range potentials and for the large relative collision velocities encountered at high temperatures. The correction to the transition cross section obtained from the use of actual deflection angles will not be appreciable unless the change in the rotational quantum number is large.

Stallcop, J. R.

1972-01-01

185

Vibrational Spectra and Density Functional Theory Calculations of Metallo-tetra-(tert-butyl)-tetra-azaporphyrines  

NASA Astrophysics Data System (ADS)

The infrared absorption and 514.5 nm excited Raman spectra were measured for the metallo-tetra-(tert-butyl)-tetraazaporphyrin (MT(tBu)TAP, M=Cu, Co, Ni, Zn). The ground-state structures and vibrational spectra of MT(tBu)TAPs have been calculated at the B3LYP level of theory. The observed Raman and IR bands have been assigned based on the calculation results and by comparing with the normal metalloporphyrins. The relationship between the Raman/IR frequencies and the structures of TAP ring was investigated. The results show that the frequencies of C?C?' stretch (Ag), asymmetric C?Nm stretch (Ag), and symmetric C?Nm stretch (Bg) modes increase linearly with the decrease of the core-sizes of TAP ring. Among the three modes, the later two are more sensitive to the core-size change.

Lu, Tong-tong; Gao, Hui-ling; He, Tian-jing; Liu, Fan-chen; Chen, Dong-ming

2010-10-01

186

A comparison of array element surface vibration calculated by finite element modelling and laser interferometer measurements  

Microsoft Academic Search

For several years the standard in ultrasound imaging has been second harmonic imaging. Recently, a new imaging modality dubbed super harmonic imaging (SHI) was proposed. SHI uses the higher - third to fifth - harmonics produced by either nonlinear propagation or contrast agent response. This modality requires a transducer with a high bandwidth (>130%), which was achieved by choosing different

P. L. M. J. van Neer; G. Matte; P. Gatta; M. Pappalardo; N. de Jong

2008-01-01

187

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

NASA Astrophysics Data System (ADS)

Orbital-optimized coupled-electron pair theory [or simply ``optimized CEPA(0),'' OCEPA(0), for short] and its analytic energy gradients are presented. For variational optimization of the molecular orbitals for the OCEPA(0) method, a Lagrangian-based approach is used along with an orbital direct inversion of the iterative subspace algorithm. The cost of the method is comparable to that of CCSD [O(N6) scaling] for energy computations. However, for analytic gradient computations the OCEPA(0) method is only half as expensive as CCSD since there is no need to solve the ?2-amplitude equation for OCEPA(0). The performance of the OCEPA(0) method is compared with that of the canonical MP2, CEPA(0), CCSD, and CCSD(T) methods, for equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions between radicals. For bond lengths of both closed and open-shell molecules, the OCEPA(0) method improves upon CEPA(0) and CCSD by 25%-43% and 38%-53%, respectively, with Dunning's cc-pCVQZ basis set. Especially for the open-shell test set, the performance of OCEPA(0) is comparable with that of CCSD(T) (?R is 0.0003 A? on average). For harmonic vibrational frequencies of closed-shell molecules, the OCEPA(0) method again outperforms CEPA(0) and CCSD by 33%-79% and 53%-79%, respectively. For harmonic vibrational frequencies of open-shell molecules, the mean absolute error (MAE) of the OCEPA(0) method (39 cm-1) is fortuitously even better than that of CCSD(T) (50 cm-1), while the MAEs of CEPA(0) (184 cm-1) and CCSD (84 cm-1) are considerably higher. For complete basis set estimates of hydrogen transfer reaction energies, the OCEPA(0) method again exhibits a substantially better performance than CEPA(0), providing a mean absolute error of 0.7 kcal mol-1, which is more than 6 times lower than that of CEPA(0) (4.6 kcal mol-1), and comparing to MP2 (7.7 kcal mol-1) there is a more than 10-fold reduction in errors. Whereas the MAE for the CCSD method is only 0.1 kcal mol-1 lower than that of OCEPA(0). Overall, the present application results indicate that the OCEPA(0) method is very promising not only for challenging open-shell systems but also for closed-shell molecules.

Bozkaya, U?ur; Sherrill, C. David

2013-08-01

188

Brueckner-Hartree-Fock Calculations of Spherical Nuclei in a Harmonic-Oscillator Basis. II  

Microsoft Academic Search

An approximation made in previous Brueckner-Hartree-Fock calculations is removed. Both the hole-hole and the particle-hole matrix elements of the single-nucleon potential are now calculated with the correct available energy of the pair. It is shown that, with a given G matrix, the occupied states and energies do not depend on the prescription used for the particle-particle elements. The formalism is

K. T. Davies; M. Baranger

1970-01-01

189

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

190

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

NASA Technical Reports Server (NTRS)

The vibrational frequencies and infrared intensities of naphthalene neutral and cation are studied at the self-consistent-field (SCF), second-order Moller-Plesset (MP2), and density functional theory (DFT) levels using a variety of one-particle basis sets. Very accurate frequencies can be obtained at the DFT level in conjunction with large basis sets if they are scaled with two factors, one for the C-H stretches and a second for all other modes. We also find remarkably good agreement at the B3LYP/4-31G level using only one scale factor. Unlike the neutral PAHs where all methods do reasonably well for the intensities, only the DFT results are accurate for the PAH cations. The failure of the SCF and MP2 methods is caused by symmetry breaking and an inability to describe charge delocalization. We present several interesting cases of symmetry breaking in this study. An assessment is made as to whether an ensemble of PAH neutrals or cations could account for the unidentified infrared bands observed in many astronomical sources.

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

1996-01-01

191

Lifetime of vibrational levels from Fourier grid calculations: RbCs example.  

PubMed

We present systematic calculations of the lifetimes of vibrational levels of excited Rb(5s)Cs(6p(1/2)) 0(+) electronic states. We show that a precise description of the variation with the internuclear distance of the transition dipole moment between electronic states is essential. It is also crucial to account precisely for the spin-orbit coupling between the Rb(5s)Cs(6p) A?(1)?(+) and b?(3)? states. We describe the general trends of the probability of formation of stable molecules in the Rb(5s)Cs(6s) X?(1)?(+) and a?(3)?(+) electronic states, through radiative decay from the 0(+)v' levels, together with the branching ratios for the obtention of singlet or triplet molecules, stable with respect to dissociation. Furthermore, this analysis allows us to demonstrate the efficiency of the Mapped Fourier Grid Hamiltonian Representation method (MFGHR) to determine rigorously the energy variation, throughout the continuous part of the spectrum, of the density of an observable connecting bound vibrational levels and continuum states. The resolution in energy can be adapted to the studied problem through a judicious choice of the grid parameters. PMID:21971363

Londoño, B E; Mahecha, J; Luc-Koenig, E; Crubellier, A

2011-11-14

192

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

193

Limits on high-order harmonic generation from single-atom calculations.  

National Technical Information Service (NTIS)

In the quantum mechanical calculations of electron and photon emission from atoms in strong laser fields we have employed a single-active-electron (SAE) model. We determine the effect of the time varying electric field of the laser on each of the valence ...

K. C. Kulander K. J. Schafer

1993-01-01

194

Structural, vibrational, electronic and NMR spectral analysis of 3-chloro-6-methoxypyridazine by DFT calculations  

NASA Astrophysics Data System (ADS)

In this work, the FT-Raman and FT-Infrared spectra of 3-chloro-6-methoxypyridazine sample were measured to elucidate the spectroscopic properties of title molecule in the spectral range of 3500-50 cm-1 and 4000-400 cm-1, respectively. The molecular geometry and vibrational frequencies of 3-chloro-6-methoxypyridazine in the ground state were calculated using the DFT/B3LYP/6-31G(d),6-311G(d,p) level. The recorded FT-IR and FT-Raman spectral measurements favor the calculated structural parameters which are further supported by spectral simulation. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The UV-Visible absorption spectrum of the compound that dissolved in methanol was recorded in the range of 800-200 nm. The formation of hydrogen bond and the most possible interaction are explained using natural bond orbital (NBO) analysis. The isotropic chemical shift computed by 13C and 1H NMR analysis also shows good agreement with experimental observations. In addition, the molecular electrostatic potential (MEP) and frontier molecular orbitals (FMOs) analysis of the title compound were investigated using theoretical calculations.

Vijaya Chamundeeswari, S. P.; James Jebaseelan Samuel, E.; Sundaraganesan, N.

2013-06-01

195

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

NASA Astrophysics Data System (ADS)

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

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

1998-11-01

196

Efficient and robust calculation of femtoscopic correlation functions in spherical harmonics directly from the raw pairs measured in heavy-ion collisions  

NASA Astrophysics Data System (ADS)

We present the formalism for calculating the femtoscopic correlation function directly in spherical harmonics. The numerator and denominator are stored as a set of one-dimensional histograms representing the spherical harmonic decompositions of each. We present the formalism to calculate the correlation function from them directly, without going to any three-dimensional histogram. We discuss the practical implementation of the method and we provide an example of its use. We also discuss the stability of the method in the presence of angular holes in the underlying data (e.g., from experimental acceptance).

Kisiel, A.; Brown, D. A.

2009-12-01

197

Molecular structure, anharmonic vibrational analysis and electronic spectra of o-, m-, p-iodonitrobenzene using DFT calculations  

NASA Astrophysics Data System (ADS)

In the present work, molecular geometry and anharmonic vibrational spectra of o-, m-, p-iodonitrobenzene have been studied. The anharmonic frequencies were calculated using second order perturbative (PT2) approach with basis set 3-21G? on iodine and 6-311G(d,p) on other atoms at DFT(B3LYP) level of theory and were compared to experimental values. The assignments of vibrational modes of isomeric iodonitrobenzenes were done by using potential energy distribution (PED) and vibrational assignments of benzene, nitrobenzene and iodobenzene. The combination and overtone bands are also assigned. The electronic spectra were recorded as well as simulated using polarizable continuum model (PCM) at TD-B3LYP/6-311G(d,p)/3-21G? level of theory. The vibrational and electronic spectra are interpreted. Moreover, atomic charges, MEP mapping, HOMO-LUMO, NBO analysis and various thermodynamics and molecular properties are reported.

Alam, Mohammad Jane; Ahmad, Shabbir

2014-02-01

198

A rigorous full-dimensional quantum dynamics calculation of the vibrational energies of H3O2-  

NASA Astrophysics Data System (ADS)

The vibrational energy levels of the H3O2- anion have been calculated using a rigorous quantum dynamics method based on an accurate ab initio potential energy surface. The eigenvalue problem is solved using the two-layer Lanczos iterative diagonalization algorithm in a mixed grid/nondirect product basis set, where the system Hamiltonian is expressed in a set of orthogonal polyspherical coordinates. The lowest 312 vibrational energy levels in each inversion symmetry, together with a comparison of fundamental frequencies with previous quantum dynamics calculations, are reported. Finally, a statistical analysis of nearest level spacing distribution is carried out, revealing a strongly chaotic nature.

Yu, Hua-Gen

2006-11-01

199

FT-IR and FT-Raman spectra and vibrational investigation of 4-chloro-2-fluoro toluene using ab initio HF and DFT (B3LYP/B3PW91) calculations  

NASA Astrophysics Data System (ADS)

FT-IR (4000-100 cm -1) and FT-Raman (4000-100 cm -1) spectra of solid sample of 4-chloro-2-fluoro toluene (4Cl2FT) have been recorded using Bruker IFS 66 V spectrometer. Ab initio-HF (HF/6-311++G (d, p)) and DFT (B3LYP/6-311++G and B3PW91/6-311++G (d, p)) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, IR intensities, Raman activities. The vibrational frequencies are calculated and scaled values are compared with FT-IR and FT-Raman experimental values. The isotropic HF and DFT analyses showed good agreement with experimental observations. The differences between the observed and scaled wave number values of most of the fundamentals are very small in B3LYP than HF. Comparison of the simulated spectra provides important information about the ability of the computational method (B3LYP) to describe the vibrational modes. The influences of substitutions on the geometry of molecule and its normal modes of vibrations have also been discussed. The changes made by substitutions on the benzene are much responsible for the non-linearity of the molecule. This is an attractive entity for the future studies of non-linear optics.

Ramalingam, S.; Periandy, S.; Elanchezhian, B.; Mohan, S.

2011-01-01

200

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

201

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

NASA Astrophysics Data System (ADS)

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

Gökce, Halil; Bahçeli, Semiha

2013-11-01

202

Vibrational spectra, DFT quantum chemical calculations and conformational analysis of P-iodoanisole  

NASA Astrophysics Data System (ADS)

The solid phase FT-IR and FT-Raman spectra of P-iodoanisole (P-IA) have been recorded in the regions 400-4000 and 50-4000 cm-1, respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by ab initio (HF) and density functional theory (B3LYP) methods with LanL2DZ as basis set. The potential energy surface scan for the selected dihedral angle of P-IA has been performed to identify stable conformer. The optimized structure parameters and vibrational wavenumbers of stable conformer have been predicted by density functional B3LYP method with LanL2DZ (with effective core potential representations of electrons near the nuclei for post-third row atoms) basis set. The nucleophilic and electrophilic sites obtained from the molecular electrostatic potential (MEP) surface were calculated. The temperature dependence of thermodynamic properties has been analyzed. Several thermodynamic parameters have been calculated using B3LYP with LanL2DZ basis set.

Arivazhagan, M.; Anitha Rexalin, D.; Geethapriya, J.

2013-09-01

203

The state averaged multiconfigurational time-dependent Hartree approach: vibrational state and reaction rate calculations.  

PubMed

The multiconfigurational time-dependent Hartree (MCTDH) approach uses optimized sets of time-dependent basis functions, called single-particle functions, to represent multidimensional wavefunctions and thereby facilitates efficient multidimensional quantum dynamics studies. The single-particle function bases are usually optimized for a single wavefunction. Here, an approach is studied which utilizes a common single-particle function basis to represent several wavefunctions simultaneously, i.e., the single-particle function basis is constructed to result in an optimized averaged description of a number of wavefunctions. The approach can favorably be used to obtain eigenstates of Hamiltonians or to represent thermal ensembles. Test calculations studying the vibrational states of CH(3) and the thermal rate constant of the H+CH(4)-->H(2)+CH(3) reaction are presented. It is found that the required size of the single-particle functions basis does not increase when the number of wavefunctions described simultaneously is increased. As a consequence, the new approach offers an increased efficiency, e.g., for MCTDH rate constant calculations. PMID:18282029

Manthe, Uwe

2008-02-14

204

The state averaged multiconfigurational time-dependent Hartree approach: Vibrational state and reaction rate calculations  

NASA Astrophysics Data System (ADS)

The multiconfigurational time-dependent Hartree (MCTDH) approach uses optimized sets of time-dependent basis functions, called single-particle functions, to represent multidimensional wavefunctions and thereby facilitates efficient multidimensional quantum dynamics studies. The single-particle function bases are usually optimized for a single wavefunction. Here, an approach is studied which utilizes a common single-particle function basis to represent several wavefunctions simultaneously, i.e., the single-particle function basis is constructed to result in an optimized averaged description of a number of wavefunctions. The approach can favorably be used to obtain eigenstates of Hamiltonians or to represent thermal ensembles. Test calculations studying the vibrational states of CH3 and the thermal rate constant of the H+CH4-->H2+CH3 reaction are presented. It is found that the required size of the single-particle functions basis does not increase when the number of wavefunctions described simultaneously is increased. As a consequence, the new approach offers an increased efficiency, e.g., for MCTDH rate constant calculations.

Manthe, Uwe

2008-02-01

205

Calculation of the structures, stabilities, and vibrational spectra of arsenites, thioarsenites and thioarsenates in aqueous solution  

NASA Astrophysics Data System (ADS)

Structures, stabilities and vibrational spectra have been calculated using molecular quantum mechanical methods for As(OH) 3, AsO(OH) 3, As(SH) 3, AsS(SH) 3 and their conjugate bases and for several species with partial substitution of S for O. Properties for the neutral gas-phase molecules are calculated with state-of-the-art methods which yield As sbnd L distances within 0. 01 Å and As sbnd L stretching frequencies within 10 cm -1 of experiment. Similar accuracy is obtained for neutral molecules in solution using a polarizable continuum model (PCM). For monoanions such as AsO(OH)2- and AsS(SH)2-1 frequencies can be calculated to within 20 cm -1 of experiment using the polarizable continuum model. Multiply charged anions remain a challenge for accurate frequency calculations, but we have obtained results within the PCM model which at least semiquantitatively reproduce the available data. This allows us to assign the controversial features D, E and F in the Raman data of (Wood S. A., Tait C. D. and Janecky D. R. (2002) A Raman spectroscopic study of arsenite and thioarsenite species in aqueous solution at 25 °C. Geochem. Trans. 3, 31-39). To help in the assignment of the arsenic sulfide spectra we have also calculated energetics for the oxidation of As(III) to As(V) compounds by polysulfides, disproportionation of As(III) compounds and for the dissociation of the oxo- and thio-acids. We have determined that As(III) oxyacids can be transformed to thioacids which can in turn be oxidized to As(V) sulfides by polysulfides and that the p Ka1s of the acids involved can be ordered as follows: AsS(SH) 3 < As(SH) 3 < AsO(OH) 3 < As(OH) 3 in order of increasing p Ka1. We have also established from the calculated energies that the most stable form of the As(III) oxyacid in acidic aqueous solution is indeed As(OH) 3, consistent with previous assignments.

Tossell, J. A.; Zimmermann, M. D.

2008-11-01

206

Phonon vibrational frequencies of all single-wall carbon nanotubes at the Lambda point: Reduced matrix calculations  

Microsoft Academic Search

With a simple method—the reduced matrix method, we simplified the calculation of the phonon vibrational frequencies according to SWNTs structure and their phonon symmetric property and got the dispersion properties of all SWNTs at ? point in Brillouin zone, whose diameters lie between 0.6 and 2.5nm. The calculating time is shrunk about 2–4 orders. A series of the dependent relationships

Yufang Wang; Yanzhao Wu; Min Feng; Hui Wang; Qinghua Jin; Datong Ding; Xuewei Cao

2008-01-01

207

Molecular structure, harmonic and anharmonic frequency calculations of 2,4-dichloropyrimidine and 4,6-dichloropyrimidine by HF and density functional methods  

Microsoft Academic Search

Quantum chemical calculations of energies, geometrical structural parameters, harmonic and anharmonic frequencies of 2,4-DCP and 4,6-DCP were carried out by HF and density functional theory methods with 6-311++G(d,p) as basis set. The assignment of each normal mode has been made using the observed and calculated frequencies, their IR and Raman intensities. A detailed interpretation of the FT-IR and FT-Raman spectra

Usha Rani; Halil Oturak; S. Sudha; N. Sundaraganesan

2011-01-01

208

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

209

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

PubMed

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. PMID:20170236

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

2010-02-21

210

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

211

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

PubMed

The N-(4-nitrophenyl)-?-alanine in crystalline form directly by the addition of 4-nitroaniline to the acrylic acid in aqueous solution has been obtained. The title ?-alanine derivative crystallizes in the P2(1)/c space group of monoclinic system with four molecules per unit cell. The X-ray geometry of ?-alanine derivative molecule has been compared with those obtained by molecular orbital calculations corresponding to the gas phase. In the crystal the molecules related by an inversion center interact via symmetrically equivalent O-H···O hydrogen bonds with O···O distance of 2.656(2) Å forming a dimeric structure. The dimers of ?-alanine derivative weakly interact via N-H···O hydrogen bonds between the H atom of ?-amine groups and one of O atom of nitro groups. The room temperature powder vibrational (infrared and Raman) measurements are in accordance with the X-ray analysis. In aqueous solution of 4-nitroaniline and acrylic acid, the double CC bond of vinyl group of acrylic acid breaks as result of 4-nitroaniline addition. PMID:20980195

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

2011-08-15

212

The muonium adduct to biacetyl ab initio calculations and vibrational averaging  

NASA Astrophysics Data System (ADS)

The room temperature muon-electron hyperfine coupling constant of the 2-muoxy-3-ketobut-2-yl radical formed by Mu addition to biacetyl (butane-2,3-dione) is the smallest thus far measured in any radical, with A?_?˜eq 0.7 MHz (R.M. Macrae, C.J. Rhodes, K. Nishiyama and K. Nagamine, Chem. Phys. Lett, submitted). Calculations on this radical using the ROHF, UHF, and B/PW 91 formalisms are presented, with averaging performed over the C-O torsional mode using an expansion in free internal rotation eigenfunctions. UHF and B/PW 91 give similar predictions of the dependence of A?_? on the torsional angle ?, but are strikingly different in their predictions of the torsional energetics. This difference is traced to spin contamination in the UHF wavefunction. UHF disagrees with both ROHF and B/PW 91 in its structural predictions, yielding excessive electron delocalisation into the central C-C bond. Vibrational corrections lead to a small |A?_?| with a weak temperature-dependence, and suggest that the radical may twist from the trans geometry of the parent compound into the energetically more favourable intramolecularly H-bonded cis structure.

Macrae, R. M.; Briere, T. M.

1997-04-01

213

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

214

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

215

FT-IR and Raman spectra vibrational assignments and density functional calculations of 1-naphthyl acetic acid  

NASA Astrophysics Data System (ADS)

This work deals with the vibrational spectroscopy of 1-naphthyl acetic acid. The molecular vibrations of 1-naphthyl acetic acid (NAA) is investigated in polycrystalline sample, at room temperature, by Fourier transform infrared (FT-IR) and FT-Raman spectroscopy. In parallel, ab initio and various density functional (DFT) methods were used to determine the geometrical, energetic and vibrational characteristics of NAA. On the basis of B3LYP/6-311 + G** method and basis set combinations, a normal mode analysis was performed to assign the various fundamental frequencies according to the total energy distribution (TED). Simulation of infrared and Raman spectra, utilizing the results of these calculations led to excellent overall agreement with observed spectral patterns by refinement of scale factors.

