Valence-only molecular calculations with a non-empirical pseudopotential method

Abstract

Two model potentials are proposed for effective core potentials which enable the molecular electronic structure to be described in terms of valence-only electrons. These pseudopotential operators consist of a coulomb local potential and two sets of projection operators simulating the non-local potential and preventing the collapse of the valence orbitals into the inner cores; they are angular momentum dependent. The parameters entering in their definition are determined on purely theoretical grounds from neutral atom SCF calculations. These parameters turn out to be completely independent of the valence description. The two models are presented for atoms up to chlorine and tested on some hydride and non-hydride molecules using a minimal basis set of Slater orbitals and computing molecular energy levels, minimum geometries, dipole moments and force constants. The results are compared with those of the corresponding all-electron calculations, the agreement obtained being to a few per cent or better for all the computed quantities.