Accurate effective core potential for germanium. Application to the singlet-triplet splitting in GeH₂

Abstract

An accurate effective core potential (ECP), including frozen 3s, 3p orbitals and a single-zeta contracted 3d orbital, has been developed for germanium. The ECP with associated valence basis set reproduces the corresponding all-electron results for the atomic excitations and the geometry and excitation energies of GeH2. At the SCF, CAS SCF and CI levels the maximum difference from the all-electron results is 0.5 kcal/mol in the 1A1-3B1 excitation energy. Finally, the ECP description is used with an extended valence basis set and large-scale CAS SCF and multi-reference CI wavefunctions to compute the singlet-triplet separation; the final CI result including the Davidson correction is 22.5 kcal/mol. © 1986.