Krishnakumar, V.; Mathammal, R.; Muthunatesan, S.

2008-06-01

216

Vibrational spectra of 2 (3H) benzofuranone studied by Raman, IR spectroscopy and AM1 semiempirical molecular orbital calculations  

NASA Astrophysics Data System (ADS)

Raman spectra of 2 (3H) benzofuranone have been recorded in the region 400-3200 cm -1and the IR spectra have been recorded in the region 200-4000 cm -1. Vibrational frequencies for the fundamental modes of this bicyclic heteroatomic molecule have also been calculated using Austin method 1 (AM1) semiempirical molecular orbital method. Vibrational assignments have been made for the fundamental modes and the observed combination and overtone bands are also assigned. A splitting in the carbonyl group(C?O stretching) frequency observed at 1640-1660 cm -1 in both Raman and IR spectra, is explained as Fermi-resonance. Net atomic charges for each atom of this molecule along with its heat of formation were also calculated. It is evident from the calculations that the 2 (3H) benzofuranone is more stable than the 3 (2H) benzofuranone in contrast to earlier estimates.

Pandey, V. K.; Singh, V. B.; Rai, Amareshwer K.; Asthana, B. P.; Rai, S. B.; Rai, D. K.

2003-01-01

217

Vibrational spectra of 2 (3H) benzofuranone studied by Raman, IR spectroscopy and AM1 semiempirical molecular orbital calculations.  

PubMed

Raman spectra of 2 (3H) benzofuranone have been recorded in the region 400-3200 cm(-1) and the IR spectra have been recorded in the region 200-4000 cm(-1). Vibrational frequencies for the fundamental modes of this bicyclic heteroatomic molecule have also been calculated using Austin method 1 (AM1) semiempirical molecular orbital method. Vibrational assignments have been made for the fundamental modes and the observed combination and overtone bands are also assigned. A splitting in the carbonyl group (C=O stretching) frequency observed at 1640-1660 cm(-1) in both Raman and IR spectra, is explained as Fermi-resonance. Net atomic charges for each atom of this molecule along with its heat of formation were also calculated. It is evident from the calculations that the 2 (3H) benzofuranone is more stable than the 3 (2H) benzofuranone in contrast to earlier estimates. PMID:12685893

Pandey, V K; Singh, V B; Rai, Amareshwer K; Asthana, B P; Rai, S B; Rai, D K

2003-01-15

218

Calculation of exact vibrational spectra for P2O and CH2NH using a phase space wavelet basis.  

PubMed

''Exact" quantum dynamics calculations of vibrational spectra are performed for two molecular systems of widely varying dimensionality (P2O and CH2NH), 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. PMID:24880271

Halverson, Thomas; Poirier, Bill

2014-05-28

219

Calculation of exact vibrational spectra for P2O and CH2NH using a phase space wavelet basis  

NASA Astrophysics Data System (ADS)

``Exact" quantum dynamics calculations of vibrational spectra are performed for two molecular systems of widely varying dimensionality (P2O and CH2NH), 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; Poirier, Bill

2014-05-01

220

Vibrational dispersion interactions in van der Waals complexes: Effect upon stability and infrared spectra  

Microsoft Academic Search

The vibrational analogue of London dispersion forces has been studied for a generalized bimolecular complex, and calculations have been performed for a series of van der Waals complexes comprised of subunits COâ, CâHâ, and HCN. The authors present a generalized nonempirical perturbational methodology for evaluating the second-order stabilization resulting from the correlation between instantaneous monomeric vibrational motions using the harmonic

William A. Glauser; M. L. Koszykowski

1991-01-01

221

Vibration of a beam on continuous elastic foundation with nonhomogeneous stiffness and damping under a harmonically excited mass  

NASA Astrophysics Data System (ADS)

In this paper, a method of analysis of a beam that is continuously supported on a linear nonhomogeneous elastic foundation and subjected to a harmonically excited mass is presented. The solution is obtained by decomposing the nonhomogeneous foundation properties and the beam displacement response into double Fourier summations which are solved in the frequency-wavenumber domain, from which the space-time domain response can be obtained. The method is applied to railway tracks with step variation in foundation properties. The validity of this method is checked, through examples, against existing methods for both homogeneous and nonhomogeneous foundation parameters. The effect of inhomogeneity and the magnitude of the mass are also investigated. It is found that a step variation in foundation properties leads to a reduction in the beam displacement and an increase in the resonance frequency for increasing step change, with the reverse occurring for decreasing step change. Furthermore, a beam on nonhomogeneous foundation may exhibit multiple resonances corresponding to the foundation stiffness of individual sections, as the mass moves through the respective sections along the beam.

Koroma, S. G.; Hussein, M. F. M.; Owen, J. S.

2014-04-01

222

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

NASA Astrophysics Data System (ADS)

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

Hahn, Sangjoon; Park, Kisam; Cho, Minhaeng

1999-09-01

223

Quantum calculations of vibrational energies of H3O2(-) and H5O2(+) with new ab initio potentials  

NASA Astrophysics Data System (ADS)

We have performed quantum mechanical studies of the vibrations of H3O2(-) and H5O2(+) in full dimensionality and with sufficient accuracy to resolve important features of the measured spectra. The computational procedure starts with extensive electronic structure calculations (several 10K configurations) at the CCSD(T) level of theory with augmented VTZ basis set using MOLPRO 2002. Then a global fit to the potential energy surface is constructed, based on a functional form that respects the spatial and permutational symmetries of the system. This PES fit is employed in a "Reaction Path Hamiltonian" MULTIMODE [1] calculation to obtain the vibrational spectrum. We provide comparisons with experimental data [2]. [1] MULTIMODE: A code to calculate rovibrational energies of polyatomic molecules, J. M. Bowman, S. Carter, and X.-C. Huang, Int. Rev. Phys. Chem. 22, 533 (2003). [2] Quantum calculations of vibrational energies of H3O2(-) with a new ab initio potential reveal large tunneling splittings. Manuscript in preparation, Dec 2003.

Huang, Xinchuan; Braams, Bastiaan J.; Carter, Stuart; Bowman, Joel M.

2004-03-01

224

An effective scaling frequency factor method for scaling of harmonic vibrational frequencies: The use of redundant primitive coordinates  

Microsoft Academic Search

A modified effective scaling frequency factor (ESFF) method that takes advantage of the potential energy distribution (PED) coefficients calculated in the basis of redundant primitive internal coordinates is presented. This approach is simpler and more flexible than that based on the natural internal coordinates. The sets of optimal scaling factors for routine 9- and 11-parameter ESFF calculations based on B3LYP\\/6-311G??

Piotr Borowski

2010-01-01

225

Structural and vibrational properties of ?-MoO3 from van der Waals corrected density functional theory calculations  

NASA Astrophysics Data System (ADS)

Structural and vibrational properties of ?-MoO3 are studied employing two recently proposed methodologies for incorporating van der Waals (vdW) contributions in density functional theory (DFT) based calculations. The DFT-D2 [S. Grimme, J. Comput. Chem.JCCHDD0192-865110.1002/jcc.20495 27, 1787 (2006)] and optB88 vdW-DFT [J. Klimeš , J. Phys.: Condens. MatterPRBMDO0953-898410.1088/0953-8984/22/2/022201 22, 022201 (2010)] methods are shown to give rise to increased accuracy in predicted lattice parameters, relative to conventional DFT methods. Calculated vibrational frequencies agree with measurements to within 5% and 10% for modes involving bonded and nonbonded interactions in this compound, respectively.

Ding, Hong; Ray, Keith G.; Ozolins, Vidvuds; Asta, Mark

2012-01-01

226

Elastic and vibrational properties of Mg2Si1-xSnx alloy from first principles calculations  

NASA Astrophysics Data System (ADS)

The structural, elastic and phonon properties of Mg2Si1-xSnx alloy are investigated by performing density functional theory and density functional perturbation theory calculations. The calculated lattice parameter increases with the increase of Sn content obeying Vegard's Law that is in good agreement with available experimental data. Shear modulus, Young's modulus and sound velocities are determined from the obtained elastic constants. Phonon dispersion curves show a pronounced softening with increasing of Sn content. The softening mechanism has been discussed based upon the element mass and bond strength. Besides, phonon contribution to the Helmholtz free energy, the entropy and the constant-volume heat capacity are calculated within the harmonic approximation based on the calculated phonon density of states. Results show Mg2Si1-xSnx is thermodynamically more stable with higher Sn content.

Peng, H.; Wang, C. L.; Li, J. C.; Wang, H. C.; Sun, Y.; Zheng, Q.

2012-05-01

227

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

PubMed

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

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

2014-05-01

228

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

229

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

230

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

231

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

232

Infrared spectra of Dewar 4-picoline in low-temperature argon matrices and vibrational analysis by DFT calculation  

NASA Astrophysics Data System (ADS)

Dewar 4-picoline produced by UV irradiation on 4-picoline in a low-temperature argon matrix was monitored by FT-IR spectroscopy. The observed infrared bands were assigned to an isomer which has a C-C bridging bond with the aid of DFT (density functional theory) calculation, where the 6-31++G ** basis set was used to optimize the geometrical structure. No other isomer bands were observed. A systematic comparison of the scaling factors derived from the observed and calculated wavenumbers for pyridine, 2-picoline, 4-picoline and their corresponding Dewar isomers indicates a linear relationship between the scaling factors and the vibrational wavenumbers.

Kudoh, Satoshi; Takayanagi, Masao; Nakata, Munetaka

2000-05-01

233

Full-wave calculation of sheared poloidal flow driven by high-harmonic ion Bernstein waves in tokamak plasmas  

SciTech Connect

A full-wave, one-dimensional spectral model is developed to study sheared poloidal flow driven by high-harmonic ion Bernstein waves (IBWs) in tokamak plasmas. The local plasma conductivity is corrected to lowest order in {rho}/L where {rho} is the ion Larmor radius and L is the equilibrium scale length. This correction takes into account gradients in equilibrium quantities and is necessary for conservation of energy. It is equivalent to the ''odd-order derivative'' terms in finite difference models. No assumption is made regarding the smallness of the ion Larmor radius relative to wavelength, and results are applicable to all orders in k{sub (perpendicular} {sub sign)}{rho} where k{sub (perpendicular} {sub sign)} is the perpendicular wave number. Previous numerical results for flow drive have relied on expansions in k{sub (perpendicular} {sub sign)}{rho}, and are thus limited to cyclotron harmonics of two and below. In this article, we consider higher-harmonic cases corresponding to recent IBW flow drive experiments on the Tokamak Fusion Test Reactor [B. P. LeBlanc, R. E. Bell, S. Bernabei et al., Phys. Rev. Lett. 82, 331 (1999)] and the Frascati Tokamak Upgrade [R. Cesario, C. Castaldo, V. Pericoli-Ridolfini et al., ''Recent Results of the Ion Bernstein Wave Heating Experiment on FTU,'' in Proceedings of the 13th Topical Conference on Radio Frequency Power in Plasmas, 1999, Annapolis, MD, edited by S. Bernabei and F. Paoletti (American Institute of Physics, New York, 1999), p. 100]. In these cases, a directly launched high-harmonic IBW is used to drive poloidal flow near the fourth- and fifth-harmonic ion cyclotron layers. Other applications include high-harmonic fast wave heating in low aspect ratio tokamaks such as the National Spherical Torus Experiment [S. M. Kaye, M. Ono, Y.-K. M. Peng et al., Fusion Technol. 36, 16 (1999)]. (c) 2000 American Institute of Physics.

Jaeger, E. F. [P.O. Box 2009, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8071 (United States)] [P.O. Box 2009, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8071 (United States); Berry, L. A. [P.O. Box 2009, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8071 (United States)] [P.O. Box 2009, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8071 (United States); Batchelor, D. B. [P.O. Box 2009, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8071 (United States)] [P.O. Box 2009, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8071 (United States)

2000-08-01

234

Full-wave calculation of sheared poloidal flow driven by high-harmonic ion Bernstein waves in tokamak plasmas  

NASA Astrophysics Data System (ADS)

A full-wave, one-dimensional spectral model is developed to study sheared poloidal flow driven by high-harmonic ion Bernstein waves (IBWs) in tokamak plasmas. The local plasma conductivity is corrected to lowest order in ?/L where ? is the ion Larmor radius and L is the equilibrium scale length. This correction takes into account gradients in equilibrium quantities and is necessary for conservation of energy. It is equivalent to the ``odd-order derivative'' terms in finite difference models. No assumption is made regarding the smallness of the ion Larmor radius relative to wavelength, and results are applicable to all orders in k?? where k? is the perpendicular wave number. Previous numerical results for flow drive have relied on expansions in k??, and are thus limited to cyclotron harmonics of two and below. In this article, we consider higher-harmonic cases corresponding to recent IBW flow drive experiments on the Tokamak Fusion Test Reactor [B. P. LeBlanc, R. E. Bell, S. Bernabei et al., Phys. Rev. Lett. 82, 331 (1999)] and the Frascati Tokamak Upgrade [R. Cesario, C. Castaldo, V. Pericoli-Ridolfini et al., ``Recent Results of the Ion Bernstein Wave Heating Experiment on FTU,'' in Proceedings of the 13th Topical Conference on Radio Frequency Power in Plasmas, 1999, Annapolis, MD, edited by S. Bernabei and F. Paoletti (American Institute of Physics, New York, 1999), p. 100]. In these cases, a directly launched high-harmonic IBW is used to drive poloidal flow near the fourth- and fifth-harmonic ion cyclotron layers. Other applications include high-harmonic fast wave heating in low aspect ratio tokamaks such as the National Spherical Torus Experiment [S. M. Kaye, M. Ono, Y.-K. M. Peng et al., Fusion Technol. 36, 16 (1999)].

Jaeger, E. F.; Berry, L. A.; Batchelor, D. B.

2000-08-01

235

Calculation of density functional theory (DFT) vibrational parameters of nucleotides for use in theoretical optical calculations: Herein applied to circular dichroism (CD) and absorption of polynucleotides  

NASA Astrophysics Data System (ADS)

The Vibrational Circular Dichroism (VCD) of Nucleic Acids is a sensitive function of their conformation. DeVoe's classically derived polarizability theory allows the calculation of polymer absorption and circular dichroism spectra in any frequency range. Following the approach of Tinoco and Cech as modified by Moore and Self, calculations were done in the infrared (IR) region with theoretically derived monomer input parameters. Presented herein are calculated absorption and CD spectra for nucleic acid oligomers and polymers. These calculations improve upon earlier attempts, which utilized frequencies, intensities and normal modes from empirical analysis of the nitrogenous base of the monomers. These more complete input polarizability parameters include all contributions to specific vibrational normal modes for the entire nucleotide structure. They are derived from density functional theory (DFT) vibrational analysis on quasi-nucleotide monomers using the GAUSSIAN '98/'03 program. The normal modes are "integrated" for the first time into single virtual (DeVoe) oscillators by incorporating "fixed partial charges" in the manner of Schellman. The results include the complete set of monomer normal modes. All of these modes may be analyzed, in a manner similar to those demonstrated here (for the 1500-1800 cm-1 region). A model is utilized for the polymer/oligomer monomers which maintains the actual electrostatic charge on the adjacent protonated phosphoryl groups (hydrogen phosphate, a mono-anion). This deters the optimization from "collapsing" into a hydrogen-bonded "ball" and thereby maintains the extended (polymer-like) conformation. As well, the precise C2 "endo" conformation of the sugar ring is maintained in the DNA monomers. The analogous C3 "endo" conformation is also maintained for the RNA monomers, which are constrained by massive "anchors" at the phosphates. The complete IR absorbance spectra (0-4,000 cm-1) are calculated directly in Gaussian. Calculated VCD and Absorbance Spectra for the eight standard Ribonucleic and Deoxy-ribonucleic acid homo-polymers in the nitrogenous base absorbing region 1550-1750 cm-1 are presented. These spectra match measured spectra at least as well as spectra calculated from empirical parameters. These results demonstrate that the purely theoretical calculation, an example given herein, should serve to provide more transferable, universal parameters for the polarizability treatment of the optical properties of oligomers and polymers.

Ferber, Steven Dwight

236

An approach to the interpretation of the vibrational spectra of 2?-deoxyinosine by means of DFT calculations  

NASA Astrophysics Data System (ADS)

The FT-IR and FT-Raman spectra of 2'-deoxyinosine (2'-dI) are reported. This modified nucleoside of the four natural DNA bases binds with weak hydrogen bonds to any of them, feature used in PCR technique or in hybridisation essays [Howard Huge Medical Institute]. The FT-IR and FT-Raman spectra of its synthesized trideuterated derivative (2'-dI-d 3, deuteration at N1, and hydroxyl groups O3' and O5') have also been recorded. The observed isotopic shifts, the spectra of related molecules and theoretical calculations have been used to interpret the vibrational spectra of 2'-dI. The accurate knowledge of the vibrational spectra is an important prerequisite for understanding its structure, conformation and possible behaviour in physiological conditions. Therefore, different optimised structures have been obtained, including variable number of water molecules (none, 1 or 2) surrounding the nucleoside. They have been situated close to the carbonyl group. The wavenumbers of the normal modes of vibration for each one have been calculated using Density Functional Theory methods, with the Becke's Three Parameter Hybrid Functional and the LYP Correlation Functional (B3LYP) model, using 6-31G** basis set. An assignment of FT-IR and Raman spectra is proposed. The influence of the water molecules in the theoretical results is shown.

de la Fuente, M.; Navarro, R.

2004-01-01

237

Molecular and vibrational structure of 2,4-dinitrophenol: FT-IR, FT-Raman and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

The molecular vibrations of 2,4-dinitrophenol (DNP) were investigated in polycrystalline sample, at room temperature, by Fourier transform infrared (FT-IR) and FT-Raman spectroscopies. In parallel, semiempirical, ab initio and various density functional theory (DFT) methods are used to determine the geometrical, energetic and vibrational characteristics of DNP. Both the experimental and theoretical data suggest a rather strong intramolecular H-bond (HB) involving the hydroxyl and its neighbor nitro group. Semiempirical PM3 and ab initio methods fail to describe the HB while among different exchange and correlation functionals used in conjunction with DFT methods, only the B3LYP combination is able to quantitatively reproduce the effects of intramolecular HB, as reflected in FT-IR and FT-Raman spectra. The vibrational experimental bands were assigned to normal modes on the basis of DFT calculations at the B3LYP/6-31G(d) and B3LYP/6-311G(df,p) levels of theory and by comparison with vibrational spectra of phenol, nitrobenzene, 2-nitrophenol and p-nitrophenol. The second nitro group brings a large atomic charge to the phenol ring, especially on C4 atom and this is mainly reflected in frequency sequence and intensity pattern of some ?(CC) vibrations with ?(NO 2) symmetric stretch contributions. The characteristic marker IR bands of DNP are discussed, and the intensities of several bands have been explained. It is also shown that in spite of its simplicity, AM1 semiempirical method is able to give surprisingly good agreement with experiment, especially for hydrogen bonding parameters in DNP.

Chi?, Vasile

2004-05-01

238

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

NASA Astrophysics Data System (ADS)

Full-dimensional multiconfiguration time-dependent Hartree (MCTDH) computations are reported for the vibrational states of the H5+ and its H4D+, H3D2+, H2D3+, HD4+, D5+ isotopologues employing two recent analytical potential energy surfaces of Xie et al. [J. Chem. Phys. 122, 224307 (2005)] and Aguado et al. [J. Chem. Phys. 133, 024306 (2010)]. The potential energy operators are constructed using the n-mode representation adapted to a four-combined mode cluster expansion, including up to seven-dimensional grids, chosen adequately to take advantage in representing the MCTDH wavefunction. An error analysis is performed to quantify the convergence of the potential expansion to reproduce the reference surfaces at the energies of interest. An extensive analysis of the vibrational ground state properties of these isotopes and comparison with the reference diffusion Monte Carlo results by Acioli et al. [J. Chem. Phys. 128, 104318 (2008)] are presented. It is found that these systems are highly delocalized, interconverting between equivalent minima through rotation and internal proton transfer motions even at their vibrational ground state. Isotopic substitution affects the zero-point energy and structure, showing preference in the arrangements of the H and D within the mixed clusters, and the most stable conformers of each isotopomer are the ones with the H in the central position. Vibrational excited states are also computed and by comparing the energies and structures predicted from the two surfaces, the effect of the potential topology on them is discussed.

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

2012-12-01

239

Calculating the Right-Eigenvectors of a Special Vibration Chain by Means of Modified Laguerre Polynomials  

NASA Astrophysics Data System (ADS)

This contribution deals with the identification of the right-eigenvectors of a linear vibration system with arbitrary n degrees of freedom as given in [1]. Applying the special distribution of stiffnesses and masses given in [1] yields a remarkable sequence of matrices for arbi- trary n. For computing the (right-)eigenvectors a generalised approach allowing the use of Laguerre polynomials is performed.

Weber, Wolfgang; Zastrau, Bernd W.; Anders, Bernd

2013-12-01

240

Vibrational properties of RbNd(WO4)2: high pressure Raman study, structural and phonon calculations.  

