The a b i n i t i o model potential method. Second series transition metal elements

The ab initio core method potential model (AIMP) has already been presented in its nonrelativistic version and applied to the main group and first series transition metal elements [J. Chem. Phys. 86, 2132 (1987); 91, 7011 (1989)]. In this paper we extend the AIMP method to include relativistic effects within the Cowan–Griffin approximation and we present relativistic Zn-like core model potentials and valence basis sets, as well as their nonrelativistic Zn-like core and Kr-like core counterparts. The pilot molecular calculations on YO, TcO, AgO, and AgH reveal that the 4p orbital is indeed a core orbital only at the end part of the series, whereas the 4s orbital can be safely frozen from Y to Cd. The all-electron and model potential results agree in 0.01–0.02 Å in Re and 25–50 cm−1 in ν̄e if the same type of valence part of the basis set is used. The comparison of the relativistic results on AgH with those of the all-electron Dirac–Fock calculations by Lee and McLean is satisfactory: the absolute value of Re is reproduced within the 0.01 Å margin and the relativistic contraction of 0.077 Å is also very well reproduced (0.075 Å). Finally, the relative magnitude of the effects of the core orbital change, mass–velocity potential, and Darwin potential on the net relativistic effects are analyzed in the four molecules studied.