27 research outputs found
Double hybrid density-functional theory using the Coulomb-attenuating method
A double hybrid approximation using the Coulomb-attenuating method (CAM-DH)
is derived within range-separated density-functional perturbation theory, in
the spirit of a recent work by Cornaton {\it et al.} [Phys. Rev. A 88, 022516
(2013)]. The energy expression recovered through second order is linear in the
parameters and that control the Coulomb attenuation. The
method has been tested within the local density approximation on a small test
set consisting of rare-gas and alkaline-earth-metal dimers as well as diatomics
with single, double and triple bonds. In this context, the semi-empirical
and parameters, that were optimized for the hybrid
CAM-B3LYP functional, do not provide accurate interaction and total energies.
Using semi-local functionals with density scaling, that was neglected in this
work, may lead to different conclusions. Calibration studies on a larger test
set would be necessary at this point. This is left for future work. Finally, we
propose as a perspective an alternative CAM-DH approach that relies on the
perturbation expansion of a partially long-range interacting wavefunction. In
this case the energy is not linear anymore in and . Work is in
progress in this direction.Comment: 36 pages, 6 figure
Alternative separation of exchange and correlation energies in range-separated density-functional perturbation theory
An alternative separation of short-range exchange and correlation energies is
used in the framework of second-order range-separated density-functional
perturbation theory. This alternative separation was initially proposed by
Toulouse et al. [Theor. Chem. Acc. 114, 305 (2005)] and relies on a long-range
interacting wavefunction instead of the non-interacting Kohn-Sham one. When
second-order corrections to the density are neglected, the energy expression
reduces to a range-separated double-hybrid (RSDH) type of functional, RSDHf,
where "f" stands for "full-range integrals" as the regular full-range
interaction appears explicitly in the energy expression when expanded in
perturbation theory. In contrast to usual RSDH functionals, RSDHf describes the
coupling between long- and short-range correlations as an orbital-dependent
contribution. Calculations on the first four noble-gas dimers show that this
coupling has a significant effect on the potential energy curves in the
equilibrium region, improving the accuracy of binding energies and equilibrium
bond distances when second-order perturbation theory is appropriate.Comment: 5 figure
Complete analytic anharmonic hyper-Raman scattering spectra
We present the first computational treatment of the complete second-order vibrational perturbation
theory applied to hyper-Raman scattering spectroscopy. The required molecular properties are
calculated in a fully analytic manner using a recently developed program [Ringholm, Jonsson and
Ruud, J. Comp. Chem., 2014, 35, 622] that utilizes recursive routines. For some of the properties,
these calculations are the first analytic calculations of their kind at their respective levels of theory.
We apply this approach to the calculation of the hyper-Raman spectra of methane, ethane and
ethylene and compare these to available experimental data. We show that the anharmonic
corrections have a larger effect on the vibrational frequencies than on the spectral intensities, but
that the inclusion of combination and overtone bands in the anharmonic treatment can improve the
agreement with the experimental data, although the quality of available experimental data limits a
detailed comparison
Temperature dependence of the static permittivity andintegral formula for the Kirkwood correlation factor ofsimple polar fluids
An exact integral formula for the Kirkwood correlation factor of isotropic
polar fluids is derived from the equilibrium averaged rotational Dean
equation, which as compared to previous approaches easily lends itself to
further approximations. The static linear permittivity of polar fluids
is calculated as a function of temperature, density and molecular
dipole moment in vacuo for arbitrary pair interaction potentials. Then, using
the Kirkwood superposition approximation for the three-body orientational
distribution function, we suggest a simple way to construct model potentials of
mean torques considering permanent and induced dipole moments. We successfully
compare the theory with the experimental temperature dependence of the static
linear permittivity of various polar fluids such as a series of linear
monohydroxy alcohols, water, tributyl phosphate, acetonitrile, acetone,
nitrobenzene and dimethyl sulfoxide, by fitting only one single parameter,
which describes the induction to dipole-dipole energy strength ratio. We
demonstrate that comparing the value of with unity in order to deduce the
alignment state of permanent dipole pairs, as is currently done is in many
situations, is a misleading oversimplification, while the correct alignment
state is revealed when considering the proper interaction potential. Moreover
we show, that picturing H-bonding polar fluids as polar molecules with
permanent and induced dipole moments without invoking any specific H-bonding
mechanism is in many cases sufficient to explain experimental data of the
static dielectric constant. In this light, the failure of the theory to
describe the experimental temperature dependence of the static dielectric