PubMed

RbNd(WO(4))(2) was investigated by high pressure Raman spectroscopy in the 0.1-12.3 GPa pressure interval. The assignment of modes was made based on lattice dynamics calculations and the results of these calculations helped us to also discuss the high pressure behavior of phonon spectra in this material. Our results show that a double oxygen bridge plays a fundamental role in the vibrational properties of this system. A density functional theory (DFT) calculation of hydrostatic pressure effects on RbNd(WO(4))(2) was performed in order to understand the effect of internal bond changes on the vibrational properties of RbNd(WO(4))(2). No pressure induced structural phase transition was observed in the Raman study at room temperature, and the DFT calculation (T = 0 K) is consistent with this result. The anomalous softening of the bridge stretching mode at 770 cm(-1) was attributed to the decrease of W-O1-W bond angle with increasing pressure. PMID:21937777

Paraguassu, W; Maczka, M; Guerini, S; Freire, P T C; Mendes Filho, J; Majchrowski, A; Swirkowicz, M

2011-10-12

241

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

242

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

243

Eigenmodes and eigenfrequencies of vibrating elliptic membranes: a Klein oscillation theorem and numerical calculations  

Microsoft Academic Search

We give a complete proof of the existence of eigenmodes for a vibrating elliptic membrane: for each pair (m;n) 2 f0; 1; 2;:::g2 there exists a unique even eigenmode with m ellipses and n hyperbola branches as nodal curves and, similarly, for each (m;n) 2 f0; 1; 2;:::g f 1; 2;:::g there exists a unique odd eigenmode with m ellipses

Armando G. M. Neves

2010-01-01

244

Vibration characteristics of composite piezoceramic plates at resonant frequencies: experiments and numerical calculations  

Microsoft Academic Search

The experimental measurement of the resonant frequencies for the piezoceramic material is generally performed by impedance analysis. In this paper, we employ an optical interferometry method called the amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) to investigate the vibration characteristics of piezoceramic\\/aluminum laminated plates. The AF-ESPI is a powerful tool for the full-field, noncontact, and real-time measurement method of surface displacement

Chi-Hung Huang; Chien-Ching Ma

2001-01-01

245

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

PubMed

Full-dimensional multiconfiguration time-dependent Hartree (MCTDH) computations are reported for the vibrational states of the H(5)(+) and its H(4)D(+), H(3)D(2)(+), H(2)D(3)(+), HD(4)(+), D(5)(+) isotopologues employing two recent analytical potential energy surfaces of Xie et al. [J. Chem. Phys. 122, 224307 (2005)] and Aguado et al. [J. Chem. Phys. 133, 024306 (2010)]. The potential energy operators are constructed using the n-mode representation adapted to a four-combined mode cluster expansion, including up to seven-dimensional grids, chosen adequately to take advantage in representing the MCTDH wavefunction. An error analysis is performed to quantify the convergence of the potential expansion to reproduce the reference surfaces at the energies of interest. An extensive analysis of the vibrational ground state properties of these isotopes and comparison with the reference diffusion Monte Carlo results by Acioli et al. [J. Chem. Phys. 128, 104318 (2008)] are presented. It is found that these systems are highly delocalized, interconverting between equivalent minima through rotation and internal proton transfer motions even at their vibrational ground state. Isotopic substitution affects the zero-point energy and structure, showing preference in the arrangements of the H and D within the mixed clusters, and the most stable conformers of each isotopomer are the ones with the H in the central position. Vibrational excited states are also computed and by comparing the energies and structures predicted from the two surfaces, the effect of the potential topology on them is discussed. PMID:23231232

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

2012-12-01

246

Use of a nondirect-product basis for treating singularities in triatomic rotational-vibrational calculations.  

PubMed

A technique has been developed which in principle allows the determination of the full rotational-vibrational eigenspectrum of triatomic molecules by treating the important singularities present in the triatomic rotational-vibrational kinetic energy operator given in Jacobi coordinates and the R(1) embedding. The singular term related to the diatom-type coordinate, R(1), deemed to be unimportant for spectroscopic applications, is given no special attention. The work extends a previous [J. Chem. Phys., 2005, 122, 024101] vibration-only approach and employs a generalized finite basis representation (GFBR) resulting in a nonsymmetric Hamiltonian matrix [J. Chem. Phys., 2006, 124, 014110]. The basis set to be used is obtained by taking the direct product of a 1-D DVR basis, related to R(1), with a 5-D nondirect-product basis, the latter formed by coupling Bessel-DVR functions depending on the distance-type coordinate causing the singularity, associated Legendre polynomials depending on the Jacobi angle, and rotational functions depending on the three Euler angles. The robust implicitly restarted Arnoldi method within the ARPACK package is used for the determination of a number of eigenvalues of the nonsymmetric Hamiltonian matrix. The suitability of the proposed approach is shown by the determination of the rotational-vibrational energy levels of the ground electronic state of H(3)(+) somewhat above its barrier to linearity. Convergence of the eigenenergies is checked by an alternative approach, employing a Hamiltonian expressed in Radau coordinates, a standard direct-product basis, and no treatment of the singularities. PMID:17664964

Czakó, Gábor; Furtenbacher, Tibor; Barletta, Paolo; Császár, Attila G; Szalay, Viktor; Sutcliffe, Brian T

2007-07-14

247

PARAMETER ANALYSIS FOR A HIGH-GAIN HARMONIC GENERATION FEL BY NUMERICAL CALCULATION BASED ON 1D THEORY  

Microsoft Academic Search

High-gain harmonic generation (HGHG) free-electron laser (FEL) is an important candidate for fourth- generation light source. Lots of research works about it have been done all along. Recently a further 1D theory about HGHG FEL has been developed. It considers the effects of different parameters for the whole process. An initial program based on this theory has been made. In

Li Yuhui; Jia Qika; Zhang Shancai

248

Conformational stability of cyclobutanol from temperature dependent infrared spectra of xenon solutions, r0 structural parameters, ab initio calculations and vibrational assignment  

NASA Astrophysics Data System (ADS)

Variable temperature (-55 to -100 °C) studies of the infrared spectra (4000-400 cm -1) of cyclobutanol, c-C 4H 7OH dissolved in liquid xenon have been carried out. The infrared spectrum (4000-100 cm -1) of the gas has also been recorded. From these data two of the four possible stable conformers have been confidently identified and their order of stabilities has been experimentally determined where the first indicator is for the position of attachment of the hydroxyl group on the bent cyclobutyl ring (Eq = equatorial or Ax = axial) and the second one ( t = trans, g = gauche) is the relative position of the hydroxyl rotor, i.e. rotation around the ring C sbnd O bond. The enthalpy difference between the most stable Eq- t conformer and the second most stable rotamer, Eq- g, has been determined to be 200 ± 50 cm -1 (2.39 ± 0.60 kJ/mol). This experimentally determined order is consistent with the order of stability predicted by ab initio calculations Eq- t > Eq- g > Ax- g > Ax- t. Evidence was obtained for the third conformer Ax- g which is predicted by ab initio calculations to be less stable by more than 650 cm -1 than the Eq- t form. The percentage of each conformer at ambient temperature is estimated to be Eq- t (50%), Eq- g (47%) and Ax- g (3%). The conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies have been obtained for all of the conformers from MP2(full)/6-31G(d) ab initio calculations. The optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing several different basis sets up to MP2(full)/aug-cc-pVTZ and from density functional theory calculations by the B3LYP method. By utilizing previously reported microwave rotational constants for the Eq- t conformer combined with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters have been obtained. The determined heavy atom structural parameters for the Eq- t conformer are: the distances C 1sbnd C 4 = 1.547(5) Å, C 4sbnd C 6 = 1.552(5) Å, C sbnd O = 1.416(5) Å and angles ?C 6C 4C 1 = 86.6(5)°, ?C 4C 1C 5 = 88.9(5)° and ?C 6C 5C 1C 4 = 22.8(5)°. The results are discussed and compared to the corresponding properties of some similar molecules.

Durig, James R.; Ganguly, Arindam; El Defrawy, Ahmed M.; Gounev, Todor K.; Guirgis, Gamil A.

2008-12-01

249

Infrared and NMR spectra, tautomerism, vibrational assignment, normal coordinate analysis, and quantum mechanical calculations of 4-amino-5-pyrimidinecarbonitrile  

NASA Astrophysics Data System (ADS)

The infrared (4000-200 cm-1) spectrum for 4-amino-5-pyrimidinecarbonitrile (APC, C5H4N4) was acquired in the solid phase. In addition, the 1H and 13C NMR spectra of APC were obtained in DMSO-d6 along with its mass spectrum. Initially, six isomers were hypothesized and then investigated by means of DFT/B3LYP and MP2(full) quantum mechanical calculations using a 6-31G(d) basis set. Moreover, the 1H and 13C NMR chemical shifts were predicted using a GIAO approximation at the 6-311+G(d,p) basis set and the B3LYP method with (and without) solvent effects using PCM method. The correlation coefficients showed good agreement between the experimental/theoretical chemical shift values of amino tautomers (1 and 2) rather than the eliminated imino tautomers (3-6), in agreement with the current quantum mechanical calculations. Structures 3-6 are less stable than the amino tautomers (1 and 2) by about 5206-8673 cm-1 (62.3-103.7 kJ/mol). The MP2(full)/6-31G(d) computational results favor the amino structure 1 with a pyramidal NH2 moiety and calculated real vibrational frequencies, however; structure 2 is considered a transition state owing to the calculated imaginary frequency. It is worth mentioning that, the calculated structural parameters suggest a strong conjugation between the amino nitrogen and pyrimidine ring. Aided by frequency calculations, normal coordinate analysis, force constants and potential energy distributions (PEDs), a complete vibrational assignment for the observed bands is proposed herein. Finally, NH2 internal rotation barriers for the stable non-planar isomer (1) were carried out using MP2(full)/6-31G(d) optimized structural parameters. Our results are discussed herein and compared to structural parameters for similar molecules whenever appropriate.

Afifi, Mahmoud S.; Farag, Rabei S.; Shaaban, Ibrahim A.; Wilson, Lee D.; Zoghaib, Wajdi M.; Mohamed, Tarek A.

250

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

PubMed

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, (1)H and (13)C 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. PMID:24892542

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

2014-11-11

251

The vibrational predissociation of cis-methyl nitrite in the S1 state: A comparison of exact quantum mechanical wave packet calculations with classical trajectory calculations and detailed experimental results  

Microsoft Academic Search

We present quantum mechanical wave packet calculations for the vibrational predissociation of cis-CH3ONO in the S1 state including three degrees of freedom—the CH3O–NO dissociation bond, the N=O stretching coordinate, and the CH3O–N–O bending angle. We calculate the autocorrelation function, the absorption spectrum, the lifetimes of the excited complex as a function of the internal excitation, and the final vibrational-rotational state

Agathe Untch; Reinhard Schinke; René Cotting; J. Robert Huber

1993-01-01

252

Calculation of the structure and vibrational states for anionic forms of Co-, Ni-, and Cu-porphines  

NASA Astrophysics Data System (ADS)

The structure and vibrations of neutral porphine metal complexes (Me-P, Me = Co, Ni, Cu) and their d-anionic forms with an additional electron localized in vacant d_x^2 -_y^2 - and d_z^2 -orbitals are compared based on calculations by a DFT method. It is shown that such electron population causes a significant increase of the electronic charge on the macrocycle rather than on the Me atom and is accompanied by a considerable redistribution of ?- and ?-electron densities (?? ??). A predominant gain of ?? (0.49e) is found for the monoanion of Co-P (Co-P-, d_z^2 -monoanion); of ?? (0.6e), for Ni-P-( d_x^2 -_y^2 - monoanion). These features are reflected in both the structure of the anions and the behavior of their vibrational frequencies. The greatest frequency shifts among IR active modes when populating the d_z^2 - and d_x^2 -_y^2 - orbitals occur for out-of-plane vibrations (>30 cm-1) and in-plane modes (34-46 cm-1) involving MeN- and C?Cm-bonds, respectively. Abnormally large frequency lowering is found for B1g-type modes (active in the resonance Raman spectrum) involving mainly C?Cm-, C?C?-, C?C?-, and MeN-bonds. This is related to a change in the d?-eg interaction strength during such vibrations that contributes to a decrease in the corresponding force constants.

Ivashin, N. V.

2010-03-01

253

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

254

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

NASA Astrophysics Data System (ADS)

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

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

1999-10-01

255

Structure and vibrational modes of AgI-doped AsSe glasses: Raman scattering and ab initio calculations  

SciTech Connect

We report an investigation of the structure and vibrational modes of (AgI){sub x} (AsSe){sub 100-x}, bulk glasses using Raman spectroscopy and first principles calculations. The short- and medium-range structural order of the glasses was elucidated by analyzing the reduced Raman spectra, recorded at off-resonance conditions. Three distinct local environments were revealed for the AsSe glass including stoichiometric-like and As-rich network sub-structures, and cage-like molecules (As{sub 4}Se{sub n}, n=3, 4) decoupled from the network. To facilitate the interpretation of the Raman spectra ab initio calculations are employed to study the geometric and vibrational properties of As{sub 4}Se{sub n} molecular units that are parts of the glass structure. The incorporation of AgI causes appreciable structural changes into the glass structure. AgI is responsible for the population reduction of molecular units and for the degradation of the As-rich network-like sub-structure via the introduction of As-I terminal bonds. Ab initio calculations of mixed chalcohalide pyramids AsSe{sub m}I{sub 3-m} provided useful information augmenting the interpretation of the Raman spectra. -- Graphical abstract: Raman scattering and ab initio calculations are employed to study the structure of AgI-AsSe superionic glasses. The role of mixed chalcohalide pyramidal units as illustrated in the figure is elucidated. Display Omitted Research highlights: {yields} Doping binary As-Se glasses with AgI cause dramatic changes in glass structure. {yields} Raman scattering and ab initio calculations determine changes in short- and medium-range order. {yields} Three local environments exist in AsSe glass including a network sub-structure and cage-like molecules. {yields} Mixed chalcohalide pyramids AsSe{sub m}I{sub 3-m} dominate the AgI-doped glass structure.

Kostadinova, O. [Foundation for Research and Technology Hellas, Institute of Chemical Engineering and High Temperature Chemical Processes, P.O. Box 1414, Patras GR-26504 (Greece); Chrissanthopoulos, A. [Foundation for Research and Technology Hellas, Institute of Chemical Engineering and High Temperature Chemical Processes, P.O. Box 1414, Patras GR-26504 (Greece); Department of Chemistry, University of Patras, Patras GR-26504 (Greece); Petkova, T. [Institute of Electrochemistry and Energy Systems (IEES), Bulgarian Academy of Sciences, Sofia (Bulgaria); Petkov, P. [Laboratory of Thin Film Technology, Department of Physics, University of Chemical Technology and Metallurgy, Sofia (Bulgaria); Yannopoulos, S.N., E-mail: sny@iceht.forth.g [Foundation for Research and Technology Hellas, Institute of Chemical Engineering and High Temperature Chemical Processes, P.O. Box 1414, Patras GR-26504 (Greece)

2011-02-15

256

The structure of n-alkanes: High precision abinitio calculation and relation to vibrational spectra  

Microsoft Academic Search

Detailed geometries and deuterium-isolated CH stretching frequencies are calculated for several different conformers of small n-alkanes at a number of levels of abinitio theory. The results of the calculations are carefully compared to experiment. The calculated frequencies fit a linear correlation to the calculated bond lengths with a mean absolute error of about 3 cm?1. The experimental frequencies fit this

A. L. Aljibury; R. G. Snyder; Herbert L. Strauss; Krishnan Raghavachari

1986-01-01

257

Higher harmonic control for rotary wing aircraft  

NASA Technical Reports Server (NTRS)

Higher Harmonic Control reduces helicopter airframe vibration through the exercise of rotor blade pitch control at frequencies that are higher harmonics of rotor rotation. Analysis wind tunnel tests and flight tests of this technology with an OH-6A helicopter have led to vibration reduction levels of the order of more than 80 percent. Blade feathering capability at rotor speed harmonics other than the first also promises the improvement of such rotor characteristics as acoustics, aerodynamic efficiency and ground resonance.

Gupta, B. P.; Logan, A. H.; Wood, E. R.

1984-01-01

258

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

NASA Technical Reports Server (NTRS)

The vibrational frequencies of MO2 are computed at many levels of theory, including HF, B3LYP, BP86, CASSCF, MP2, and CCSD(T). The computed results are compared with the available experimental results. Most of the methods fail for at least one state of the systems considered. The accuracy of the results and the origin of the observed failures are discussed. The B3LYP bond energies are compared with traditional methods for a variety of systems, ranging from FeCOn+ to SiCln and its positive ions. The cases where B3LYP differs from the traditional methods are discussed.

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

1997-01-01

259

Ab Initio Potential Energy Surfaces and the Calculation of Accurate Vibrational Frequencies  

NASA Technical Reports Server (NTRS)

Due to advances in quantum mechanical methods over the last few years, it is now possible to determine ab initio potential energy surfaces in which fundamental vibrational frequencies are accurate to within plus or minus 8 cm(exp -1) on average, and molecular bond distances are accurate to within plus or minus 0.001-0.003 Angstroms, depending on the nature of the bond. That is, the potential energy surfaces have not been scaled or empirically adjusted in any way, showing that theoretical methods have progressed to the point of being useful in analyzing spectra that are not from a tightly controlled laboratory environment, such as vibrational spectra from the interstellar medium. Some recent examples demonstrating this accuracy will be presented and discussed. These include the HNO, CH4, C2H4, and ClCN molecules. The HNO molecule is interesting due to the very large H-N anharmonicity, while ClCN has a very large Fermi resonance. The ab initio studies for the CH4 and C2H4 molecules present the first accurate full quartic force fields of any kind (i.e., whether theoretical or empirical) for a five-atom and six-atom system, respectively.

Lee, Timothy J.; Dateo, Christopher E.; Martin, Jan M. L.; Taylor, Peter R.; Langhoff, Stephen R. (Technical Monitor)

1995-01-01

260

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

NASA Astrophysics Data System (ADS)

Voids at the tunnel-soil interface are not normally considered when predicting ground vibration from underground railways. The soil is generally assumed to be continuously bonded to the outer surface of the tunnel to simplify the modelling process. Evidence of voids around underground railways motivated the study presented herein to quantify the level of uncertainty in ground vibration predictions associated with neglecting to include such voids at the tunnel-soil interface. A semi-analytical method is developed which derives discrete transfers for the coupled tunnel-soil model based on the continuous Pipe-in-Pipe method. The void is simulated by uncoupling the appropriate nodes at the interface to prevent force transfer between the systems. The results from this investigation show that relatively small voids ( 4 m×90?) can significantly affect the rms velocity predictions in the near-field and moderately affect predictions in the far-field. Sensitivity of the predictions to void length and void sector angle are both deemed to be significant. The findings from this study suggest that the uncertainty associated with assuming a perfect bond at the tunnel-soil interface in an area with known voidage can reasonably reach ±5 dB and thus should be considered in the design process.

Jones, Simon; Hunt, Hugh

2011-01-01

261

Vibrational dynamics of single-crystal YVO4 studied by polarized micro-Raman spectroscopy and ab initio calculations  

NASA Astrophysics Data System (ADS)

The vibrational properties of yttrium orthovanadate (YVO4) single crystals, with tetragonal zircon structure, have been investigated by means of polarized micro-Raman spectroscopy and ab initio calculations. Raman spectra were taken at different polarizations and orientations carefully set by the use of a micromanipulator, so that all of the twelve Raman-active modes, expected on the basis of the group theory, were selected in turn and definitively assigned in wave number and symmetry. In particular the Eg(4) mode, assigned incorrectly in previous literature, has been observed at 387 cm-1. Moreover, the very weak Eg(1) mode, peaked at about 137 cm-1, was clearly observed only under some excitation wavelengths, and its peculiar Raman excitation profile was measured within a wide region of the visible. Finally, ab initio calculations based on density-functional theory have been performed in order to determine both Raman and infrared vibrational modes and to corroborate the experimental results. The rather good agreement between computational and experimental frequencies is slightly better than in previous computational works and supports our experimental symmetry assignments.

Sanson, Andrea; Giarola, Marco; Rossi, Barbara; Mariotto, Gino; Cazzanelli, Enzo; Speghini, Adolfo

2012-12-01

262

Molecular structure, anharmonic vibrational frequencies and NBO analysis of naphthalene acetic acid by density functional theory calculations  

NASA Astrophysics Data System (ADS)

In this work, we report anharmonic vibrational frequencies, molecular structure, NBO and HOMO, LUMO analysis of naphthalene acetic acid (NAA). The optimized geometric bond lengths and bond angles obtained by computation show good agreement with experimental X-ray data. The computed dimer parameters also show good agreement with experimental data. Anharmonic frequencies of NAA were determined and analyzed by DFT level of theory utilizing 6-311+G(d,p) basis set. Good agreement between the calculated and experimental spectra was obtained. Stability of the molecule arising from hyperconjugative interactions and charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in the ?* and ?* antibonding orbitals and E2 energies. This confirms the occurrence of ICT (Intermolecular Charge Transfer) within the molecule. The calculated HOMO and LUMO energies also show that charge transfer occurs within the molecule.

Kavitha, E.; Sundaraganesan, N.; Sebastian, S.; Kurt, M.

2010-10-01

263

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

264

Conformational analysis and vibrational study of daidzein by using FT-IR and FT-Raman spectroscopies and DFT calculations.  

