Soft Coulomb hole method applied to theoretical equilibrium geometries of singlet diatomic molecules

Abstract

It has been demonstrated that the soft Coulomb hole method is a reliable and efficient approach to calculate the electron correlation energy for atoms and molecules. In this method the perturbation operator −e−ωr122/r12 is introduced, where ω determines the size of the Coulomb hole. The set of parameters for ω has been redetermined to calculate equilibrium bond distances. Calculations have been performed for 41 homo- and heteronuclear singlet diatomic molecules and ions (X 1Σ+), including atoms of the second and third periods of the periodic table. The soft Coulomb hole correlation energies are compared to the corresponding empirical correlation energies. In general, calculated equilibrium bond distances are in better agreement with the experimental values than Hartree-Fock and Mo/ller-Plesset-2 results. With respect to Mo/ller-Plesset-3, the soft Coulomb hole method gives slightly larger values for the average deviations, except for the homonuclear series.

Explicitly correlated SCF study of anharmonic vibrations in (H2O)2

“…The CSCF method [9] depends on the two-electron integral derived by Otto et al [10] and Hernandez-Laguna et al [11] for Gaussian lobe basis (GLO) sets. In both the GLO treatment by Otto et al and the previous Slater basis treatment of atoms by Chakravorty and Clementi [12], the w exponent was based on a formula in terms of orbital angular momentum with up to 12 parameters and this is a limitation for low-symmetry molecules.…”

Soft Coulomb hole method applied to molecules

“…It may be interpreted as an effective potential, introducing a screening of the Coulomb potential. A more detailed explanation can be found elsewhere 21, 22.…”

“…All parameters are listed, for atoms 17, in the second column of Table I. Expressions for Coulomb and exchange SCH integrals can be found elsewhere 17, 21, 22.…”

“… b Average of the absolute differences between empirical 1, 2 and SCH correlation energies (au) of 10 diatomic molecules 22. …”

“…The two‐electron SCH integrals were resolved for molecules, and a new parametrization of the size of the hole was proposed for molecules. Later, Hernández‐Laguna et al 22 determined new parameters for the molecular SCH method (MSCH) especially adapted for bond lengths, by means of fitting to a reference set of diatomic molecules. The method was successful in calculating bond lengths for a large set of diatomic molecules.…”