Three-electron approach of HgH using relativistic effective core,core polarization and spin-orbit operators: the low-lying states

The lowest states of HgH are calculated using a non-empirical relativistic effective core potential considering the mercury atom as a two-electron system. The configuration interaction is done within the CIPSI algorithm. Core-valence polarization and correlation energy are included through a perturbation treatment. The spin-orbit coupling is introduced through an effective hamiltonian in a basis of LS states. Results obtained for the lowest states of HgH are in fair accordance with experimental results. The “atom in molecule” approximation for SO coupling is discussed.