PubMed

Daidzein (C15H10O4) is a type of isoflavone. It was isolated from Butea monosperma that belongs to the Fabaceae family. Soybeans and soy products are the abundant source of daidzein. It is the subject of investigation for many reasons, as it has got wide applications, such as anti-tumor, anti-estrogen, weak pro-estrogen and anti-cancer activities. In the present study, a complete vibrational assignment is provided for the observed IR and Raman spectra of daidzein. Electronic properties have been analyzed using TD-DFT method for both gaseous and solvent phase. The optimized geometry, total energy, potential energy surface and vibrational wavenumbers of daidzein have been determined using density functional theory (DFT/B3LYP) method with 6-311++G(d,p) basis set and a good correlation was found between observed and calculated values. The double well potential energy curve of the molecule about three bonds, has been plotted, as obtained from DFT/6-31G basis. The HOMO-LUMO energy gap of possible conformers has been calculated for comparing their chemical activity. Global reactivity descriptors have been calculated for predicting the chemical reactivity and the stability of chemical systems. Electrostatic potential surface has been plotted for predicting the structure activity relationship. NBO analysis has also been performed to study the stability of the molecule. NLO study reveals the nonlinear properties of the molecule. 1H and 13C NMR spectra have also been studied. Finally, the calculated results were used to simulate infrared and Raman spectra of the title compound which showed a good agreement with the observed spectra. PMID:24211623

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

2014-02-24

265

Scaling factors for fundamental vibrational frequencies and zero-point energies obtained from HF, MP2, and DFT\\/DZP and TZP harmonic frequencies  

Microsoft Academic Search

Recently, segmented contracted basis sets of double, triple, and quadruple zeta valence quality plus polarization functions (XZP, X=D, T, and Q) for the atoms from H to Ar were presented by Jorge et al. Scaling factors for the fundamental vibrational frequencies, low-frequency vibrations, and zero-point vibrational energies (ZPVEs) evaluated at 14 levels of theory are reported. The ab initio Hartree–Fock

S. G. Andrade; Luísa C. S. Gonçalves; F. E. Jorge

2008-01-01

266

Calculation of vibrational HDO energy levels: Analysis of perturbation theory series  

NASA Astrophysics Data System (ADS)

Series of the Rayleigh-Schrödinger perturbation theory are analyzed and summated by the example of the HD16O molecule for vibrational energy levels. Particular attention is given to determining the location of singularities-branching points corresponding to the intersection of levels in the complex plane. Numerical analysis demonstrates the divergence of the series for states involved in the Fermi resonance; however, summation by the method of Padé-Hermite approximants makes it possible to reconstruct the levels by coefficients of the series with sufficient accuracy. It is found that resonance-coupled states have common branching points, which leads to the coincidence of series' coefficients in high orders. Branching points' characteristics permitting one to obtain a comparatively simple representation of high order corrections are determined.

Bykov, A. D.; Kalinin, K. V.; Duchko, A. N.

2013-03-01

267

Vibrational properties of hexagonal boron nitride: inelastic X-ray scattering and ab initio calculations.  

PubMed

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. PMID:17359168

Serrano, J; Bosak, A; Arenal, R; Krisch, M; Watanabe, K; Taniguchi, T; Kanda, H; Rubio, A; Wirtz, L

2007-03-01

268

Pushing the limits in accurate vibrational structure calculations: anharmonic frequencies of lithium fluoride clusters (LiF)n, n = 2-10.  

PubMed

The vibrational spectra of a series of small lithium fluoride clusters, i.e. (LiF)n, n = 2-10, were studied by vibrational configuration interaction (VCI) calculations relying on potential energy surfaces including three-mode coupling terms and being obtained from explicitly correlated local coupled cluster calculations. Due to the account for anharmonicity effects, the simulated spectra allow for a direct comparison with experimental data and may thus help to identify clusters in the experiments. Even structurally closely related clusters can clearly be distinguished by infrared spectroscopy. The largest system in this study required more than 1000 basis functions in the electronic structure calculations and more than 10(7) configurations in the vibrational structure calculations and became computationally feasible only due to a combination of different approximations and highly parallelized algorithms. PMID:24981078

Oschetzki, Dominik; Rauhut, Guntram

2014-07-16

269

Image resolution limits resulting from mechanical vibrations. Part IV: real-time numerical calculation of optical transfer functions and experimental verification  

Microsoft Academic Search

A method of calculating numerically the optical transfer function appropriate to any type of image motion and vibration, including random ones, has been developed. We compare the numerical calculation method to the experimental measurement; the close agreement justifies implementation in image restoration for blurring from any type of image motion. In addition, statistics regarding the limitation of resolution as a

Ofer Hadar; Itai Dror; Norman S. Kopeika

1994-01-01

270

Contribution to harmonic balance calculations of self-sustained periodic oscillations with focus on single-reed instruments.  

PubMed

The harmonic balance method (HBM) was originally developed for finding periodic solutions of electronical and mechanical systems under a periodic force, but has been adapted to self-sustained musical instruments. Unlike time-domain methods, this frequency-domain method does not capture transients and so is not adapted for sound synthesis. However, its independence of time makes it very useful for studying any periodic solution, whether stable or unstable, without care of particular initial conditions in time. A computer program for solving general problems involving nonlinearly coupled exciter and resonator, HARMBAL, has been developed based on the HBM. The method as well as convergence improvements and continuation facilities are thoroughly presented and discussed in the present paper. Applications of the method are demonstrated, especially on problems with severe difficulties of convergence: the Helmholtz motion (square signals) of single-reed instruments when no losses are taken into account, the reed being modeled as a simple spring. PMID:16583920

Farner, Snorre; Vergez, Christophe; Kergomard, Jean; Lizée, Aude

2006-03-01

271

Charge transfer in systems of conjugated bonds in cyanobiphenyl molecules: Quantum-chemical calculations of the structure and vibrational spectra  

NASA Astrophysics Data System (ADS)

Quantum-chemical calculations of the IR absorption spectra and geometric and electronic structure of cyanobiphenyl molecules [Figure not available: see fulltext.] (I) were performed for various angles between benzene ring planes by the B3LYP/6-31+G** method. It was shown that the stablest conformation of I (X=OCH3, OC3H7) should be the twist conformation with ?= 37°, which was in agreement with the gas-phase experimental data. Rotation of benzene rings with respect to each other changed the relative orientation of the interacting ? orbitals of the bridge ring carbon atoms and caused charge redistribution over molecule atoms, in particular, over terminal X and CN group atoms. The calculated period of charge oscillations on the alkyl and nitro groups coincided with the period of reversible charge transfer (˜5-10 fs) between the conjugated subsystems (benzene ring + substituent) observed as the ? angle changed. The rate of charge transfer between the electron donor and electron acceptor groups was calculated to be (3-6)×105 m/s. Charge oscillations on benzene ring carbon atoms and donor and acceptor groups did not cause similar dipole moment oscillations and vibrations in the IR spectrum. The dipole moment of the molecule decreases as the angle between benzene ring planes increases, and the passage to the “perpendicular” conformation should increase the C?N stretching vibration frequency by ˜5 cm-1 and decrease the intensity of the IR band by ˜2 times. The elongation of the aliphatic chain in the X group did not cause noticeable changes in the geometric and electronic structure of the molecule.

Isaev, A. N.; Shorygin, P. P.

2009-03-01

272

Infrared and Raman spectra, conformational stability, ab initio calculations of structure, and vibrational assignment of 2-hexyne  

NASA Astrophysics Data System (ADS)

The infrared spectra (3500-50 cm -1) of the gas and solid and the Raman spectra (3500-50 cm -1) of the liquid and solid have been recorded for 2-hexyne, CH 3-C?C-CH 2CH 2CH 3. Variable temperature studies of the infrared spectrum (3500-400 cm -1) of 2-hexyne dissolved in liquid krypton have also been recorded. Utilizing four anti/ gauche conformer pairs, the anti( trans) conformer is found to be the lower energy form with an enthalpy difference of 74±8 cm -1 (0.88±0.10 kJ/mol) determined from krypton solutions over the temperature range -105 to -150 °C. At room temperature it is estimated that there is 42% of the anti conformer present. Equilibrium geometries and energies of the two conformers have been determined by ab initio (HF and MP2) and hybrid DFT (B3LYP) methods using a number of basis sets. Only the HF and DFT methods predict the anti conformer as the more stable form as found experimentally. A vibrational assignment is proposed based on the force constants, relative intensities, depolarization ratios from the ab initio and DFT calculations and on rotational band contours obtained using the calculated equilibrium geometries. From calculated energies it is shown that the CH 3 group exhibits almost completely free rotation which is in agreement with the observation of sub-band structure for the degenerate methyl vibrations from which values of the Coriolis coupling constants, ?, have been determined. The results are compared to similar properties of some corresponding molecules.

Bell, Stephen; Zhu, Xiaodong; Guirgis, Gamil A.; Durig, James R.

2002-10-01

273

Composed vibration pulses for ultrasound vibrometry  

Microsoft Academic Search

Composed vibration pulses are developed to generate ultrasound radiation force for stimulating vibrations in a tissue region with preferred spectral distributions and increasing specific vibration harmonics when the peak radiation power is limited. The new vibration sequence has multiple pulses in one fundamental period of the vibration. The pulses are sparsely sampled from an orthogonal frequency wave composed of several

Yi Zheng; Aiping Yao; Yu Liu; Ke Chen; Shigao Chen; Matthew W. Urban; James F. Greenleaf

2010-01-01

274

Ab initio calculations of the elastic, electronic, optical, and vibrational properties of PdGa compound under pressure  

NASA Astrophysics Data System (ADS)

The structural, elastic, electronic, optical, and vibrational properties of cubic PdGa compound are investigated using the norm-conserving pseudopotentials within the local density approximation (LDA) in the framework of the density functional theory. The calculated lattice constant has been compared with the experimental value and has been found to be in good agreement with experimental data. The obtained electronic band structures show that PdGa compound has no band gap. The second-order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, and Debye temperature have also been estimated. Our calculated results of elastic constants show that this compound is mechanically stable. Furthermore, the real and imaginary parts of the dielectric function and the optical constants such as the electron energy-loss function, the optical dielectric constant and the effective number of electrons per unit cell are calculated and presented in the study. The phonon dispersion curves are also derived using the direct method.

Koc, H.; Yildirim, A.; Deligoz, E.

2012-09-01

275

Raman and infrared spectra, conformational stability, normal coordinate analysis, vibrational assignment, and ab initio calculations of trans-3-pentenenitrile  

NASA Astrophysics Data System (ADS)

The Raman (3200-20 cm -1) spectra of liquid and solid trans-CH 3CH?CHCH 2CN, and the infrared (3200-30 cm -1) spectra of gaseous and solid trans-3-pentenenitrile have been recorded. The spectra of the fluid phases are consistent with two stable conformers in equilibrium at ambient temperature. The mid-infrared spectra of the sample dissolved in liquid xenon as a function of temperature (-100 to -55°C) have been recorded. Utilizing two conformer pairs, the enthalpy difference has been determined to be 205±7 cm-1(2.45±0.08 kJ/mol) with the syn conformer being the more stable form. Vibrational assignments for the 33 normal modes for the syn conformer and several of those for the gauche form are proposed. The structural parameters, dipole moments, conformational stability, and vibrational frequencies have been determined from ab initio calculations. The predicted conformational stability is consistent with the experimental results. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.

Durig, J. R.; Gounev, T. K.; Zhen, H.; Drew, A.; Shen, S.; Guirgis, G. A.

2000-10-01

276

Vibrational spectroscopic study of fluticasone propionate  

NASA Astrophysics Data System (ADS)

Fluticasone propionate is a synthetic glucocorticoid with potent anti-inflammatory activity that has been used effectively in the treatment of chronic asthma. The present work reports a vibrational spectroscopic study of fluticasone propionate and gives proposed molecular assignments on the basis of ab initio calculations using BLYP density functional theory with a 6-31G* basis set and vibrational frequencies predicted within the quasi-harmonic approximation. Several spectral features and band intensities are explained. This study generated a library of information that can be employed to aid the process monitoring of fluticasone propionate.

Ali, H. R. H.; Edwards, H. G. M.; Kendrick, J.; Scowen, I. J.

2009-03-01

277

Analysis of methods for calculating the transition frequencies of the torsional vibration of acrolein isomers in the ground ( S 0) electronic state  

NASA Astrophysics Data System (ADS)

B3LYP, MP2, CCSD(T), and MP4/MP2 in the 6-311G( d, p), 6-311++G( d, p), cc-pVTZ, aug-cc-pVTZ bases used to calculate the transition frequencies of torsional vibration of trans- and cis-isomers of acrolein in the ground electronic state ( S 0) are analyzed. It is found that for trans-isomers, all methods of calculation except for B3LYP in the cc-pVTZ basis yield good agreement between the calculated and experimental values. It is noted that for the cis-isomer of acrolein, no method of calculation confirms the experimental value of the frequency of torsional vibration (138 cm-1). It is shown that the calculated and experimental values for obertones at 273.0 cm-1 and other transitions of torsional vibration are different for this isomer in particular. However, it is established that in some calculation methods (B3LYP, MP2), the frequency of the torsional vibration of the cis-isomer coincides with another experimental value of this frequency (166.5 cm-1). It is concluded that in analyzing the vibrational structure of the UV spectrum, the calculated and experimental values of its obertone (331.3 cm-1) coincide, along with its frequency. It is also noted that the frequency of torsional vibration for the cis-isomer (166.5 cm-1) can also be found in other experimental works if we change the allocation of torsional transition 18{1/1}.

Koroleva, L. A.; Tyulin, V. I.; Matveev, V. K.; Pentin, Yu. A.

2013-05-01

278

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

279

Torque and efficiency calculation of an interior permanent magnet motor considering harmonic iron losses of both the stator and rotor  

Microsoft Academic Search

A method to estimate characteristics of interior permanent magnet motors considering effects of iron loss is introduced. The equivalent circuit parameters including the iron loss resistance are calculated as functions of d-q axis currents by the finite-element method with the consideration of movement of the rotor. The characteristics of the motor are calculated from the equivalent circuit. By using this

Katsumi Yamazaki

2003-01-01

280

A method to improve the agreement between calculated and observed vibrational frequencies after scaling of a quantum mechanical force field  

NASA Astrophysics Data System (ADS)

A systematic method to fit calculated to observed vibrational frequencies has been developed and implemented in a computer program. The procedure consists of the refinement of a scaled quantum mechanical force field (SQMFF) previously obtained according to Pulay's method. The key step in the process is the generation of an intermediate matrix, C?CT, which is then refined. The above step produces only small corrections to the scaled force constants, yielding a considerable improvement of the fitted frequencies. This scheme of refinement can be carried out using any kind of coordinates. To show the reliability and performance of the proposed method, the force fields of two very different systems, as benzene and tetranitromethane, have been chosen as example tests.

Arenas, Juan F.; Centeno, Silvia P.; Marcos, Juan I.; Otero, Juan C.; Soto, Juan

2000-11-01

281

Vibrational spectroscopic studies (FT-IR, FT-Raman, SERS) and quantum chemical calculations on cyclobenzaprinium salicylate.  

PubMed

FT-IR, FT-Raman and surface enhanced Raman scattering spectra of cyclobenzaprinium salicylate were recorded and analyzed. The vibrational wavenumbers were examined theoretically using the Gaussian09 set of quantum chemistry codes, and the normal modes were assigned by potential energy distribution calculations. The downshift of the OH stretching frequency is due to strong hydrogen bonded system present in the title compound as given by XRD results. The presence of CH3, CH2 and CO2 modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface which affects the orientation and metal molecule interaction. The presence of phenyl ring modes in the SERS spectrum indicates a tilted orientation with respect to the metal surface. The geometrical parameters of the title compound are in agreement with XRD results. A computation of the first hyperpolarizability indicates that the compound may be a good candidate as a NLO material. PMID:24200648

Mary, Y Shyma; Jojo, P J; Van Alsenoy, Christian; Kaur, Manpreet; Siddegowda, M S; Yathirajan, H S; Nogueira, Helena I S; Cruz, Sandra M A

2014-02-24

282

IOS and ECS line coupling calculation for the CO-He system - Influence on the vibration-rotation band shapes  

NASA Technical Reports Server (NTRS)

Line coupling coefficients resulting from rotational excitation of CO perturbed by He are computed within the infinite order sudden approximation (IOSA) and within the energy corrected sudden approximation (ECSA). The influence of this line coupling on the 1-0 CO-He vibration-rotation band shape is then computed for the case of weakly overlapping lines in the 292-78 K temperature range. The IOS and ECS results differ only at 78 K by a weak amount at high frequencies. Comparison with an additive superposition of Lorentzian lines shows strong modifications in the troughs between the lines. These calculated modifications are in excellent quantitative agreement with recent experimental data for all the temperatures considered. The applicability of previous approaches to CO-He system, based on either the strong collision model or exponential energy gap law, is also discussed.

Boissoles, J.; Boulet, C.; Robert, D.; Green, S.

1987-01-01

283

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

NASA Astrophysics Data System (ADS)

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(x14 + x24) - b(x12 + x22) + cx12x22, where x1 and x2 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; Meinander, Niklas; Laane, Jaan

2014-04-01

284

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

PubMed

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(x1 (4) + x2 (4)) - b(x1 (2) + x2 (2)) + cx1 (2)x2 (2), where x1 and x2 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. PMID:24784278

Ocola, Esther J; Medders, Cross; Meinander, Niklas; Laane, Jaan

2014-04-28

285

Vibrational spectroscopic study and structure calculation for model compounds and polyurethanes  

SciTech Connect

Vibrational spectroscopy has been applied to the study of a small ring molecule, three model urethane compounds and Poly[4,4[prime]-bis(6-hydroxyhexyloxy)biphenyl-co-2,4-toluenediisocyanate] (2,4-TDI polyurethane) systems. The computer program POLYGRAF was used to estimate the stability of some conformers of the three model compounds. Grazing angle microscopy was used to study the surface structure of thin films of polyurethane. The synthesis, far infrared spectra, temperature dependent mid-infrared spectra and the Fourier transform Raman spectra are reported for polycrystalline samples of three model urethanes, 1,3-phenyl di(methyl carbamate) (1,3-PDI based urethane), 2,6-toluene di(methyl carbamate) (2,6-TDI based urethane), and 2,4-toluene di(methyl carbamate) (2,4-TDI based urethane). Geometry optimization is reported for phenyl methyl carbamate by ab initio and molecular mechanics methods, and of the three model urethanes by molecular mechanics methods using the Dreiding I force field. The results suggest that in isotropic surroundings only a very small number of the many possible conformers of the urethane groups in these molecules contribute appreciably to the structure. The intermolecular interaction, morphology and microstructure of 2,4-TDI polyurethane are studied. A molecular interpretation of hydrogen bonding behavior is given. The temperature dependence of infrared spectra of the 2,4-TDI polyurethane films are reported together with some kinetic data. A very thin film was prepared to study the surface behavior of 2,4-TDI polyurethane. An infrared spectrum was obtained by grazing angle reflection-absorption. The results suggest that 2,4-TDI polyurethane has a layered structure and that most of the NH groups and carbonyl groups are free on the surface. The infrared spectra of 1,4-cyclohexadiene and 1,4-cyclohexadiene-3,3,6,6-d4 were recorded in the gas phase at room temperature.

Wang, Q.

1992-01-01

286

Calculation of Rotor's Torsional Vibration Characteristics Based on Equivalent Diameter of Stiffness  

Microsoft Academic Search

In this paper, ANSYS finite element analysis software is used to simulate the twisted state of turbine integral rotor's discs. For various stepped shaft structure, the formula of ¿-stiffness influence coefficient is fit by changing the geometric parameters of the equal-thickness disc, then equivalent diameter of stiffness is obtained. For the cone-shaped disc, the equivalent diameter of stiffness is calculated

Wang-fan Li; Dan-mei Xie; Yong Qian; Xian-bo Zhao; Sun Cai; You-min Hou

2010-01-01

287

Identification of hydrogen defects in SrTiO3 by first principles local vibrational mode calculations  

SciTech Connect

For over three decades, the infrared spectroscopy peaks of around 3500 cm{sup -1} observed in hydrogen-doped SrTiO{sub 3} samples have been assigned to an interstitial hydrogen (H{sub i}) attached to a lattice oxygen with two possible configuration models: the octahedral edge (OE) and the cubic face (CF) models. Based on our first-principles calculations of H{sub i} around O, both OE and CF configurations are not energetically stable. Starting from either configuration, the H{sub i} would spontaneously relax into an off axis (OA) site; lowering the energy by 0.25 eV or more. The calculated vibrational frequency of 2745 cm{sup -1} for OA invalidates the assignment of H{sub i} to the observed 3500 cm{sup -1} peak. In addition, the calculated diffusion barrier is low, suggesting that H{sub i} can be easily annealed out. We propose that the observed peaks around 3500 cm{sup -1} are associated with defect complexes. A Sr vacancy (V{sub Sr}) can trap H{sub i} and form a H-V{sub Sr} complex which is both stable and has the frequency in agreement with the observed main peak. The complex can also trap another H{sub i} and form 2H-V{sub Sr}; consistent with the observed additional peaks at slightly higher frequencies (3510-3530 cm{sup -1}).

T-Thienprasert, J [Kasetsart University, Thailand; Fongkaew, Ittipon [Suranaree University; Singh, David J [ORNL; Du, Mao-Hua [ORNL; Limpijumnong, Sukit [Kasetsart University, Thailand

2012-01-01

288

Sum-frequency-generation vibration spectroscopy and density functional theory calculations with dispersion corrections (DFT-D2) for cellulose I? and I?.  

