Local spin density functional analysis of exchange and correlation effects on some first row diatomic molecules

Abstract

We have constructed an extended Hartree–Fock computational method and program which is very similar to standard quantum chemical program packages for molecular electronic structure calculations but allows exchange and/or correlation to be treated by a local approximation as an option. The local spin density functionals accounting for exchange and/or correlation can be included in the self-consistent field (SCF) iterations to examine their effect or added in the final estimation of the total energy to gain efficiency at an often marginal loss in accuracy. We report calculations for H2, HF, N2, F2, and OH− in modest basis sets to examine the effect of local approximations for exchange and/or correlation on the bond strength, bond length, and vibrational frequencies of small covalently bonded molecules. The results show a systematic pattern which can be understood in terms of the dependence of the Hartree–Fock exchange effect on the spatial extent of the canonical orbitals.