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

It has been demonstrated that the soft Coulomb hole method is a reliable an d efficient approach to calculate the electron correlation energy for atoms and molecules. In this method the perturbation operator -e(-wr2)12/r(12) i s introduced, where omega determines the size of the Coulomb hole. The set of parameters for omega has been redetermined to calculate equilibrium bond distances. Calculations have been performed for 41 homo- and heteronuclear singlet diatomic molecules and ions (X (1)Sigma(+)), including atoms of th e second and third periods of the periodic table. The soft Coulomb hole cor relation energies are compared to the corresponding empirical correlation e nergies. In general, calculated equilibrium bond distances are in better ag reement with the experimental values than Hartree-Fock and Moller-Plesset-2 results. With respect to Moller-Plesset-3, the soft Coulomb hole method gi ves slightly larger values for the average deviations, except for the homon uclear series. (C) 1999 American Institute of Physics. [S0021-9606(99)30214 -2].