Four-component relativistic configuration-interaction calculation using the reduced frozen-core approximation

The reduced frozen-core approximation (RFCA) is a kind of frozen-core approximation (FCA). In our previous study [J. Chem. Phys. 109, 8182 (1998)], we found that Dirac-Fock-Roothaan calculations using RFCA had some desirable features compared to the all-electron and usual FCA calculations. In this study, in addition to these features, we found that they also describe well unoccupied as well as occupied orbitals. We developed a fully relativistic multireference configuration-interaction (CI) program that incorporates these features of RFCA, and report CI calculations for ThO and AuH. The calculated spectroscopic constants agree well with experimental values. (C) 2002 American Institute of Physics.