PubMed

Sum-frequency-generation (SFG) vibration spectroscopy selectively detects noncentrosymmetric vibrational modes in crystalline cellulose inside intact lignocellulose. However, SFG peak assignment in biomass samples is challenging due to the complexity of the SFG processes and the lack of reference SFG spectra from the two crystal forms synthesized in nature, cellulose I? and I?. This paper compares SFG spectra of laterally aligned cellulose I? and I? crystals with vibration frequencies calculated from density functional theory with dispersion corrections (DFT-D2). Two possible hydrogen-bond networks A and B ( Nishiyama et al. Biomacromolecules 2008 , 9 , 3133 ) were investigated for both polymorphs. From DFT-D2 calculations the energetically favorable structures for cellulose I? and I? had CH2OH groups in tg conformations and network A hydrogen bonding. The calculated frequencies of C-H stretch modes agreed reasonably well with the peak positions observed with SFG and were localized vibrations; thus, peak assignments to specific alkyl groups were proposed. DFT-D2 calculations underestimated the distances between hydrogen-bonded oxygen atoms compared to the experimentally determined values; therefore, the OH stretching calculated frequencies were ~100 cm(-1) lower than observed. The SFG peak assignments through comparison with DFT-D2 calculations will guide the SFG analysis of the crystalline cellulose structure in plant cell walls and lignocellulose biomass. PMID:23738844

Lee, Christopher M; Mohamed, Naseer M A; Watts, Heath D; Kubicki, James D; Kim, Seong H

2013-06-01

289

Brueckner-Hartree-Fock Calculations of Spherical Nuclei in a Harmonic-Oscillator Basis. III. Renormalized Calculations Using the Reid Potential  

Microsoft Academic Search

A G matrix derived from the Reid soft-core potential is used in a series of Brueckner-Hartree-Fock calculations of spherical nuclei. The G matrix is calculated using an intermediate-state spectrum and Pauli operator appropriate to pure oscillator orbitals, with options to shift the entire spectrum or the low-lying levels from unperturbed oscillator energies. The Pauli operator takes into account the filling

K. T. Davies; R. J. McCarthy

1971-01-01

290

Harmonic Drive.  

National Technical Information Service (NTIS)

The harmonic drive has utility in optical tracking telescopes, radar antenna drives, aircraft control surface actuators, and high precision X-Y plotting equipment. Two harmonic drive units, each having its own input motor, are coupled together. One of the...

R. H. Lapp

1965-01-01

291

Six-dimensional calculation of the vibrational spectrum of the HFCO molecule  

NASA Astrophysics Data System (ADS)

Bound energy levels, up to 5000 cm-1 of internal excitation, have been computed for the HFCO molecule. An exact six-dimensional (6D) quantum Hamiltonian, expressed in terms of Jacobi vectors, has been used. It is shown to lead to a compact form of the kinetic energy operator, easy to implement in the calculations. The primary discrete variable representation (DVR) basis set has been contracted by means of the adiabatic pseudospectral method of Friesner et al. [J. Chem. Phys. 99, 324 (1993)]. Two different, global, potential energy surfaces have been considered. The calculated energy levels have been successfully assigned by an automatic labeling procedure. These levels have been compared to the experimental results, providing a test of the accuracy of the existing surfaces.

Viel, Alexandra; Leforestier, Claude

2000-01-01

292

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

293

Conformational stability, r 0 structural parameters, ab initio calculations, and vibrational assignment for silacyclopentane  

Microsoft Academic Search

The infrared spectra (3500–50cm?1) of the gas and solid and the Raman spectrum (3200–30cm?1) of liquid silacyclopentane, c-C4H8SiH2, have been recorded. Additionally the infrared spectrum (3200–400cm?1) of liquid xenon solutions has been recorded at ?65 and ?95°C. In all of the physical states only one conformer was detected which is the twisted C2 form. The conformational energetics have been calculated

Gamil A. Guirgis; Ahmed M. El Defrawy; Todor K. Gounev; Mamdouh S. Soliman; James R. Durig

2007-01-01

294

Vibrational spectrum of the spin crossover complex [Fe(phen)(2)(NCS)(2)] studied by IR and Raman spectroscopy, nuclear inelastic scattering and DFT calculations.  

PubMed

The vibrational modes of the low-spin and high-spin isomers of the spin crossover complex [Fe(phen)(2)(NCS)(2)] (phen = 1,10-phenanthroline) have been measured by IR and Raman spectroscopy and by nuclear inelastic scattering. The vibrational frequencies and normal modes and the IR and Raman intensities have been calculated by density functional methods. The vibrational entropy difference between the two isomers, DeltaS(vib), which is--together with the electronic entropy difference DeltaS(el)--the driving force for the spin-transition, has been determined from the measured and from the calculated frequencies. The calculated difference (DeltaS(vib) = 57-70 J mol(-1) K(-1), depending on the method) is in qualitative agreement with experimental values (20-36 J mol(-1) K(-1)). Only the low energy vibrational modes (20% of the 147 modes of the free molecule) contribute to the entropy difference and about three quarters of the vibrational entropy difference are due to the 15 modes of the central FeN(6) octahedron. PMID:17047767

Ronayne, Kate L; Paulsen, Hauke; Höfer, Andreas; Dennis, Andrew C; Wolny, Juliusz A; Chumakov, Aleksandr I; Schünemann, Volker; Winkler, Heiner; Spiering, Hartmut; Bousseksou, Azzedine; Gütlich, Philipp; Trautwein, Alfred X; McGarvey, John J

2006-10-28

295

Experimental and theoretical study of the vibrational spectra of halothane  

Microsoft Academic Search

MP2 and B3LYP calculations carried out with the 6-311++G(df,pd) basis set show that the staggered structure of halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) is more stable than the eclipsed one. Results of natural bond orbital calculations for both structures are discussed. The experimental IR and Raman spectra of halothane pure and dissolved in carbon tetrachloride are investigated. The harmonic vibrational frequencies, and IR and

B. Czarnik-Matusewicz; D. Michalska; C. Sandorfy; Th. Zeegers-Huyskens

2006-01-01

296

Hybrid BEM\\/FEM Calculation of Thermal Rise in the Human Eye Exposed to Time Harmonic EM Waves  

Microsoft Academic Search

Human eye being unprotected by the layer of skin and bones is one of the most sensitive organs to EM radiation. The absorption of EM radiation is quantified in terms of SAR and to calculate the SAR the knowledge of complete electric field distribution inside the eye is necessary. In this paper the problem of distribution of near EM field

Hrvoje Dodig

2005-01-01

297

Ab Initio calculations and vibrational energy level fits for the lower singlet potential-energy surfaces of C3  

NASA Astrophysics Data System (ADS)

Ab initio multireference configuration interaction potential energy surfaces are computed for the eight lowest singlet surfaces of C3. These reveal several important features, including several conical intersections in linear, nonlinear, and equilateral triangle geometries. These intersections are important because, particularly for the excited A~ 1?u state, reasonable ab initio results could only be obtained by including nearby, near degenerate, 1?u- and 1?u states that cross the A~ 1?u state around 4500 cm-1 above the equilibrium geometry, and a 1?g state whose potential in turn crosses the other states about 2000 cm-1 further up. These states are probably responsible for the complexity of the shorter wavelength UV absorption spectrum of C3. The computed potential energy surface for the ground, X~ 1?g+, state and for the lowest two excited singlet surfaces (which both correlate with the A~ 1?u state in a collinear geometry) are fitted to analytic functional forms. Vibrational energy levels are calculated for both states, taking account of the Renner-Teller coupling in the excited A~ 1?u state. The potential parameters for both states are then least-squares fitted to experimental data. The ground-state fit covers a range of ~8500 cm-1 above the lowest level, and reproduces 100 observed vibrational levels with an average error of 2.8 cm-1. The A~ 1?u state surfaces cover a range of 3250 cm-1 above the zero-point level, and reproduce the 44 observed levels in this range with an average error of 2.8 cm-1.

Ahmed, Khalil; Balint-Kurti, Gabriel G.; Western, Colin M.

2004-11-01

298

Vibrational modes in epitaxial Ti1-xScxN(001) layers: An ab initio calculation and Raman spectroscopy study  

NASA Astrophysics Data System (ADS)

Ti1-xScxN alloys were used to investigate the effects of carrier density and the density of states (DOS) at the Fermi level Ef on vibrational modes, phonon anomalies, and superconducting transition temperatures Tc. Single-crystal Ti1-xScxN layers, 2000 Å thick, with compositions spanning the entire alloy range (0<=x<=1), were grown on MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition at 750 °C. The Raman spectrum of pure TiN is dominated by two-phonon features while Ti1-xScxN spectra with 0.12<=x<=0.81 exhibit primarily one-phonon peaks. The acoustic peak softens from 310 cm-1 with x=0.12 to ~=200 cm-1 with x=0.81, due to the corresponding increase in the lattice constant. All alloy layers exhibit an optical double-peak feature related to local vibrational modes at Ti and Sc sites. The two optical peaks shift from 560 and 640 cm-1 for Ti0.88Sc0.12N to ~= 480 and 570 cm-1 for Ti0.19Sc0.81N with an intensity ratio which is proportional to (1-x)/x. Tc for TiN is 5.4 K and decreases steeply with increasing x to Tc=4.5, 3.4, and 1.9 K with x=0.06, 0.12, and 0.18, respectively. The decrease is due to a reduced DOS at Ef in combination with a weaker effective coupling at higher x. The strong coupling for TiN is related to an anomaly in the longitudinal acoustic branch, which is absent for ScN, in the calculated phonon dispersion curves. Experimental evidence for the vanishing phonon anomaly is supplied by a broadening in the acoustic Raman peak with increasing x.

Gall, D.; Stoehr, M.; Greene, J. E.

2001-11-01

299

Structural, vibrational, and thermodynamic properties of ordered and disordered Ni1-xPtx alloys from first-principles calculations  

NASA Astrophysics Data System (ADS)

In terms of first-principles phonon calculations and the quasiharmonic approach, the structural, vibrational, and thermodynamic properties have been investigated for the ordered and disordered Ni1-xPtx alloys, with the main focus being on disordered Ni0.5Pt0.5. To gain insight into the disordered alloys, we use special quasirandom structures (SQSs) and demonstrate their capabilities in predicting (i) the bond-length distributions, (ii) the phonon spectra, and (iii) the elastic stiffness constants of the disordered alloys. It is found that the Pt-Pt atomic pairs possess the longest bond lengths relative to the Ni-Pt and Ni-Ni ones in the disordered alloys, the predicted force constants indicate that the Pt-Pt bond is stiffer when compared to the Ni-Pt and the Ni-Ni ones for both the ordered and disordered alloys, and the phonon density of states of the disordered alloys are similar to the broadened versions of the ordered cases. Based on the results of the ordered and disordered alloys, a slightly positive deviation from Vegard's law is found for the volume variation of Ni1-xPtx, and correspondingly, a negative deviation is predicted for the change of bulk modulus. With increasing Pt content, the bulk modulus derivative relative to pressure increases approximately linearly, whereas the magnetic moment decreases. In addition, the SQS-predicted relative energies (enthalpies of formation) for the disordered Ni1-xPtx are also compared to cluster expansion predictions. As an application of the finite temperature thermodynamic properties, the phase transition between the ordered L10 and the disordered Ni0.5Pt0.5 is predicted to be 755 ± 128 K, which agrees reasonably well with the measurement ˜900 K, demonstrating that the driving force of the phase transition stems mainly from the configurational entropy rather than the vibrational entropy.

Shang, S. L.; Wang, Y.; Kim, D. E.; Zacherl, C. L.; Du, Y.; Liu, Z. K.

2011-04-01

300

Vibrational spectra and molecular structure of chiral and racemic 4-phenyl-1,3-oxazolidin-2-one by density functional theory and ab initio Hartree-Fock calculations  

NASA Astrophysics Data System (ADS)

The vibrational frequencies and molecular geometry of (R)- and (rac)-4-phenly-1,3-oxazolidin-2-one (4-POO) in the ground state have been calculated using the Hartree-Fock and density functional method (B3LYP) with 6-31G(d) basis set. The optimized geometric bond lengths are described better by HF while bond angles are reproduced more accurately by DFT (B3LYP). Comparison of the observed fundamental vibrational frequencies of (R)-POO and (rac)-4-POO and calculated results by density functional B3LYP and Hartree-Fock methods indicate that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems.

Atalay, Y.; Ucun, F.; Avc?, D.; Ba?o?lu, A.

2006-06-01

301

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

302

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

303

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

PubMed

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

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

2014-01-01

304

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

305

Calculation of gas vibrations due to simultaneous excitations in reciprocating compressor piping systems with allowance for frictional effect and temperature change in the flow  

Microsoft Academic Search

A graphical method for calculation of gas vibrations in piping systems is presented. The method is applied to several examples of the type that occur in practice. The method can deal, in an easily manageable graphic way, with the effects of such things as simultaneous excitation at different points in the system, flow velocity, damping and temperature variations.

Y. N. Chen

1967-01-01

306

Coupled rotor-body vibrations with inplane degrees of freedom  

NASA Technical Reports Server (NTRS)

In an effort to understand the vibration mechanisms of helicopters, the following basic studies are considered. A coupled rotor-fuselage vibration analysis including inplane degrees of freedom of both rotor and airframe is performed by matching of rotor and fuselage impedances at the hub. A rigid blade model including hub motion is used to set up the rotor flaplag equations. For the airframe, 9 degrees of freedom and hub offsets are used. The equations are solved by harmonic balance. For a 4-bladed rotor, the coupled responses and hub loads are calculated for various parameters in forward flight. The results show that the addition of inplane degrees of freedom does not significantly affect the vertical vibrations for the cases considered, and that inplane vibrations have similar resonance trends as do flapping vibrations.

Ming-Sheng, H.; Peters, D. A.

1985-01-01

307

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

308

Blast Vibration: Threshold Values and Vibration Control.  

National Technical Information Service (NTIS)

A proposal for Finnish blast vibration standards and a calculation model for the extent of the zones for building inspection, risk analysis, and vibration measurements are given. The international conclusion is that particle velocity is the best descripti...

R. Vuolio

1990-01-01

309

Harmonic mappings onto stars  

NASA Astrophysics Data System (ADS)

A general version of the Radó-Kneser-Choquet theorem implies that a piecewise constant sense-preserving mapping of the unit circle onto the vertices of a convex polygon extends to a univalent harmonic mapping of the unit disk onto the polygonal domain. This paper discusses similarly generated harmonic mappings of the disk onto nonconvex polygonal regions in the shape of regular stars. Calculation of the Blaschke product dilatation allows a determination of the exact range of parameters that produce univalent mappings.

Duren, Peter; McDougall, Jane; Schaubroeck, Lisbeth

2005-07-01

310

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.  

PubMed

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. PMID:24070285

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

2013-09-21

311

The effect of an infinite plane-wave approximation on calculations for second-harmonic generation in a one-dimensional nonlinear crystal  

NASA Astrophysics Data System (ADS)

In this paper, the second-harmonic generation (SHG) in a one-dimensional nonlinear crystal that is embedded in air is investigated. Previously, the identical configuration was studied in Li Z. Y. et al., Phys. Rev. B, 60 (1999) 10644, without the use of the slowly varying amplitude approximation (SVAA), but by adopting the infinite plane-wave approximation (PWA), despite the fact that this approximation is not quite applicable to such a system. We calculate the SHG conversion efficiency without a PWA, and compare the results with those from the quoted reference. The investigation reveals that conversion efficiencies of SHG as calculated by the two methods appear to exhibit significant differences, and that the SHG may be modulated by the field of a fundamental wave (FW). The ratio between SHG conversion efficiencies as produced by the two methods shows a periodic variation, and this oscillatory behavior is fully consistent with the variation in transmittance of the FW. Quasi-phase matching (QPM) is also studied, and we find that the location of the peak for SHG conversion efficiency deviates from ?d=0, which differs from the conventional QPM results.

Zhao, Jing; Zhao, Li-Ming

2012-05-01

312

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

NASA Astrophysics Data System (ADS)

1:2 B-site cation ordered Ba(Mg1/3Nb2/3)O3 ceramic was synthesized using conventional solid-state reaction at 1600 °C for 12 h. The structure parameters were obtained through Rietveld refinement of X-ray diffraction data. The Raman peak frequencies were obtained by Lorenz fitting on Raman spectrum. Four-parameter semiquantum model was used to fit the infrared (IR) reflectivity spectrum, and the fitted parameters were used to calculate the dielectric permittivity ? and dielectric loss tan?. A total of 9 active Raman and 16 active IR modes were obtained using first-principle calculations based on density functional theory with local density approximation. All of the vibrational modes were assigned and represented by linear combinations of the symmetry coordinates deduced using group theory analysis. The Raman mode with the highest frequency A1g(4) (789 cm-1) can be described as the breathing vibration of NbO6. The IR modes Eu(1) (149 cm-1) and A2u(2) (212 cm-1), which can be described as the twisting vibrations of Ba-MgO6/Ba-NbO6 on the a-b plane and the stretching vibrations of Ba-MgO6/Ba-NbO6 along the c direction, respectively, are the dominant contributing modes to ? and tan?. The dielectric property parameters obtained using IR spectrum fittings, first-principal calculations, and microwave measurements were compared.

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

2014-03-01

313

Effects of hydrogen bonding interactions on the redox potential and molecular vibrations of plastoquinone as studied using density functional theory calculations.  

PubMed

The effects of H-bonding on the redox potential and molecular vibrations of plastoquinone (PQ) that functions as a primary and a secondary quinone electron acceptor (QA and QB, respectively) in photosystem II (PSII) in plants and cyanobacteria were investigated using density functional theory calculations. Calculations were performed on the neutral and semiquinone anion forms of PQ and its H-bonded complexes, which form H-bonds with water molecules, or using amino acid models mimicking the interactions of QA and QB. The calculated redox potential (E(o)) of PQ showed a linear relationship with the number of H-bonds, and the E(o) increased by +100-200 mV with the addition of one H-bond. Vibrational analysis of the model PQ complexes showed that the CO stretching vibrations of neutral PQ are sensitive to the number and symmetry of H-bonding interactions, providing criteria to determine the H-bonding structure. Although no specific trend in the H-bonding dependency was found for anionic PQ, complex spectral features in the CO stretching region due to significant couplings with other PQ vibrations and the vibrations of H-bonding amino acids are useful monitors of the change in the H-bonding structure of anionic PQ in proteins. The calculated E(o) values and infrared spectra of the QA and QB models are consistent with the view that one additional H-bond to QB from D1-Ser264 largely contributes to the redox potential gap between QA and QB in PSII. PMID:24448716

Ashizawa, Ryota; Noguchi, Takumi

2014-05-28

314

Thermodynamics and lattice vibrations of minerals: 4. Application to chain and sheet silicates and orthosilicates  

Microsoft Academic Search

This paper is the fourth in a series relating the lattice vibrational properties to the thermodynamic properties of minerals. The temperature dependence of the harmonic lattice heat capacity is calculated from a model which uses only elastic, crystallographic, and spectroscopic data for the following minerals: calcite, zircon, forsterite, grossular, pyrope, almandine, spessartine, andradite, kyanite, andalusite, sillimanite, clinoenstatite, orthoenstatite, jadeite, diopside,

Susan Werner Kieffer

1980-01-01

315

Energies and Vibrational Frequencies of Gaseous Alkali Halide M2X+ Ions  

Microsoft Academic Search

A potential function describing the interaction between the ions of M2X+ molecules has been developed using a model suggested by Pauling. From this potential the energies and vibrational frequencies have been calculated for these molecules. The harmonic contributions to the bending frequencies are shown to be far from negligible based on this purely ionic model. The entropy and free energy

Thomas A. Milne; Daniel Cubicciotti

1959-01-01

316

Vibrational spectra and structures of the anions of urazole and 4-methylurazole: DFT calculations of the normal modes and the influence of hydrogen bonding.  

PubMed

Solid state IR and Raman as well as aqueous solution state Raman spectra are reported for the anions of urazole and 4-methylurazole, and their N-deuterated derivatives. DFT calculations, at the B3-LYP/cc-pVTZ level, established that the structures and vibrational spectra of both anions can be interpreted using a model that incorporates hydrogen-bonded water molecules, in conjunction with the polarizable continuum solvation method. In the case of the urazole anion it is shown that deprotonation occurs primarily at N1 rather than N4, but there is also evidence for the second tautomer both in the solid state and in aqueous solution. The vibrational spectra were computed at the optimised molecular geometry in each case, enabling normal coordinate analysis, which yielded satisfactory agreement with the experimental IR and Raman data. Computed potential energy distributions of the normal modes provided detailed vibrational assignments. PMID:21257341

Ryall, John P; Dines, Trevor J; Chowdhry, Babur Z; Leharne, Stephen A; Withnall, Robert

2011-03-01

317

Vibrational spectra and structures of the anions of urazole and 4-methylurazole: DFT calculations of the normal modes and the influence of hydrogen bonding  

NASA Astrophysics Data System (ADS)

Solid state IR and Raman as well as aqueous solution state Raman spectra are reported for the anions of urazole and 4-methylurazole, and their N-deuterated derivatives. DFT calculations, at the B3-LYP/cc-pVTZ level, established that the structures and vibrational spectra of both anions can be interpreted using a model that incorporates hydrogen-bonded water molecules, in conjunction with the polarizable continuum solvation method. In the case of the urazole anion it is shown that deprotonation occurs primarily at N1 rather than N4, but there is also evidence for the second tautomer both in the solid state and in aqueous solution. The vibrational spectra were computed at the optimised molecular geometry in each case, enabling normal coordinate analysis, which yielded satisfactory agreement with the experimental IR and Raman data. Computed potential energy distributions of the normal modes provided detailed vibrational assignments.

Ryall, John P.; Dines, Trevor J.; Chowdhry, Babur Z.; Leharne, Stephen A.; Withnall, Robert

2011-03-01

318

Structure of Au40/-1 in the gas phase: A joint geometry relaxed ab initio calculations and vibrationally resolved photoelectron imaging investigation  

NASA Astrophysics Data System (ADS)

We have combined photoelectron velocity-map imaging spectroscopy and high-level ab initio calculations to elucidate the geometries of Au40/-1. Well-resolved ground-state electronic transition was observed in the photoelectron spectrum of Au4- at 446 nm, leading to more accurate electron affinity and vibrational frequencies for the ground state of the neutral Au4-. The pure and vibrationally resolved spectra provide definitive experimental evidence for the resolution of the ground-state gold tetramer in the gaseous phase, with the aid of the ab initio calculations and Franck-Condon simulations. The comprehensive comparisons between the experiment and theoretical calculations suggest that the Y-shaped structure is the global minimum for both the neutral and anionic Au4.

