94 research outputs found
Assessment of Various Density Functionals and Basis Sets for the Calculation of Molecular Anharmonic Force Fields
In a previous contribution (Mol. Phys. {\bf 103}, xxxx, 2005), we established
the suitability of density functional theory (DFT) for the calculation of
molecular anharmonic force fields. In the present work, we have assessed a wide
variety of basis sets and exchange-correlation functionals for harmonic and
fundamental frequencies, equilibrium and ground-state rotational constants, and
thermodynamic functions beyond the RRHO (rigid rotor-harmonic oscillator)
approximation. The fairly good performance of double-zeta plus polarization
basis sets for frequencies results from an error compensation between basis set
incompleteness and the intrinsic error of exchange-correlation functionals.
Triple-zeta plus polarization basis sets are recommended, with an additional
high-exponent function on second-row atoms. All conventional hybrid GGA
functionals perform about equally well: high-exchange hybrid GGA and meta-GGA
functionals designed for kinetics yield poor results, with the exception of of
the very recently developed BMK functional which takes a middle position along
with the HCTH/407 (second generation GGA) and TPSS (meta-GGA) functionals. MP2
performs similarly to these functionals but is inferior to hybrid GGAs such as
B3LYP and B97-1.Comment: Int. J. Quantum Chem., in press (special issue on vibrational
spectroscopies
Anharmonic force fields of perchloric acid, HClO, and perchloric anhydride, ClO. An extreme case of inner polarization
DFT (density functional theory) anharmonic force fields with basis sets near
the Kohn-Sham limit have been obtained for perchloric acid, HClO, and
perchloric anhydride, ClO. Calculated fundamental frequencies are in
very good agreement with available experimental data. Some reassignments in the
vibrational spectra of ClO are proposed based on our calculations.
HClO and ClO are particularly severe examples of the `inner
polarization' phenomenon. The polarization consistent basis sets pc-1 and pc-2
(as well as their augmented counterparts) should be supplemented with two
(preferably three) and one (preferably two) high-exponent functions,
respectively, on second-row atoms. Complete anharmonic force fields are
available as electronic supporting information.Comment: J. Mol. Struct., in press (special issue); Electronic Supporting
Information at http://theochem.weizmann.ac.il/web/papers/Cl2O7.htm
Advantages and drawbacks of quantum mechanical static and dynamic approaches to modelling infrared spectra
cited By 2International audienceWe present quantum mechanical vibrational computations beyond the harmonic approximation from effective second order perturbative and variation perturbation treatments defined as static approaches, as well as vibrational analysis from density functional theory molecular dynamics trajectories at 300 and 600 K. The four schemes are compared in terms of prediction of fundamental transitions, and simulation of the corresponding medium infrared spectrum at the same level of theory using the B3LYP/6-31+G(d,p) description of the electronic structure. We summarize conclusions about advantages and drawbacks of these two approaches and report the main results obtained for semi-rigid and flexible molecules. © 2009 Chinese Physical Society
Computational aspects of the modelling of vibrational properties of gases, liquids and solids
cited By 0International audienceno abstrac
Vibrational treatment from a variation-perturbation scheme: The VCI-P method. Application to the glycolaldehyde
cited By 0International audienceAn iterative variation-perturbation algorithm allowing a anharmonic vibrational treatment of polyatomic molecules is proposed. This state specific process consists on an iterative construction of small 3N-5 Vibrational Configuration Interation (VCI) matrixes (N being the number of atoms) with the most pertinent couplings and includes a perturbative treatment of the weakest contributions. Thus, this scheme allow to massively reduce the size of the CI matrixes with a minimum loss of correlation energy. Through the example of H2CO, the results stemmed from the VCI-P process are compared to their full VCI counterpart. Moreover, the computations of anharmonic intensities are also implemented. As illustration, the modelization of the medium infrared (MIR) spectrum of the glycolaldehyde is reported. © 2012 American Institute of Physics
Time-independent and time-dependent methods for the calculation of the vibrational spectra: H2CN as example
cited By 3International audienceComputed anharmonic transitions and intensities of H2CN are reported in a spectral range ranging from 900 to 2,900 cm-1. Four vibrational treatments were considered from a. B3LYP/6-31+G(d,p) potential electronic surface: The second, order perturbational method, the full configuration interaction, the discrete variable representation method and the vibrational analysis arising from a molecular dynamics trajectory. The four approaches yield basically the same results since the convergence of the values is achieved by about 15-20 cm-1. © 2009 Wiley Periodicals, Inc
- …