constant of glycerol, a non-rigid polyalcohol, is not due to the lack of
specific H-bonding mechanisms, but rather to an oversimplified model potential
for that particular molecule
Quantum study of strong and weak interactions : development of double-hybrid functionals and of analytic potential surfaces
Les travaux réalisés au cours de cette thèse se décomposent en deux thèmes principaux, eux-même subdivisés enplusieurs projets. D'une part, des travaux ont été menés concernant l'analyse et le développement de fonctionnelles « doubles hybrides ». Une analyse des fonctionnelles « doubles hybrides » à séparation linéaire le long de la connexionadiabatique a été proposée. Une nouvelle fonctionnelle « double hybride » à séparation de portée basée sur uneséparation alternative de l'énergie d'échange et de corrélation, RSDHf, a été développée. D'autre part, des travaux quant au développement de surfaces d'énergie potentielle (SEP) analytiques ont été menés. Un nouveau potentiel analytique a été proposé pour la description de la SEP des systèmes triatomiques. La combinaison de ce potentiel avec un potentiel électrostatique a été utilisé pour le développement de SEP analytiques pour de petits systèmes en interaction faible : H2O···HF, HF2-, Ne···ClF.Works done during this thesis split into two main themes, themselves subdivided in several projects. On the one hand, works have been led concerning the analysis and the development of double-hybrid functionals. An analysis of linearly-separated double-hybrid functionals along the adiabatic connection has been proposed. A new range-separated double-hybrid functional based on an alternative separation of the exchange-correlation energy, RSDHf, has been developed. On the other hand, works related to the development of analytic potential energy surfaces (PES) has been led. A new analytic potential has been proposed for the description of the PES of triatomic systems. The combinaition of this potential with an electrostatic potential has been used for the development of analytic PES for small systems in weak interaction : H2O···HF, HF2-, Ne···ClF
Etude quantique des liaisons fortes et faibles : développement de fonctionnelles "doubles-hybrides" et de surfaces de potentiel analytiques
Works done during this thesis split into two main themes, themselves subdivided in several projects. On the one hand, works have been led concerning the analysis and the development of double-hybrid functionals. An analysis of linearly-separated double-hybrid functionals along the adiabatic connection has been proposed. A new range-separated double-hybrid functional based on an alternative separation of the exchange-correlation energy, RSDHf, has been developed. On the other hand, works related to the development of analytic potential energy surfaces (PES) has been led. A new analytic potential has been proposed for the description of the PES of triatomic systems. The combinaition of this potential with an electrostatic potential has been used for the development of analytic PES for small systems in weak interaction : H2O···HF, HF2-, Ne···ClF.Les travaux réalisés au cours de cette thèse se décomposent en deux thèmes principaux, eux-même subdivisés enplusieurs projets. D'une part, des travaux ont été menés concernant l'analyse et le développement de fonctionnelles « doubles hybrides ». Une analyse des fonctionnelles « doubles hybrides » à séparation linéaire le long de la connexionadiabatique a été proposée. Une nouvelle fonctionnelle « double hybride » à séparation de portée basée sur uneséparation alternative de l'énergie d'échange et de corrélation, RSDHf, a été développée. D'autre part, des travaux quant au développement de surfaces d'énergie potentielle (SEP) analytiques ont été menés. Un nouveau potentiel analytique a été proposé pour la description de la SEP des systèmes triatomiques. La combinaison de ce potentiel avec un potentiel électrostatique a été utilisé pour le développement de SEP analytiques pour de petits systèmes en interaction faible : H2O···HF, HF2-, Ne···ClF
Benchmarking fully analytic DFT force fields for vibrational spectroscopy: A study on halogenated compounds
This work presents an investigation of the theoretical predictions yielded by anharmonic force fields having the cubic and quartic force constants are computed analytically by means of density functional theory (DFT) using the recursive scheme developed by M. Ringholm et al. (J. Comput. Chem. 35 (2014) 622). Different functionals (namely B3LYP, PBE, PBE0 and PW86x) and basis sets were used for calculating the anharmonic vibrational spectra of two halomethanes. The benchmark analysis carried out demonstrates the reliability and overall good performances offered by hybrid approaches, where the harmonic data obtained at the coupled cluster with single and double excitations level of theory augmented by a perturbational estimate of the effects of connected triple excitations, CCSD(T), are combined with the fully analytic higher order force constants yielded by DFT functionals. These methods lead to reliable and computationally affordable calculations of anharmonic vibrational spectra with an accuracy comparable to that yielded by hybrid force fields having the anharmonic force fields computed at second order Møller-Plesset perturbation theory (MP2) level of theory using numerical differentiation but without the corresponding potential issues related to computational costs and numerical errors