Performance of different density functionals for the calculation of vibrational frequencies with vibrational coupled cluster method in bosonic representation (original) (raw)
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Journal of Molecular Structure: THEOCHEM, 2006
The scaling factors for the vibrational frequencies and zero-point vibrational energies evaluated at various combinations of recently developed exchange-correlation functionals and various basis sets are reported. The exchange-correlation functionals considered are B972, B98, HCTH, OLYP, O3LYP, G96LYP, PBE0 and VSXC functionals; the basis sets employed are 3-21G, 6-31G*, 6-31G**, 6-31CG, 6-311G*, 6-311G**, 6-311G(df,p), 6-311CG(df,p), cc-pVDZ and aug-cc-pVDZ. The experimental harmonic frequencies of 122 small molecules and the zero-point vibrational energies of 39 small molecules are used to determine the scaling factors through the least-square fitting procedure. It was found that the scaling factors do not depend significantly on the basis sets considered. The vibrational frequency scaling factors evaluated by using the B98 and PBE0 functionals are recommended on the basis of smallest root mean square error. The zero-point vibrational energy scaling factors evaluated from the B972 functional with Pople's double-zeta basis set and the HCTH functional with Pople's triple-zeta basis set are recommended on the basis of smallest root mean square error. q
Journal of Molecular Modeling, 2015
The present work provides sets of correction factors to adjust the calculated vibrational frequencies of a series of α, ω-diamines hydrochloride salts to account for the intermolecular interactions with the counterion. The study was performed using different theory levels for predicting the vibrational data of isolated dicationic α,ω-diamines and their hydrochloride forms, with and without the explicit account of the interactions with the chloride counterions. Different sets of correction factors were determined for each theory level considering the four smallest elements for the α,ω-diamines series, while their transferability and reliability was evaluated considering the larger elements of the series. The theory level simplification was also evaluated and was found to neither compromise the vibrational frequencies estimates nor the magnitude and accuracy of the pre-defined scaling factors. This suggests that transferability of the correction factors is possible not only for different diamines but also between different levels of theory with the averaged group correction factor, ζ g a , being the best choice to account for the effects of the N-H•••Cl interactions. The possibility of simplifying the theory level without compromising efficiency and accuracy is additionally of utmost importance. This computational approach can constitute a valuable tool in the future for studying the hydrochloride forms of larger and more complex diamine systems.
The Journal of Physical Chemistry A, 2014
The role played by the C*−H based modes (C* being the chiral carbon atom) and 12 the large amplitude motions in the vibrational absorption (VA) and vibrational circular dichroism 13 (VCD) spectra is investigated. The example of an adduct of dimethyl fumarate and anthracene, i.e., 14 dimethyl-(+)-(11R,12R)-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylate, and two deu-15 terated isotopomers thereof specially synthesized for this goal, are considered. By comparing the 16 experimental and DFT calculated spectra of the undeuterated and deuterated species, we 17 demonstrate that (1) the C*−H bending, rocking, and stretching modes in the VA and VCD 18 spectra are clearly identified in well defined spectroscopic features; (2) significant information 19 about the conformer distribution is gathered by analyzing the VA and VCD data of both the 20 fingerprint and the C−H stretching regions, with particular attention paid to the band shape data. 21 Effects related to the large amplitude motions of the two methoxy moieties have been simulated by 22 performing linear transit (LT) calculations, which consists of varying systematically the relative 23 positions of the two methoxy moieties and calculating VCD spectra for the partially optimized 24 structures obtained in this way. The LT method allows one to improve the quality of calculated spectra, as compared to 25 experimental results, especially in regard to relative intensities and bandwidths.
Journal of Computational Chemistry, 2004
The problem of numerical accuracy in the calculation of vibrational frequencies of crystalline compounds from the hessian matrix is discussed with reference to ␣-quartz (SiO 2 ) as a case study and to the specific implementation in the CRYSTAL code. The Hessian matrix is obtained by numerical differentiation of the analytical gradient of the energy with respect to the atomic positions. The process of calculating vibrational frequencies involves two steps: the determination of the equilibrium geometry, and the calculation of the frequencies themselves. The parameters controlling the truncation of the Coulomb and exchange series in Hartree-Fock, the quality of the grid used for the numerical integration of the Exchange-correlation potential in Density Functional Theory, the SCF convergence criteria, the parameters controlling the convergence of the optimization process as well as those controlling the accuracy of the numerical calculation of the Hessian matrix can influence the obtained vibrational frequencies to some extent. The effect of all these parameters is discussed and documented. It is concluded that with relatively economical computational conditions the uncertainty related to these parameters is smaller than 2-4 cm Ϫ1 . In the case of the Local Density Approximation scheme, comparison is possible with recent calculations performed with a Density Functional Perturbation Theory method and a plane-wave basis set.