Liu, Zhiling; Qin, Zhengbo; Xie, Hua; Cong, Ran; Wu, Xia; Tang, Zichao

2013-09-01

319

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

320

Vibrational structure of vinyl chloride cation studied by using one-photon zero-kinetic energy photoelectron spectroscopy.  

PubMed

The vibrational structure of vinyl chloride cation, CH(2)CHCl+ (X(2)A' '), has been studied by vacuum ultraviolet (VUV) zero-kinetic energy (ZEKE) photoelectron spectroscopy. Among nine symmetric vibrational modes, the fundamental frequencies of six modes have been determined. The first overtone of the out-of-plane CH(2) twist vibrational mode has been also measured. In addition to these, the combination and overtone bands of the above vibrational modes about 4500 cm(-1) above the ground state have been observed in the ZEKE spectrum. The vibrational band intensities of the ZEKE spectrum can be described approximately by the Franck-Condon factors with harmonic approximation. The ZEKE spectrum has been assigned based on the harmonic frequencies and Franck-Condon factors from theoretical calculations. The ionization energy (IE) of CH(2)CHCl is determined as 80705.5 +/- 2.5 (cm(-1)) or 10.0062 +/- 0.0003 (eV). PMID:17696413

Zhang, Ping; Li, Juan; Mo, Yuxiang

2007-09-01

321

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

322

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

PubMed

The conformational behavior and structural stability of (2E)-3-phenylprop-2-enoic anhydride were investigated by using density functional theory. Seventeen possible stable conformations of the title compound were determined and verified with their calculated vibrational frequencies being all positive. The optimized molecular structure, vibrational wavenumbers, corresponding vibrational assignments of (2E)-3-phenylprop-2-enoic anhydride have been 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 first hyperpolarizability of the title compound is 12×10(-30) esu and is 92.31 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. PMID:24704480

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

2014-07-15

323

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

NASA Astrophysics Data System (ADS)

The conformational behavior and structural stability of (2E)-3-phenylprop-2-enoic anhydride were investigated by using density functional theory. Seventeen possible stable conformations of the title compound were determined and verified with their calculated vibrational frequencies being all positive. The optimized molecular structure, vibrational wavenumbers, corresponding vibrational assignments of (2E)-3-phenylprop-2-enoic anhydride have been 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 first hyperpolarizability of the title compound is 12 × 10-30 esu and is 92.31 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.

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

2014-07-01

324

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

325

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

NASA Technical Reports Server (NTRS)

A linear formulation of rotor airframe coupling intended for vibration analysis in airframe structural design is presented. The airframe is represented by a finite element analysis model; the rotor is represented by a general set of linear differential equations with periodic coefficients; and the connections between the rotor and airframe are specified through general linear equations of constraint. Coupling equations are applied to the rotor and airframe equations to produce one set of linear differential equations governing vibrations of the combined rotor airframe system. These equations are solved by the harmonic balance method for the system steady state vibrations. A feature of the solution process is the representation of the airframe in terms of forced responses calculated at the rotor harmonics of interest. A method based on matrix partitioning is worked out for quick recalculations of vibrations in design studies when only relatively few airframe members are varied. All relations are presented in forms suitable for direct computer implementation.

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

1982-01-01

326

Harmonic force field for nitro compounds.  

PubMed

Molecular simulations leading to sensors for the detection of explosive compounds require force field parameters that can reproduce the mechanical and vibrational properties of energetic materials. We developed precise harmonic force fields for alanine polypeptides and glycine oligopeptides using the FUERZA procedure that uses the Hessian tensor (obtained from ab initio calculations) to calculate precise parameters. In this work, we used the same procedure to calculate generalized force field parameters of several nitro compounds. We found a linear relationship between force constant and bond distance. The average angle in the nitro compounds was 116°, excluding the 90° angle of the carbon atoms in the octanitrocubane. The calculated parameters permitted the accurate molecular modeling of nitro compounds containing many functional groups. Results were acceptable when compared with others obtained using methods that are specific for one type of molecule, and much better than others obtained using methods that are too general (these ignore the chemical effects of surrounding atoms on the bonding and therefore the bond strength, which affects the mechanical and vibrational properties of the whole molecule). PMID:22119786

Bellido, Edson P; Seminario, Jorge M

2012-06-01

327

The natural and forced vibrations of a wheel disc  

NASA Astrophysics Data System (ADS)

A mechanical model for a wheel disc with a flat web, based on Mindlin's plate theory, is considered. First the eigenfrequencies and mode shapes of the wheel are calculated with the assumption that a fixed point on the rim is connected elastically to the rail. Then the forced vibrations of the wheel are considered under the assumption that a harmonic force acts at the contact surface of the wheel and rail. Results are obtained for the point impedance and the acceleration due to a harmonic force as functions of the frequency of the excitation.

Irretier, H.

1983-03-01

328

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

329

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.

330

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

NASA Astrophysics Data System (ADS)

In this work, the vibrational spectral analysis is carried out by using Raman and infrared spectroscopy in the range 100-4000 cm-1and 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 CHdbnd NOH ring are investigated. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule are calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results.

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

2014-01-01

331

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

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

332

Molecular structure and harmonic force field of SbCl3 by microwave spectroscopy  

Microsoft Academic Search

The microwave spectrum of six isotopically substituted molecules of SbCl3 in the frequency range 27-250 GHz has been investigated. Six rs structures were determined resulting in the following average values of the bond length and bond angle: rs(SbCl) = 2.3217 Å thetas(ClSbCl) = 97.19° The harmonic force field of SbCl3 has been calculated using the vibrational frequencies, the mean amplitudes,

G. Cazzoli; W. Caminati

1976-01-01

333

Tautomers and conformers of malonamide, NH2-C(O)-CH2-C(O)-NH2: vibrational analysis, NMR spectra and ab initio calculations.  

PubMed

The conformational and tautomeric compositions of malonamide, NH2-C(O)-CH2-C(O)-NH2 were determined by vibrational spectroscopy and theoretical calculations (HF/6-31G*, B3PW91/6-31G*). Solid state Fourier transform infrared and Raman spectra were analysed. They reveal the existence of a diketo tautomer. Theoretical calculations predict a diketo structure belonging to the C1 symmetry group. No enol form is present in the molecule in the solid. 13C-NMR studies show only signals of a diketo tautomer. PMID:10907882

Schiavoni, M M; Mack, H G; Ulic, S E; Della Védova, C O

2000-07-01

334

Tautomers and conformers of malonamide, NH 2-C(O)-CH 2-C(O)-NH 2: vibrational analysis, NMR spectra and ab initio calculations  

NASA Astrophysics Data System (ADS)

The conformational and tautomeric compositions of malonamide, NH 2-C(O)-CH 2-C(O)-NH 2 were determined by vibrational spectroscopy and theoretical calculations (HF/6-31G*, B3PW91/6-31G*). Solid state Fourier transform infrared and Raman spectra were analysed. They reveal the existence of a diketo tautomer. Theoretical calculations predict a diketo structure belonging to the C 1 symmetry group. No enol form is present in the molecule in the solid. 13C-NMR studies show only signals of a diketo tautomer.

Schiavoni, M. M.; Mack, H.-G.; Ulic, S. E.; Della Védova, C. O.

2000-07-01

335

Dissociative electron attachment and vibrational excitation of H{sub 2} by low-energy electrons: Calculations based on an improved nonlocal resonance model  

SciTech Connect

An improved nonlocal resonance model proposed by Cizek, Horacek, and Domcke [J. Phys. B 31, 2571 (1998)] is used for the calculation of cross sections of electron dissociative attachment and vibrational excitation of molecular hydrogen by the impact of low-energy electrons in the range of {sup 2}{sigma}{sub u}{sup +} resonance. The model is based on ab initio data and takes full account of the nonlocality of the effective potential for the nuclear motion. The dissociative attachment cross sections and rate constants are calculated for all target states (v,J) of relevance and compared with other theoretical and experimental data. It is found that the present dissociative attachment cross section calculated under the conditions of the experiment carried out by Schulz and Asundi reproduces the larger of the two values proposed by them, i.e.-2.8x10{sup -21} cm{sup 2}. A detailed discussion of the dissociative attachment cross section as a function of the vibrational and rotational target states is given. Very narrow peaks, with a width of 1 meV, are observed in the dissociative attachment cross section for large values of the orbital quantum number J. These structures are interpreted as shape resonances in H{sup -}+H collision dynamics. It is shown that for large values of J rotational excitation of the hydrogen molecule enhances the dissociative attachment more efficiently than vibrational excitation. The largest dissociative attachment cross section of 28.3x10{sup -16} cm{sup 2} is obtained for v=1 and J=29. The process of vibrational excitation will be discussed in a separate paper.

Horacek, J.; Cizek, M.; Houfek, K.; Kolorenc, P.; Domcke, W. [Institute of Theoretical Physics, Charles University, Prague (Czech Republic); Department of Chemistry, Technical University of Munich, D-85747 Garching (Germany)

2004-11-01

336

Structural and vibrational study of maprotiline  

NASA Astrophysics Data System (ADS)

Maprotiline ( N-methyl-9,10-ethanoanthracene-9(10H)-propanamine) is a tetra cyclic antidepressant. It is a highly selective inhibitor of norepinephrine reuptake. The solid and solution in CCl 4 and methanol infrared spectra of maprotiline were recorded. The fully optimized equilibrium structure of maprotiline was obtained from DFT calculations by using the B3LYP functional in combination with 6-31G and 6-311G(d,p) basis sets. The results of harmonic and anharmonic frequency calculations on maprotiline were presented. The vibrational spectra were interpreted, with the aid of normal coordinate analysis based on a scaled quantum mechanical (SQM) force field. Vibrational assignment of all the fundamentals was made using the total energy distribution (TED). The possible interaction between maprotiline and neurotransmitter serotonin (5-HT) were investigated.

Yavuz, A. E.; Haman Bayar?, S.; Kazanc?, N.

2009-04-01

337

Determination of radial-forces in relation to noise and vibration problems of squirrel-cage induction motors  

Microsoft Academic Search

The radial electromagnetic forces in induction motors play an important role in the production of audible noise and vibrations. The magnetic flux pulsations at the iron surfaces produce these radial forces, which act on the stator and rotor structures. An analysis for the calculation of the various field harmonics and radial forces in squirrel cage induction motors is presented in

S. P. Verma; A. Balan

1994-01-01

338

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

339

Experimental determinations and quantum-chemical calculations of the vibrational spectra of ?-ZnB4O7 and ?-CaB4O7  

NASA Astrophysics Data System (ADS)

The two oxoborates ?-ZnB4O7 and ?-CaB4O7 were synthesized and investigated by FTIR- and Raman spectroscopy and ab initio quantum chemical calculations. Maximum and mean deviations between experimentally determined bands and calculated modes ranged between 15-36 cm-1 and 5-7 cm-1, respectively, allowing band assignments to vibrational modes in most cases. The complex network structures with tetrahedral BO4 and planar OB3 groups are mirrored by the spectra and numerous vibrational modes, not assignable by standard borates classification schemes. It was confirmed that OB3 units, despite similar force constants and geometry, do not absorb in the same range as BO3 units. Bands in the high wavenumber range are rather caused by B-O-(Zn/Ca), O-B-O, B-O-B, and B-O stretching and bending vibrations. The experimental observation of inactive or Raman-active modes in the absorption spectra indicates defects or structural distortions in both compounds.

Kaindl, Reinhard; Sohr, Gerhard; Huppertz, Hubert

2013-12-01

340

Quasiclassical trajectory calculations for Li(22PJ) + H2 --> LiH(X1?+) + H: Influence by vibrational excitation and translational energy  

NASA Astrophysics Data System (ADS)

Ab initio potential energy surfaces and the corresponding analytical energy functions of the ground 1A' and excited 2A' states for the Li(22P) plus H2 reaction are constructed. Quasiclassical trajectory calculations on the fitted energy functions are performed to characterize the reactions of Li(22P) with H2(v = 0, j = 1) and H2(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 H2(v = 0, j = 1) and H2(v = 1, j = 1) reactions are single-peaked with the maximum population at j' = 7, consistent with the previous observation. The vibrational excitation of H2(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.

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

2011-01-01

341

Experimental determinations and quantum-chemical calculations of the vibrational spectra of ?-ZnB4O7 and ?-CaB4O7.  

PubMed

The two oxoborates ?-ZnB4O7 and ?-CaB4O7 were synthesized and investigated by FTIR- and Raman spectroscopy and ab initio quantum chemical calculations. Maximum and mean deviations between experimentally determined bands and calculated modes ranged between 15-36 cm(-1) and 5-7 cm(-1), respectively, allowing band assignments to vibrational modes in most cases. The complex network structures with tetrahedral BO4 and planar OB3 groups are mirrored by the spectra and numerous vibrational modes, not assignable by standard borates classification schemes. It was confirmed that OB3 units, despite similar force constants and geometry, do not absorb in the same range as BO3 units. Bands in the high wavenumber range are rather caused by B-O-(Zn/Ca), O-B-O, B-O-B, and B-O stretching and bending vibrations. The experimental observation of inactive or Raman-active modes in the absorption spectra indicates defects or structural distortions in both compounds. PMID:23973587

Kaindl, Reinhard; Sohr, Gerhard; Huppertz, Hubert

2013-12-01

342

Harmonic frequency scaling factors for Hartree-Fock, S-VWN, B-LYP, B3-LYP, B3PW91 and MP2 with the Sadlej pVTZ electric property basis set  

Microsoft Academic Search

.   Scaling factors for obtaining fundamental vibrational frequencies from harmonic frequencies calculated at six of the most\\u000a commonly used levels of theory have been determined from regression analysis for the polarized-valence triple-zeta (pVTZ)\\u000a Sadlej electric property basis set. The Sadlej harmonic frequency scaling factors for first- and second-row molecules were\\u000a derived from a comparison of a total of 900 individual

Mathew D. Halls; Julia Velkovski; H. Bernhard Schlegel

2001-01-01

343

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.  

PubMed

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(-30)esu, 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. PMID:24840488

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

2014-10-15

344

Comparison of the performance of different DFT methods in the calculations of the molecular structure and vibration spectra of serotonin (5-hydroxytryptamine, 5-HT)  

NASA Astrophysics Data System (ADS)

Serotonin (5-hydroxytryptamine, 5-HT) is a monoamine neurotransmitter which plays an important role in treating acute or clinical stress. The comparative performance of different density functional theory (DFT) methods at various basis sets in predicting the molecular structure and vibration spectra of serotonin was reported. The calculation results of different methods including mPW1PW91, HCTH, SVWN, PBEPBE, B3PW91 and B3LYP with various basis sets including LANL2DZ, SDD, LANL2MB, 6-31G, 6-311++G and 6-311+G* were compared with the experimental data. It is remarkable that the SVWN/6-311++G and SVWN/6-311+G* levels afford the best quality to predict the structure of serotonin. The results also indicate that PBEPBE/LANL2DZ level show better performance in the vibration spectra prediction of serotonin than other DFT methods.

Yang, Yue; Gao, Hongwei

2012-04-01

345

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

NASA Technical Reports Server (NTRS)

A potential energy surface for the HCN/HNC system which is a fit to extensive, high-quality ab initio, coupled-cluster calculations is presented. All HCN and HNC states with energies below the energy of the first delocalized state are reported and characterized. Vibrational transition energies are compared with all available experimental data on HCN and HNC, including high CH-overtone states up to 23,063/cm. A simulation of the (A-tilde)-(X-tilde) stimulated emission pumping (SEP) spectrum is also reported, and the results are compared to experiment. Franck-Condon factors are reported for odd bending states of HCN, with one quantum of vibrational angular momentum, in order to compare with the recent assignment by Jonas et al. (1992), on the basis of axis-switching arguments of a number of previously unassigned states in the SEP spectrum.

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

1993-01-01

346

Calculation of vibrational energy levels of triatomic molecules with the C 2v and C s symmetries by summing divergent series of the Rayleigh-Schrödinger perturbation theory  

NASA Astrophysics Data System (ADS)

The Rayleigh-Schrödinger perturbation theory is applied to calculation of vibrational energy levels of triatomic molecules with the C 2v and C s symmetries: SO2, H2S, F2O, HOF, HOCl, and DOCl. Particular attention is given to the states coupled by anharmonic resonances; for such states, the perturbation theory series diverge. To sum these series, the known methods of Padé, Padé-Borel, and Padé-Hermite and the method of power moments are used. For low-lying levels, all the summation methods give satisfactory results, while the method of quadratic Padé-Hermite approximants appears to be more efficient for high-excited states. Using these approximants, the structure of singularities of the vibrational energy, as a function in the complex plane, is studied.

Bykov, A. D.; Kalinin, K. V.

2012-03-01

347

Calculations of nonlinear wave-packet interferometry signals in the pump-probe limit as tests for vibrational control over electronic excitation transfer  

NASA Astrophysics Data System (ADS)

The preceding paper [J. D. Biggs and J. A. Cina, J. Chem. Phys. 131, 224101 (2009)] (referred to here as Paper 1), describes a strategy for externally influencing the course of short-time electronic excitation transfer (EET) in molecular dimers and observing the process by nonlinear wave-packet interferometry (nl-WPI). External influence can, for example, be exerted by inducing coherent intramolecular vibration in one of the chromophores prior to short-pulse electronic excitation of the other. Within a sample of isotropically oriented dimers having a specified internal geometry, a vibrational mode internal to the acceptor chromophore can be preferentially driven by electronically nonresonant impulsive stimulated Raman (or resonant infrared) excitation with a short polarized ``control'' pulse. A subsequent electronically resonant polarized pump then preferentially excites the donor, and EET ensues. Paper 1 investigates control-pulse-influenced nl-WPI as a tool for the spectroscopic evaluation of the effect of coherent molecular vibration on excitation transfer, presenting general expressions for the nl-WPI difference signal from a dimer following the action of a control pulse of arbitrary polarization and shape. Electronic excitation is to be effected and its interchromophore transfer monitored by resonant pump and probe ``pulses,'' respectively, each consisting of an optical-phase-controlled ultrashort pulse-pair having arbitrary polarization, duration, center frequency, and other characteristics. Here we test both the control strategy and its spectroscopic investigation-with some sacrifice of amplitude-level detail-by calculating the pump-probe difference signal. That signal is the limiting case of the control-influenced nl-WPI signal in which the two pulses in the pump pulse-pair coincide, as do the two pulses in the probe pulse-pair. We present calculated pump-probe difference signals for (1) a model excitation-transfer complex in which two equal-energy monomers each support one moderately Franck-Condon active intramolecular vibration; (2) a simplified model of the covalent dimer dithia-anthracenophane, representing its EET dynamics following selective impulsive excitation of the weakly Franck-Condon active ?12 anthracene vibration at 385 cm-1 and (3) a model complex featuring moderate electronic-vibrational coupling in which the site energy of the acceptor chromophore is lower than that of the donor.

Biggs, Jason D.; Cina, Jeffrey A.

2009-12-01

348

Ab initio and DFT studies of the vibrational spectra of benzofuran and some of its derivatives  

NASA Astrophysics Data System (ADS)

The vibrational spectra of benzofuran and some of its derivatives have been systematically investigated by ab initio and density functional B3LYP methods. The harmonic vibrational wavenumbers and intensity of vibrational bands were calculated at ab initio and DFT levels invoking different basis sets up to 6-311++g**. Vibrational assignments have been made and it has been found that the calculated DFT frequencies agree well in most cases with the observed frequencies for each molecule. Conformational studies have also been carried out and it is evident from ab initio calculations that 2(3H) benzofuranone is more stable than 3(2H) benzofuranone in support to our earlier semiempirical results.

Singh, V. B.

2006-12-01

349

Ab initio and DFT studies of the vibrational spectra of benzofuran and some of its derivatives.  

PubMed

The vibrational spectra of benzofuran and some of its derivatives have been systematically investigated by ab initio and density functional B3LYP methods. The harmonic vibrational wavenumbers and intensity of vibrational bands were calculated at ab initio and DFT levels invoking different basis sets up to 6-311++g**. Vibrational assignments have been made and it has been found that the calculated DFT frequencies agree well in most cases with the observed frequencies for each molecule. Conformational studies have also been carried out and it is evident from ab initio calculations that 2(3H) benzofuranone is more stable than 3(2H) benzofuranone in support to our earlier semiempirical results. PMID:16716650

Singh, V B

2006-12-01

350

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

351

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.

352

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.

2014-06-01

353

DFT calculations of the structures and vibrational spectra of the [Fe(bpy) 3] 2+ and [Ru(bpy) 3] 2+ complexes  

NASA Astrophysics Data System (ADS)

Structures of the [M(bpy) 3] 2+ complexes (M = Fe and Ru) have been calculated at the B3-LYP/DZVP level. IR and Raman spectra were calculated using the optimised geometries, employing a scaled quantum chemical force field, and compared with an earlier normal coordinate analysis of [Ru(bpy) 3] 2+ which was based upon experimental data alone, and the use of a simplified model. The results of the calculations provide a highly satisfactory fit to the experimental data and the normal coordinate analyses, in terms of potential energy distributions, allow a detailed understanding of the vibrational spectra of both complexes. Evidence is presented for Jahn-Teller distortion in the 1E MLCT excited state.

Alexander, Bruce D.; Dines, Trevor J.; Longhurst, Rayne W.

