A modified pseudopotential approach to the heavy-atomic molecular systems: Application to the X 2Σ1/2+, A 2Π1/2, and the A 2Π3/2 states of the HgH molecule

Abstract

A new approach to the problem of quantitatively describing interactions in heavy‐atomic molecular systems is presented. In this approach the core electrons are removed from the Hamiltonian by using the exact numerical relativistic Hartree–Fock core potential. Both the local and nonlocal terms of this potential are represented in terms of a given basis set suitable to the valence electrons. Two categories of core‐orthogonality constraints are distinguished: those pertaining to outer core orbitals which can be qualitatively described by the given basis set and those pertaining to the inner core orbitals which cannot be thus described. While explicit descriptions for the former are used as orthogonality constraints, approximate ’’pseudopotential’’‐type terms are introduced into the Fock operators to represent the latter’s orthogonality effects. Estimates of the core distortion and relativistic contributions are considered. Application to the lowest ²Σ_1/2⁺, ²Π_1/2, and ²Π_3/2 states of the HgH molecule is described.