The Kramers’ restricted complete active space self-consistent-field method for two-component molecular spinors and relativistic effective core potentials including spin–orbit interactions

Abstract

The Kramers’ restricted complete active space self-consistent-field (KR-CASSCF) method based upon two-component molecular spinors and relativistic effective core potentials including spin–orbit interactions is implemented, employing the two-step approach, in which the expansion coefficients of configurations and molecular spinors are determined alternately. The present approach allows the influence of spin–orbit interactions to be taken into account in the optimization of one-electron wave function space. Test calculations were performed for the Hg atom, Au− anion, and Tl+ cation with the closed-shell electronic configuration, the ground state potential energy curves of homo-nuclear diatomic molecules, As2, Sb2, and Bi2, over a wide range of inter-nuclear distances, and the bond fission of a polyatomic molecule CH3I. The results show that the KR-CASSCF method properly describes the dissociation of molecules for the fine-structure states. It is also evident that molecular properties are affected by optimized spinors for systems containing heavy atoms such as Bi2 and CH3I at the CASSCF level of theory.