2008-09-01

354

Structural and vibrational study on zwitterions of L-threonine in aqueous phase using the FT-Raman and SCRF calculations  

NASA Astrophysics Data System (ADS)

Quantum mechanical/molecular mechanics (QM/MM) calculations were performed to study the most stable theoretical structure of L-threonine in an aqueous solution phase and to observe the changes occurring in the structural and vibrational properties of L-threonine in the aqueous media. L-threonine was characterized by Raman spectroscopies in the solid state and in aqueous solution. Optimized geometries and relative stabilities for the monomer and two dimers were calculated using the hybrid B3LYP level taking into account the solvent effects by means of the integral equation formalism of the polarizable continuum model (IEF-PCM). The obtained results in the aqueous solution were compared with those calculated for the monomer in the gas phase. The presence of hydrogen bonding in the monomer of L-threonine was studied by means of the Atoms in Molecules theory (AIM) and natural bond orbital (NBO) studies. The complete assignments of the vibrational spectra of L-threonine in the aqueous solution was performed by using the Pulay's scaled quantum mechanical force field (SQMFF) methodology. Additionaly, hydrated complexes of the monomer considering the interaction with one, two, three and four discrete water molecules were also studied taking into account the solvent effect by using the IEFPCM method. An agreement between theoretical and available experimental results was found.

Guzzetti, Karina Andrea; Brizuela, Alicia Beatriz; Romano, Elida; Brandán, Silvia Antonia

2013-08-01

355

Calculation of the energy levels of excited vibrational states of the HD16O molecule by summing divergent series of the Rayleigh-Schrödinger perturbation theory. The shift of zero-order levels  

NASA Astrophysics Data System (ADS)

The Rayleigh-Schrödinger perturbation theory is applied to calculation of the energy levels of excited vibrational states of the HD16O molecule. The model of coupled anharmonic oscillators is considered, with the anharmonic part of potential energy being taken into account as the perturbation. The calculations are carried out for the vibrational states that correspond to three-to seven-fold vibrational excitations. Since the perturbation series diverge in the case of strong resonance interactions and their approximations by the Padé and Padé-Hermite methods do not yield sufficiently correct results, a calculation technique is applied that allows the zero-order approximation to be modified. The zero-order Hamiltonian is modified by shifting the vibrational frequencies, which decreases the mixing of states. The new Rayleigh-Schrödinger series can be summed using the quadratic Padé-Hermite approximation method.

Bykov, A. D.; Duchko, A. N.; Kalinin, K. V.

2014-04-01

356

Molecular structure, vibrational spectroscopic (FT-IR, FT-Raman), UV and NBO analysis of 2-chlorobenzonitrile by density functional method  

Microsoft Academic Search

In this work, we will report a combined experimental and theoretical study on molecular structure, vibrational spectra, NBO and UV spectral analysis of 2-chlorobenzonitrile (2-ClBN). The FT-IR solid phase (4000–400cm?1), and FT-Raman spectra (3500–50cm?1) of 2-ClBN was recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of 2-ClBN in the ground state have been calculated by using the density

Akhil R. Krishnan; H. Saleem; S. Subashchandrabose; N. Sundaraganesan; S. Sebastain

2011-01-01

357

Ethylenediammonium dication: H-bonded complexes with terephthalate, chloroacetate, phosphite, selenite and sulfamate anions. Detailed vibrational spectroscopic and theoretical studies of ethylenediammonium terephthalate.  

PubMed

Crystalline complexes between ethylenediammonium dication and terephthalate, chloroacetate, phosphite, selenite and sulfamate anions were obtained by slow evaporation from water solution method. Room temperature powder infrared and Raman measurements were carried out. For ethylenediammonium terephthalate theoretical calculations of structure were performed by two ways: ab-initio HF and semiempirical PM3. In this case the PM3 method gave more accurate structure (closer to X-ray results). The additional PM3 calculations of vibrational spectra were performed. On the basis theoretical approach and earlier vibrational studies of similar compounds the vibrational assignments for observed bands have been proposed. All compounds were checked for second harmonic generation (SHG). PMID:23078789

Marchewka, M K; Drozd, M

2012-12-01

358

Ethylenediammonium dication: H-bonded complexes with terephthalate, chloroacetate, phosphite, selenite and sulfamate anions. Detailed vibrational spectroscopic and theoretical studies of ethylenediammonium terephthalate  

NASA Astrophysics Data System (ADS)

Crystalline complexes between ethylenediammonium dication and terephthalate, chloroacetate, phosphite, selenite and sulfamate anions were obtained by slow evaporation from water solution method. Room temperature powder infrared and Raman measurements were carried out. For ethylenediammonium terephthalate theoretical calculations of structure were performed by two ways: ab-initio HF and semiempirical PM3. In this case the PM3 method gave more accurate structure (closer to X-ray results). The additional PM3 calculations of vibrational spectra were performed. On the basis theoretical approach and earlier vibrational studies of similar compounds the vibrational assignments for observed bands have been proposed. All compounds were checked for second harmonic generation (SHG).

Marchewka, M. K.; Drozd, M.

2012-12-01

359

Approximating coupled cluster level vibrational frequencies with composite methods.  

PubMed

An extensive study of the harmonic frequencies of a large set of small polyatomic closed-shell molecules computed at both single level ab initio and composite approximations is presented here. Using various combinations of basis sets, composite methods are capable of predicting single level ab initio CCSD(T) harmonic frequencies to within 5 cm(-1) on average, which suggests a computationally affordable means of obtaining highly accurate vibrational frequencies compared to the CCSD(T) level. A general approach for calculating the composite level equilibrium geometries and harmonic frequencies for polyatomic systems that uses the Collin's method of interpolating potential energy surfaces is also described here. This approach is further tested on tetrafluoromethane, and an estimation of the potential CPU time savings that may be obtained is also presented. It is envisaged that the findings here will enable theoretical studies of fundamental frequencies and energetics of significantly larger molecular systems. PMID:16494391

Fan, Yanping; Ho, Junming; Bettens, Ryan P A

2006-03-01

360

Quasibound continuum states in SiF4 (D2A1) photoionization: photoelectron-vibrational coupling.  

PubMed

The authors report a fully vibrationally resolved photoelectron spectroscopy investigation of a nonplanar molecule studied over a range of excitation energies. Experimental results for all four fundamental vibrational modes are presented. In each case significant non-Franck-Condon effects are seen. The vibrational branching ratio for the totally symmetric mode nu1+ is found to be strongly affected by resonant excitation in the SiF4+ (D2A1) photoionization channel. This is shown to be the result of two distinct shape resonances, which for the first time have been both confirmed by theoretical calculations. Vibrationally resolved Schwinger photoionization calculations are used to understand the vibronic coupling for the photoelectrons, both using ab initio and harmonic vibrational wave functions. PMID:17614551

Montuoro, Raffaele; Lucchese, Robert R; Bozek, John D; Das, Aloke; Poliakoff, E D

2007-06-28

361

Quasibound continuum states in SiF4 (D~ 2A1) photoionization: Photoelectron-vibrational coupling  

NASA Astrophysics Data System (ADS)

The authors report a fully vibrationally resolved photoelectron spectroscopy investigation of a nonplanar molecule studied over a range of excitation energies. Experimental results for all four fundamental vibrational modes are presented. In each case significant non-Franck-Condon effects are seen. The vibrational branching ratio for the totally symmetric mode ?1+ is found to be strongly affected by resonant excitation in the SiF4+ (D~ 2A1) photoionization channel. This is shown to be the result of two distinct shape resonances, which for the first time have been both confirmed by theoretical calculations. Vibrationally resolved Schwinger photoionization calculations are used to understand the vibronic coupling for the photoelectrons, both using ab initio and harmonic vibrational wave functions.

Montuoro, Raffaele; Lucchese, Robert R.; Bozek, John D.; Das, Aloke; Poliakoff, E. D.

2007-06-01

362

Experimental Study of the Vibration Characteristics of Railroad Ties  

NASA Astrophysics Data System (ADS)

Vibration characteristics of railroad ties are investigated by the method of shock excitation. The feasibility of estimating the quality of railroad tracks from the harmonic analysis of these vibrations is demonstrated.

Vasil'Ev, N. A.; Dvornikov, S. I.

2000-05-01

363

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

364

DFT calculation of molecular structure and vibrational spectra of the phosphorus-containing G1? generation dendrimer with terminal aldehyde groups  

NASA Astrophysics Data System (ADS)

The Raman and infrared spectra of the first generation of the phosphorus-containing dendrimer with terminal aldehyde groups have been recorded. The structural optimization and normal mode analysis are performed for phosphorus-containing dendrimer on the basis of the ab initio density functional theory. This calculations gave vibrational frequencies and infrared intensities for the t,g,g- and t,-g,g-conformers of the terminal groups. The t,g,g-conformer is 0.34 kcal/mol less stable compared to t,-g,g-conformer. It is found that the repeated units of dendrimer exists in a single stable conformation with planar sbnd O sbnd C 6H 4sbnd CH dbnd N sbnd N(CH 3) sbnd P fragments. All these observations suggest that steric congestion does not disturb the construction of dendrimers even for the highest generations, and that terminal groups are readily available for further reactions. Relying on DFT calculations a complete vibrational assignment is proposed for different parts of the studied dendrimer. Our study reveals that in the G1' and G 1 dendrimers the most reactive are the terminal groups. IR spectroscopy combined with ab initio DFT computation provides unique detailed information about the structure of the technologically relevant materials, which could not be obtained before with any other technique.

Furer, V. L.; Vandyukov, A. E.; Majoral, J. P.; Caminade, A. M.; Kovalenko, V. I.

2006-08-01

365

Vibrational spectra and theoretical calculations (dimerization, UV-Vis, multinuclear NMR and pes analyses) of 3,4-dimethylbenzamide and 3,4,5-trihydroxybenzamide.  

PubMed

The FT-IR and FT-Raman spectra of 3,4-dimethyl benzamide (DMBA) and 3,4,5-trihydroxy benzamide (THBA) have been measured in the regions 400-4000 and 50-3500 cm(-1), respectively. Utilizing the observed FT-IR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the title compounds were carried out. The vibrational frequencies which were determined experimentally are compared with those theoretical frequencies from force field calculation based on B3LYP/6-311++G(d,p) methods. Stability of the compound arising from hyperconjugative interactions and charge delocalization have been analyzed using natural bond orbital analysis. UV-Vis analysis of the title compounds has also been done using TD-DFT method. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the compounds were calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. HOMO-LUMO and MEP analyses have been done for the title compounds. PMID:24161844

Muniappan, P; Meenakshi, R; Rajavel, G; Arivazhagan, M

2014-01-01

366

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

367

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

368

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

369

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

NASA Astrophysics Data System (ADS)

Difluoromethane (CH2F2, HFC-32) is a molecule used in refrigerant mixtures as a replacement of the more environmentally hazardous, ozone depleting, chlorofluorocarbons. On the other hand, presenting strong vibration-rotation bands in the 9 ?m atmospheric window, it is a greenhouse gas which contributes to global warming. In the present work, the vibrational and ro-vibrational properties of CH2F2, providing basic data for its atmospheric modeling, are studied in detail by coupling medium resolution Fourier transform infrared spectroscopy to high-level electronic structure ab initio calculations. Experimentally a full quantum assignment and accurate integrated absorption cross sections are obtained up to 5000 cm-1. Ab initio calculations are carried out by using CCSD(T) theory and large basis sets of either the correlation consistent or atomic natural orbital hierarchies. By using vibrational perturbation theory to second order a complete set of vibrational and ro-vibrational parameters is derived from the ab initio quartic anharmonic force fields, which well compares with the spectroscopic constants retrieved experimentally. An excellent agreement between theory and experiment is achieved for vibrational energy levels and integrated absorption cross sections: transition frequencies up to four quanta of vibrational excitation are reproduced with a root mean square deviation (RMSD) of 7 cm-1 while intensities are predicted within few km mol-1 from the experiment. Basis set performances and core correlation effects are discussed throughout the paper. Particular attention is focused in the understanding of the anharmonic couplings which rule the vibrational dynamics of the |?1>, |2?8>, |2?2> three levels interacting system. The reliability of the potential energy and dipole moment surfaces in reproducing the vibrational eigenvalues and intensities as well as in modeling the vibrational and ro-vibrational mixings over the whole 400-5000 cm-1 region is also demonstrated by spectacular spectral simulations carried out by using the ro-vibrational Hamiltonian constants, and the relevant coupling terms, obtained from the perturbation treatment of the ab initio anharmonic force field. The present results suggest CH2F2 as a prototype molecule to test ab initio calculations and theoretical models.

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

2012-06-01

370

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

PubMed

Difluoromethane (CH(2)F(2), HFC-32) is a molecule used in refrigerant mixtures as a replacement of the more environmentally hazardous, ozone depleting, chlorofluorocarbons. On the other hand, presenting strong vibration-rotation bands in the 9 ?m atmospheric window, it is a greenhouse gas which contributes to global warming. In the present work, the vibrational and ro-vibrational properties of CH(2)F(2), providing basic data for its atmospheric modeling, are studied in detail by coupling medium resolution Fourier transform infrared spectroscopy to high-level electronic structure ab initio calculations. Experimentally a full quantum assignment and accurate integrated absorption cross sections are obtained up to 5000 cm(-1). Ab initio calculations are carried out by using CCSD(T) theory and large basis sets of either the correlation consistent or atomic natural orbital hierarchies. By using vibrational perturbation theory to second order a complete set of vibrational and ro-vibrational parameters is derived from the ab initio quartic anharmonic force fields, which well compares with the spectroscopic constants retrieved experimentally. An excellent agreement between theory and experiment is achieved for vibrational energy levels and integrated absorption cross sections: transition frequencies up to four quanta of vibrational excitation are reproduced with a root mean square deviation (RMSD) of 7 cm(-1) while intensities are predicted within few km mol(-1) from the experiment. Basis set performances and core correlation effects are discussed throughout the paper. Particular attention is focused in the understanding of the anharmonic couplings which rule the vibrational dynamics of the |?(1)>, |2?(8)>, |2?(2)> three levels interacting system. The reliability of the potential energy and dipole moment surfaces in reproducing the vibrational eigenvalues and intensities as well as in modeling the vibrational and ro-vibrational mixings over the whole 400-5000 cm(-1) region is also demonstrated by spectacular spectral simulations carried out by using the ro-vibrational Hamiltonian constants, and the relevant coupling terms, obtained from the perturbation treatment of the ab initio anharmonic force field. The present results suggest CH(2)F(2) as a prototype molecule to test ab initio calculations and theoretical models. PMID:22697538

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

2012-06-01

371

Molecular orbital calculations on the vibrational spectra of Q 3 T-(OH) species and the hydrolysis of a three-membered aluminosilicate ring  

NASA Astrophysics Data System (ADS)

Force constant analyses of the molecules [(H 3SiO) 3Al-(OH)] 1-, Na +[(H 3SiO) 3Al-(OH)] 1-, [((OH) 3SiO) 3Al-(OH)] 1- [(H 3SiO) 3Si-(OH)],[((OH) 3SiO) 3Si-(OH)],[((OH) 3SiO) 2((OH) 3A10)Si(OH)] 1- and Na + [(H 3SiO ) 2 (H 3Al0) Si- (OH)] 1- have been performed with ab initio molecular orbital calculations to determine the frequencies and H-D shifts of T- (OH) vibrations in Q 3 T- (OH) species where T is a So 4+ or Al 3+. Calculated Q 3 Si-(OH) vibrations are close to the observed value in H 2O-bearing Si0 2 glass. The theoretical Al-(OH) stretching frequency in Na +[ (H 3SiO) 3A1-(OH)] 1- matches the 880 cm - shoulder in the vibrational spectra of hydrous albitic glasses within experimental error. Isotopic substitution of deuterium for hydrogen in the T-(OH) bond results in frequency shifts of less than 25 cm -1 in all cases consistent with the small H-D frequency shifts observed in silica (Mysen and Virgo, 1986) and Na-aluminosilicate glasses (McMillan et al., 1993). Hydrolysis of a three-membered aluminosilicate ring into a trimeric chain (i.e., [H 6SiAl 20 9] 2- + H 2O ? [H 8SiAl 20 10] 2-) was also calculated. Hydrolysis occurs through a pentavalent Al 3+ transition state complex. Calculated energies of the reactants and product in the above reaction predict that the chain configuration is in a marginally lower potential energy state (-36 kJ/mol) than the H 2O-ring dimer. An activation energy of + 171 kJ/mol is predicted between the two species for hydrolysis and +207 kJ/mol for the reverse reaction.

Kubicki, J. D.; Sykes, Dan

1995-12-01

372

Study of structure-activity relationship of enantiomeric, protonated and deprotonated forms of warfarin via vibrational spectroscopy and DFT calculations  

NASA Astrophysics Data System (ADS)

The structure-activity relationship of the anticoagulant drug warfarin were studied by studying two enantiomeric forms (S-form and R-form) of warfarin and its protonated as well as deprotonated structures in aqueous media using density functional theory (DFT). Theoretically computed Raman and IR spectra of all the computed structures were compared and their specific vibrational spectroscopic signatures were discussed. The percentage contributions of individual normal modes of warfarin, which provides direct evidence of the different molecular activity due to change in relative atomic position of atoms in molecule, were investigated through potential energy distribution (PED). The optimized energy and molecular electrostatic potential (MEP) maps show that the S-form of the drug molecules warfarin is energetically more stable than R-form and provides higher docking opportunity for the molecular binding with the receptors in the bio-systems.

Mishra, Alok; Srivastava, Sunil Kumar; Swati, D.

2013-09-01

373

Structural and vibrational spectral investigations of melaminium maleate monohydrate by FTIR, FT-Raman and quantum chemical calculations.  

PubMed

The structural investigations of the molecular complex of melamine with maleic acid, namely melaminium maleate monohydrate have been carried out by quantum chemical methods in addition to FTIR, FT-Raman and far-infrared spectral studies. The quantum chemical studies were performed with DFT (B3LYP) method using 6-31G(**), cc-pVDZ and 6-311++G(**) basis sets to determine the energy, structural and thermodynamic parameters of melaminium maleate monohydrate. The hydrogen atom from maleic acid was transferred to the melamine molecule giving the singly protonated melaminium cation. The ability of ions to form spontaneous three-dimensional structure through weak OH···O and NH···O hydrogen bonds shows notable vibrational effects. PMID:23416913

Arjunan, V; Kalaivani, M; Marchewka, M K; Mohan, S

2013-04-15

374

Structural and vibrational spectral investigations of melaminium maleate monohydrate by FTIR, FT-Raman and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

The structural investigations of the molecular complex of melamine with maleic acid, namely melaminium maleate monohydrate have been carried out by quantum chemical methods in addition to FTIR, FT-Raman and far-infrared spectral studies. The quantum chemical studies were performed with DFT (B3LYP) method using 6-31G**, cc-pVDZ and 6-311++G** basis sets to determine the energy, structural and thermodynamic parameters of melaminium maleate monohydrate. The hydrogen atom from maleic acid was transferred to the melamine molecule giving the singly protonated melaminium cation. The ability of ions to form spontaneous three-dimensional structure through weak Osbnd H⋯O and Nsbnd H⋯O hydrogen bonds shows notable vibrational effects.

Arjunan, V.; Kalaivani, M.; Marchewka, M. K.; Mohan, S.

2013-04-01

375

A novel touch probe triggered by harmonic generation the International Conference on Control, Automation and Systems 2008 (ICCAS 2008)  

Microsoft Academic Search

A new type of touch probe for measuring small optical parts is proposed. The probe is excited by a piezoelectric actuator in sinusoidal waveform. When the vibrating probe touches an object, harmonic components of the vibration appear in the power spectrum of the probe vibration. When the power of the second harmonic exceeds a threshold level, it is judged that

H. Mizumoto; M. Imai; Y. Yabuta; S. Arii

2008-01-01

376

Damping and acoustic harmonics in cracked laminated composites  

NASA Astrophysics Data System (ADS)

This article reports on a novel experimental technique conceived and used to study damping and generation of acoustic harmonics in a cracked laminated composite. The cracked jaws of a double cantilever specimen with an interlaminar crack were vibrated symmetrically at 22.5 kHz; damping in the specimen and acoustic harmonics in the vicinity of the crack tip were measured as functions of amplitude of vibration. At low amplitudes, the damping was linear (i.e., independent of amplitude) with no detectable acoustic harmonics. At high amplitudes, the damping was nonlinear with generation of acoustic harmonics up to the fifth. Among known models for harmonic generation, the best choice to explain these data seems to be smooth motion of dislocations in graphite vibrating within a potential well of small asymmetry.

Thumma, K. R.; Beshers, D. N.

1995-11-01

377

Molecular structure and vibrational IR spectra of the 2- hydroxypyridine 2(1H)- pyridinone system and its thio and seleno analogs: density functional theory versus conventional ab initio calculations  

Microsoft Academic Search

The molecular parameters (optimized geometries, rotational constants, dipole moments) and vibrational IR spectra (harmonic wavenumbers, absolute intensities) of the 2-hydroxypyridine2(1H)-pyridinone (2OHP2OP) system and its thio (2SHP2SP) and seleno analogs (2SeHP2SeP) are predicted by density functional theory (DFT) with the Becke3-LYP functionals (DFT(B3-LYP) method) using a valence split double-? basis set augmented by polarization functions on all atoms. The results are

Józef S. Kwiatkowski; Jerzy Leszczynski

1996-01-01

378

The use of harmonic analysis of the strain response in Pb(Mg(1/3)Nb(2/3)) O3-based ceramics to calculate electrostrictive coefficients.  

