Spin-orbit effects calculated by a configuration interaction method using determinants of two-component molecular spinors: Test calculations on Rn and T1H

We are developing a relativistic configuration interaction (RCI) method for polyatomic molecules using relativistic effective core potentials (REP). The present RCI method incorporates spin-orbit interactions from the HF step through the use of two-component molecular spinors confirming Kramers' degeneracy. Test calculations for the low-lying excited states of the Rn atom and the ground state of T1H demonstrate that the present RCI method has some advantages over the conventional RCI methods using the same REP but introducing spin-orbit terms only at the CI steps.