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This work reports an efficient density‐fitting implementation of the density‐based basis‐set correction (DBBSC) method in the MOLPRO software. This method consists in correcting the energy calculated by a wave‐function method with a given basis set by an adapted basis‐set correction density functional incorporating the short‐range electron correlation effects missing in the basis set, resulting in an accelerated convergence to the complete‐basis‐set limit. Different basis‐set correction density‐functional approximations are explored and the complementary‐auxiliary‐basis‐set single‐excitation correction is added. The method is tested on a benchmark set of reaction energies at the second‐order Møller–Plesset (MP2) level and a comparison with the explicitly correlated MP2‐F12 method is provided. The results show that the DBBSC method greatly accelerates the basis convergence of MP2 reaction energies, without reaching the accuracy of the MP2‐F12 method but with a lower computational cost. [ABSTRACT FROM AUTHOR]

We construct the complementary short‐range correlation relativistic local‐density‐approximation functional to be used in relativistic range‐separated density‐functional theory based on a Dirac‐Coulomb Hamiltonian in the no‐pair approximation. For this, we perform relativistic random‐phase‐approximation calculations of the correlation energy of the relativistic homogeneous electron gas with a modified electron–electron interaction, we study the high‐density behavior, and fit the results to a parametrized expression. The obtained functional should eventually be useful for electronic‐structure calculations of strongly correlated systems containing heavy elements. [ABSTRACT FROM AUTHOR]

The computation of high-harmonic generation spectra by means of Gaussian basis sets in approaches propagating the time-dependent Schrödinger equation was explored. The efficiency of Gaussian functions specifically designed for the description of the continuum proposed by Kaufmann et al. (J Phys B 1989, 22, 2223) was investigated. The range of applicability of this approach was assessed by studying the hydrogen atom, that is, the simplest atom for which 'exact' calculations on a grid could be performed. The effect of increasing the basis set cardinal number, the number of diffuse basis functions, and the number of Gaussian pseudo-continuum basis functions for various laser parameters was notably studied. The results showed that the latter significantly improved the description of the low-lying continuum states, and provided a satisfactory agreement with grid calculations for laser wavelengths λ0 = 800 and 1064 nm. The Kaufmann continuum functions, therefore, appeared as a promising way of constructing Gaussian basis sets for studying molecular electron dynamics in strong laser fields using time-dependent quantum-chemistry approaches. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Decomposition of the Coulomb electron–electron interaction into a long‐range and a short‐range part is described within the framework of density functional theory, deriving some scaling relations and the corresponding virial theorem. We study the behavior of the local density approximation in the high‐density limit for the long‐range and the short‐range functionals by carrying out a detailed analysis of the correlation energy of a uniform electron gas interacting via a long‐range‐only electron–electron repulsion. Possible definitions of exchange and correlation energy densities are discussed and clarified with some examples. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [ABSTRACT FROM AUTHOR]

We calculate the short‐range exchange‐correlation energy of the uniform electron gas with two modified electron–electron interactions. While the short‐range exchange functionals are calculated analytically, coupled‐cluster and Fermi‐hypernetted‐chain calculations are carried out for the correlation energy and the results are fitted to an analytical parametrization. These data enable us to construct the local density approximation corresponding to these modified interactions. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 [ABSTRACT FROM AUTHOR]