PubMed

The electromechanical response of ceramics has long been described with Landau Devonshire phenomenology, wherein the strain response is linked to a polynomial expansion in electric field or dielectric displacement. Consequently, the electromechanical response has been modeled with a variety of basis functions. However, these models have failed to accommodate hysteresis and the harmonic response that arises with saturation phenomena. In addition, no quantitative criterion has been used to truncate the expansion. By implementing a discrete Fourier transform in conjunction with Devonshire phenomenology, these three problems can be overcome as demonstrated with a dielectrically aged, lead magnesium niobate relaxor ferroelectric well above its Tmax, i.e., operating in the electrostrictive regime. PMID:11800115

DiAntonio, C B; Williams, F A; Pilgrim, S M

2001-11-01

379

First-principles calculations of electronic, vibrational, and structural properties of scheelite EuWO4 under pressure  

NASA Astrophysics Data System (ADS)

In this paper we report a density functional study of the structural, electronic, and vibrational properties of the EuWO4 compound in the scheelite structure. We use Raman spectroscopy to complement the study for this phase at ambient pressure. The first part of the paper is devoted to analyzing the results obtained with the Perdew-Burke-Ernzerhof for solids exchange-correlation functional within the GGA+U approximation and compare those with our experimental results and reported available data. We also present the evolution of these properties, for the same crystal structure, up to 8 GPa. The second part of the paper is devoted to discussing our study on the high-pressure phase transitions of EuWO4, for which we follow the evolution of the structural properties as a function of pressure. The results show that the high-pressure behavior of EuWO4 is very similar to that of CaWO4, SrWO4, BaWO4, and PbWO4, for which the scheelite structure undergoes a phase transition to the fergusonite structure, an observation also supported by our experimental data. Additionally, we can also conclude that at higher pressures, EuWO4 evolves to the BaWO4-II and Cmca crystal phases.

López-Moreno, S.; Rodríguez-Hernández, P.; Muñoz, A.; Romero, A. H.; Errandonea, D.

2011-08-01

380

Numerical analysis of the hybrid transducer ultrasonic motor: comparison of characteristics calculated by transmission-line and lumped-element models.  

PubMed

In this paper, a hybrid transducer ultrasonic motor is numerically analyzed by using two equivalent electrical circuit models. A transmission-line model for the torsional vibration in the stator, which can model any torsional vibration mode and their combinations, was introduced and compared with a lumped-element model, which modeled the fundamental torsional resonance mode in the stator. The calculation result by using the transmission-line model demonstrated that the second harmonic torsional vibration increased either with the static spring force by which the rotor was pressed to the stator or with the load torque placed on the rotor. The difference in the calculated motor performance between the two models appeared when the second harmonic torsional vibration became large at a sufficient static spring force. PMID:12109546

Satonobu, Jun; Friend, James R; Nakamura, Kentaro; Ueha, Sadayuki

2002-06-01

381

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

PubMed

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. PMID:25053310

Schröder, Markus; Meyer, Hans-Dieter

2014-07-21

382

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

383

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

384

Vibrational assignments, normal coordinate analysis, B3LYP calculations and conformational analysis of methyl-5-amino-4-cyano-3-(methylthio)-1H-pyrazole-1-carbodithioate.  

PubMed

The Raman and infrared spectra of solid methyl-5-amino-4-cyano-3-(methylthio)-1H-pyrazole-1-carbodithioate (MAMPC, C7H8N4S3) were measured in the spectral range of 3700-100 cm(-1) and 4000-200 cm(-1) with a resolution of 4 and 0.5 cm(-1), respectively. Room temperature 13C NMR and (1)H NMR spectra from room temperature down to -60 °C were also recorded. As a result of internal rotation around C-N and/or C-S bonds, eighteen rotational isomers are suggested for the MAMPC molecule (Cs symmetry). DFT/B3LYP and MP2 calculations were carried out up to 6-311++G(d,p) basis sets to include polarization and diffusion functions. The results favor conformer 1 in the solid (experimentally) and gaseous (theoretically) phases. For conformer 1, the two -CH3 groups are directed towards the nitrogen atoms (pyrazole ring) and CS, while the -NH2 group retains sp2 hybridization and C-CN bond is quasi linear. To support NMR spectral assignments, chemical shifts (?) were predicted at the B3LYP/6-311+G(2d,p) level using the method of Gauge-Invariant Atomic Orbital (GIAO) method. Moreover, the solvent effect was included via the Polarizable Continuum Model (PCM). Additionally, both infrared and Raman spectra were predicted using B3LYP/6-31G(d) calculations. The recorded vibrational, 1H and 13C NMR spectral data favors conformer 1 in both the solid phase and in solution. Aided by normal coordinate analysis and potential energy distributions, confident vibrational assignments for observed bands have been proposed. Moreover, the CH3 barriers to internal rotations were investigated. The results are discussed herein are compared with similar molecules whenever appropriate. PMID:21676648

Mohamed, Tarek A; Hassan, Ali M; Soliman, Usama A; Zoghaib, Wajdi M; Husband, John; Hassan, Saber M

2011-09-01

385

Vibrational and electronic investigations, thermodynamic parameters, HOMO and LUMO analysis on crotonaldehyde by ab initio and DFT methods  

Microsoft Academic Search

The energy, geometrical parameters and vibrational wavenumbers of crotonaldehyde were calculated by using ab initio and B3LYP with 6-31G(d,p) and 6-311G(d,p) basis sets. The FT-IR and FT-Raman spectra for liquid state crotonaldehyde have been recorded in the region 3400–400cm?1 and 3400–100cm?1, respectively and compared with the theoretical spectrographs constructed from the scaled harmonic vibrational frequencies calculated at HF and DFT

A. Jayaprakash; V. Arjunan; Sujin P. Jose; S. Mohan

2011-01-01

386

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

NASA Astrophysics Data System (ADS)

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

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

1994-01-01

387

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

Microsoft Academic Search

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

Soni Mishra; Poonam Tandon

2012-01-01

388

Dynamics of a Small Globular Protein in Terms of Low-Frequency Vibrational Modes  

Microsoft Academic Search

Normal modes of low-frequency vibrations are calculated for a small globular protein, bovine pancreatic trypsin inhibitor. In modes with frequencies below 120 cm-1 the protein molecule behaves like a continuous elastic body. Most modes with frequencies above 50 cm-1 are shown to behave harmonically within the range of thermal fluctuations at room temperature. Those with frequencies below 50 cm-1 show

Nobuhiro Go; Tosiyuki Noguti; Testuo Nishikawa

1983-01-01

389

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

390

Principal Trajectories of Forced Vibrations  

Microsoft Academic Search

\\u000a As shown earlier by Zhuravlev (1992) that harmonically loaded linear conservative systems possess an alternative physically\\u000a reasonable basis, which is generally different from that associated with conventional principal coordinates. Briefly, such\\u000a a basis determines directions of harmonic loads along which the system response is equivalent to a single oscillator. The\\u000a corresponding definition (principal directions of forced vibrations) is loosing sense

Valery Pilipchuk

391

Ab initio molecular orbital calculations on the associated complexes of lithium cyanide with ammonia  

Microsoft Academic Search

Ab initio molecular orbital (MO) calculations with the 3-21G and 6-31G basis sets are carried out on a series of complexes of NHâ with Li{sup +}, C{triple_bond}N⁻, LiCN, and its isomer LiNC. The BSSE-corrected interaction energies, geometrical parameters, internal force constants, and harmonic vibrational frequencies are evaluated for 15 species. Complexes with trifurcated (C{sub 3v}) structures are calculated to be

P. Mohandas; M. C. Shivaglal; J. Chandrasekhar; Surjit Singh

1995-01-01

392

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

NASA Astrophysics Data System (ADS)

FT Raman and IR spectra of the biologically active molecule, 1-naphthalene acetamide (NA) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers of NA have been calculated with the help of B3LYP density functional theory (DFT) method. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The downshifting of NH 2 stretching wavenumber indicates the formation of intermolecular N-H⋯O hydrogen bonding. The NBO analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule.

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

2010-02-01

393

An accurate calculation of the polarizability of the hydrogen molecule and its dependence on rotation, vibration and isotopic substitution  

Microsoft Academic Search

A variation-perturbation method has been used to calculate the static dipole polarizabilities alpha|| and alpha? of the hydrogen molecule over the bond length range 0·6 a0 ˇ- R ˇ- 10·0 a0. The unperturbed wavefunction consisted of an expansion of 80 terms and the first order perturbed wavefunction consisted of an expansion of 65 terms. These wavefunctions take explicit account of

J. Rychlewski

1980-01-01

394

First-principles pseudopotential calculations for hydrogen in 4d transition metals. II. Vibrational states for interstitial hydrogen isotopes  

Microsoft Academic Search

For pt.I see ibid. vol.4, p.5189 (1992). In this second part of the authors' first-principles study of hydrogen in transition metals within the framework of the Born-Oppenheimer and the local density-functional approximations, the mixed-basis pseudopotential method, which was outlined in the first part, is applied to calculate total energies and internal forces in PdnH supercells with n

C. Elsasser; K. M. Ho; C. T. Chan; M. Fahnle

1992-01-01

395

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

396

Theoretical calculation of the OH vibrational overtone spectra of 1,5-pentanediol and 1,6-hexanediol.  

PubMed

It is well-known that intramolecular hydrogen bonding affects the relative energetics of conformers, as well as the OH stretching peak positions, intensities, and width. In this study we simulated the ?v(OH) = 3, 4 overtone spectra of 1,5-pentanediol (PeD) and 1,6-hexanediol (HD) using the peak positions, intensities, and width calculated from the B3LYP/6-31+G(d,p) method. Furthermore, room temperature free energy calculations were performed using B3LYP/6-31+G(d,p) MP2/6-31+G(d,p), and MP2/6-311++G(3df,3pd) to obtain the relative population of the conformers. From the calculation of 109 and 381 distinct conformers for PeD and HD, respectively, we find that for these long chain diols the intramolecular hydrogen bonded conformers are not the most dominant conformation at room temperature. This is in stark contrast with shorter chain diols such as ethylene glycol for which the hydrogen bonded conformer dominates the population at room temperature. On the other hand, we found that the correlation between the hydrogen bonded OH red shift versus the homogeneous width, ? = 0.0155(??)(1.36), which was derived for shorter chain diols, is valid even for these longer chain diols. We also showed that the intramolecular hydrogen bonded OH initially decays through the CCOH torsion and COH bending mode no matter how long the alkanediol chain length is for 1,n-alkanediols for n up to 6. PMID:22066681

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

2011-12-22

397

Charge transfer in systems of conjugated bonds in cyanobiphenyl molecules: Quantum-chemical calculations of the structure and vibrational spectra  

Microsoft Academic Search

Quantum-chemical calculations of the IR absorption spectra and geometric and electronic structure of cyanobiphenyl molecules\\u000a \\u000a (I) were performed for various angles between benzene ring planes by the B3LYP\\/6-31+G** method. It was shown that the stablest\\u000a conformation of I (X=OCH3, OC3H7) should be the twist conformation with ?= 37°, which was in agreement with the gas-phase experimental data. Rotation of benzene

A. N. Isaev; P. P. Shorygin

2009-01-01

398

Experimental and theoretical study of the vibrational spectra of 12-thiacrown-4 and 18-thiacrown-6, evaluation of the performance of the different anharmonic force fields compared to the scaled quantum mechanical force fields.  

PubMed

We report, to the best of our knowledge, for the first time the vibrational, IR and Raman, spectra of 12-thiacrown-4 (12t4) and 18-thiacrown-6 (18t6). To predict in what conformation 12t4 and 18t6 exist, for the vibrational analysis of both molecules and to assess the performance of the different computational methods for the accurate prediction of the vibrational frequencies of relatively large molecules, the computations were done using the harmonic and anharmonic force fields using the 6-31G* and 6-311G** basis sets. The computations were performed at the HF, B3LYP, CAM-B3LYP, BLYP, BP86, G96LYP, PBE1PBE, TPSSH and MP2 levels. Comparison was made between the calculated and experimental vibrational frequencies as indicated by the root-mean-square (rms) deviations, using either the unscaled and scaled harmonic vibrational frequencies and, unscaled, anharmonic vibrational frequencies. For the harmonic vibrational frequencies two scaling schemes were used. One uses one-scale-factor (1SF) scaling and the other uses 8SF scaling. In terms of the vibrational analysis of 12t4 and 18t6, the report confirms the solid state X-ray structure of D4 of 12t4 and C2 of 18t6. It is concluded that a lower rms deviation is obtained using 1SF scaled harmonic vibrational frequencies at even the HF/6-31G* level than using anharmonic vibrational frequencies at the MP2/6-311G** level. The CAM-B3LYP method showed some improvement over the traditional B3LYP method. PMID:23978743

Al-Jallal, Nada A; Al-Badri, Nada I; El-Azhary, Adel A

2013-12-01

399

Experimental and theoretical study of the vibrational spectra of 12-thiacrown-4 and 18-thiacrown-6, evaluation of the performance of the different anharmonic force fields compared to the scaled quantum mechanical force fields  

NASA Astrophysics Data System (ADS)

We report, to the best of our knowledge, for the first time the vibrational, IR and Raman, spectra of 12-thiacrown-4 (12t4) and 18-thiacrown-6 (18t6). To predict in what conformation 12t4 and 18t6 exist, for the vibrational analysis of both molecules and to assess the performance of the different computational methods for the accurate prediction of the vibrational frequencies of relatively large molecules, the computations were done using the harmonic and anharmonic force fields using the 6-31G* and 6-311G** basis sets. The computations were performed at the HF, B3LYP, CAM-B3LYP, BLYP, BP86, G96LYP, PBE1PBE, TPSSH and MP2 levels. Comparison was made between the calculated and experimental vibrational frequencies as indicated by the root-mean-square (rms) deviations, using either the unscaled and scaled harmonic vibrational frequencies and, unscaled, anharmonic vibrational frequencies. For the harmonic vibrational frequencies two scaling schemes were used. One uses one-scale-factor (1SF) scaling and the other uses 8SF scaling. In terms of the vibrational analysis of 12t4 and 18t6, the report confirms the solid state X-ray structure of D4 of 12t4 and C2 of 18t6. It is concluded that a lower rms deviation is obtained using 1SF scaled harmonic vibrational frequencies at even the HF/6-31G* level than using anharmonic vibrational frequencies at the MP2/6-311G** level. The CAM-B3LYP method showed some improvement over the traditional B3LYP method.

Al-Jallal, Nada A.; Al-Badri, Nada I.; El-Azhary, Adel A.

2013-12-01

400

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

401

Vibrational spectra and structures of urazole and 4-methylurazole: DFT calculations of the normal modes in aqueous solution and in the solid state, and the influence of hydrogen bonding  

NASA Astrophysics Data System (ADS)

Solid-state IR and Raman as well as aqueous solution state Raman spectra are reported for urazole, 4-methylurazole and their deuterated derivatives. DFT calculations, at the B3-LYP/cc-pVTZ level, established that the structures and vibrational spectra of the molecules can be interpreted using models with hydrogen-bonded water molecules, in conjunction with the polarizable continuum solvation method. The vibrational spectra were computed at the optimised molecular geometry in each case, enabling normal coordinate analysis, which yielded satisfactory agreement with the experimental IR and Raman data. Computed potential energy distributions of the normal modes provided detailed vibrational assignments. Solid-state pseudopotential-plane-wave DFT calculations, using the PW91 functional were also carried out, reflecting the importance of intermolecular hydrogen bonding in the solid state.

Ryall, John P.; Dines, Trevor J.; Chowdhry, Babur Z.; Leharne, Stephen A.; Withnall, Robert

2010-08-01

402

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

403

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

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

404

Structural, vibrational, electronic, NMR and reactivity analyses of 2-amino-4H-chromene-3-carbonitrile (ACC) by ab initio HF and DFT calculations  

NASA Astrophysics Data System (ADS)

This study represents an integrated approach towards understanding the vibrational, electronic, NMR, reactivity and structural aspects of 2-amino-4H-chromene-3-carbonitrile (ACC). A detailed interpretation of the FT IR, UV and NMR spectra were reported. Theoretical calculations were performed by ab initio HF and density functional theory (DFT)/B3LYP method using 6-311 + +G(d,p) basis sets. The electronic properties was also studied and the most prominent transition corresponds to ? ? ?*. The lower frontier orbital energy gap and high dipole moment illustrates the high reactivity of the title molecule. The NMR results indicated that the observed chemical shifts depend not only on the structure of the molecule being studied, but also on the solvent used. ACC exhibited good nonlinear optical activity and was much greater than that of urea. Molecular electrostatic potential (MEP) results predicted that the enaminonitrile fragment of ACC to be the most reactive site for both electrophilic and nucleophilic attack. In addition, the thermodynamic properties of the compound were calculated at different temperatures and corresponding relations between the properties and temperature were also studied.

Sridevi, C.; Shanthi, G.; Velraj, G.

2012-04-01

405

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

406

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

407

Optimized Structure and Vibrational Properties by Error Affected Potential Energy Surfaces  

PubMed Central

The precise theoretical determination of the geometrical parameters of molecules at the minima of their potential energy surface and of the corresponding vibrational properties are of fundamental importance for the interpretation of vibrational spectroscopy experiments. Quantum Monte Carlo techniques are correlated electronic structure methods promising for large molecules, which are intrinsically affected by stochastic errors on both energy and force calculations, making the mentioned calculations more challenging with respect to other more traditional quantum chemistry tools. To circumvent this drawback in the present work, we formulate the general problem of evaluating the molecular equilibrium structures, the harmonic frequencies, and the anharmonic coefficients of an error affected potential energy surface. The proposed approach, based on a multidimensional fitting procedure, is illustrated together with a critical evaluation of systematic and statistical errors. We observe that the use of forces instead of energies in the fitting procedure reduces the statistical uncertainty of the vibrational parameters by 1 order of magnitude. Preliminary results based on variational Monte Carlo calculations on the water molecule demonstrate the possibility to evaluate geometrical parameters and harmonic and anharmonic coefficients at this level of theory with an affordable computational cost and a small stochastic uncertainty (<0.07% for geometries and <0.7% for vibrational properties).

Zen, Andrea; Zhelyazov, Delyan; Guidoni, Leonardo

2013-01-01

408

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

409

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

410

New marine harmonic standards  

Microsoft Academic Search

To address concerns associated with electrical power system harmonic distortion on ships and offshore oil rigs and platforms, marine regulating bodies have introduced strict new harmonic standards. These standards define the acceptable level of harmonic voltage distortion allowed on the vessels they certify. High-harmonic distortion levels are appearing as a result of the increased use of power-electronic drive converters for

Tony Hoevenaars; Ian Evans; Andy Lawson

2010-01-01

411

Vibrational dispersion interactions in van der Waals complexes: Effect upon stability and infrared spectra  

SciTech Connect

The vibrational analogue of London dispersion forces has been studied for a generalized bimolecular complex, and calculations have been performed for a series of van der Waals complexes comprised of subunits CO{sub 2}, C{sub 2}H{sub 4}, and HCN. The authors present a generalized nonempirical perturbational methodology for evaluating the second-order stabilization resulting from the correlation between instantaneous monomeric vibrational motions using the harmonic approximation. They find that these second-order energies are typically on the order of 0.01 cm{sup {minus}1}, with the relative ordering (CO{sub 2}){sub 2} > (CO{sub 2}-HCN) > (HCN-C{sub 2}H{sub 4}) > (C{sub 2}H{sub 4}){sub 2}. In conjunction with first-order resonance energies, the shift in monomer vibrational energy levels upon complexation is evaluated. They conclude that although the effect of vibrational dispersion upon the stability of a complex is quite small, its effect upon infrared spectra can be potentially significant. The formalisms for electronic and vibrational dispersion are compared and contrasted. The limitations of this nonempirical scheme for the calculation of vibrational dispersion energies are discussed in light of the approximations that are needed to make the calculations tractable and applicable to large systems.

Glauser, W.A.; Koszykowski, M.L. (Sandia National Labs., Livermore, CA (United States))

1991-10-31

412

Molecular geometries, vibrational analysis, bonding and molecular orbitals of the three isomers of [RuCl(qn) 2NO] (Hqn=2-methyl-8-quinolinol or 2-chloro-8-quinolinol): density functional theory studies  

Microsoft Academic Search

The geometries of the three isomers of [RuCl(qn)2NO] {Hqn=2-methyl-8-quinolinol (H2mqn) or 2-chloro-8-quinolinol (H2cqn)} were calculated with the restricted Hartree–Fock and different DFT methods. The B3PW91 method gave the best performance in the calculation for predicting the structure and vibrational spectrum of this series of complexes. The deviation between the calculated and the observed NO harmonic stretching frequencies was about 1%

Hongfei Wang; Eiichi Miki; Suyong Re; Hiroaki Tokiwa

2002-01-01

413

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

NASA Technical Reports Server (NTRS)

The vibroacoustical characteristics of different types of electric motors are discussed. It is shown that the basic source of low frequency vibrations is rotor unbalance. A flexible damping support, with an antivibrator, is used to obtain the vibroacoustical effect of reduction in the basic harmonic of the electric motor. A model of the electric motor and the damping apparatus is presented. Mathematical models are developed to show the relationships of the parameters. The basic purpose in using a calculation model id the simultaneous replacement of the exciting force created by the rotor unbalance and its inertial rigidity characteristics by a limiting kinematic disturbance.

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

1973-01-01

414

An algorithm of the harmonics on traction power system of the electrified railway  

Microsoft Academic Search

The authors explore harmonic calculations for Chinese electrified railway systems. One of the branches of the electrified railway power system in operation was emulated and calculated with special purpose software for analyzing harmonic currents. The multiple harmonic sources and the asymmetry of the system make the harmonic analysis complicated. The three-phase power system is converted into a single-phase network with

Pan Yinxuan; Sun Shugin; Li Chunhua

1990-01-01

415