Vibrational frequency analysis of CH3Cl molecule; ab initio study
Himalayan Physics, 2015
First-principles calculations implemented by Gaussian 09 sets of programs has been performed in order to study the stability, electronic properties, nature of bonding and vibrational frequency assignments for CH3Cl molecule using QCISD levels of approximation with the choice of basis set 6-31G(d, p). Quantum Theory of Atoms In Molecule (QTAIM) approach has been adopted for bonding analysis and HOMO, LUMO energies were taken as the central aspects for discussing the chemical reactivity of the studied system. The vibrational frequency shift due to isotopic substitution of C-atom and Cl-atom in title molecule has been discussed. The Himalayan Physics Year 5, Vol. 5, Kartik 2071 (Nov 2014)Page: 142-145
Calculated vibrational spectra for CHnOHm species
Journal of Physical Chemistry a, 2000
There is a lack of reference vibrational spectra in the literature for many species that have been postulated to form on metal surfaces. In this paper we calculate high-quality reference spectra for a series of molecules of the form CH n OH m . Specifically, we looked at the neutral, charged, and excited charged forms of CH 3 OH, CH 3 O, CH 3 OH 2 , CH 2 O, CH 2 OH, CHO, and HCOH. These calculations were done using scaled MP2(full)/ 6-31g*, scaled B3LYP/6-31g*, scaled QCIST/6-31g*, and scaled MP2/6-311+G(2d,p) level. The result is a consistent set of reference spectra for a series of molecules of current interest.
We show that the DCSD (distinguishable clusters with all singles and doubles) correlation method permits the calculation of vibrational spectra at near-CCSD(T) quality but at no more than CCSD cost, and with comparatively inexpensive analytical gradients. For systems dominated by a single reference configuration, even MP2.5 is a viable alternative, at MP3 cost. MP2.5 performance for vibrational frequencies is comparable to double hybrids such as DSD-PBEP86-D3BJ, but without resorting to empirical parameters. DCSD is also quite suitable for computing zero-point vibrational energies in computational thermochemistry.
The low-frequency (terahertz) dynamics of condensed phase materials provide valuable insight into numerous bulk phenomena. However, the assignment and interpretation of experimental results requires computational methods due to the complex mode-types that depend on weak intermolecular forces. Solid-state density functional theory has been used in this regard with great success, yet the selection of specific computational parameters, namely the chosen basis set and density functional, has a profound influence on the accuracy of predicted spectra. In this work, the role of these two parameters is investigated in a series of organic molecular crystals, in order to assess the ability of various methods to reproduce intermolecular forces, and subsequently experimental terahertz spectra. Specifically, naphthalene, oxalic acid, and thymine were chosen based on the varied intermolecular interactions present in each material. The results highlight that unconstrained geometry optimizations ca...
Semiempirical calculations of molecular vibrational frequencies: The MNDO method
Journal of Molecular Structure, 1978
In recent years the value of calculating molecular force fields from semiempirical molecular orbital theory has become increasingly apparent. Thus in our own laboratories we have studied numerous chemical reactions using both the highly successful MINDO/3 [l] method and more recently the newly developed MNDO [2] procedure based on Pople and Beveridge's NDDO [3] approximation, In such studies (regardless of the particular MO method used) it is essential to demonstrate that the force constant matrix of a putative ~si~on state has a single negative eigenvalue co~~sponding to a vibrational motion coinciding with a small but fiite segment of the reaction path connecting reactant, transition state and product [4]. These statements apply even more forcefully if symmetry constraints have been imposed. Thus work in these [5] and other [4,6] laboratories has revealed numerous cases of apparently bona fide transition states (i.e. species representing energy maxima between reactants and products) which nevertheless failed to satisfy this criterion and are therefore not genuine position states, The force constant matrix is also useful for characterising minima. Stationary points which are not true minima may be obtained if unwarranted symmetry is imposed during the geometry optimisation. This occurred in our recent study of the boron hydrides [ 2b] _ Thus we now routinely calculate the force constant matrices of all calculated species for which there is any chance of error, It is therefore natural to ask with what accuracy the theoretical force fields reproduce the molecular vibrational frequencies when these are known. We have previously presented such a comprehensive analysis for 34 molecules calculated in the MINDO/$ approximation in which we demonstrated that the average error was about 10% [ 7 3. Moreover, many of the errors were systematic, similar deviations occurring for a given type of vibration in different molecules. As a bonus we also found that these fre-