Valence ab initio calculation of the potential energy curves for Ca-rare gas van der Waals molecules

Adiabatic potential curves for the ground state and several low-lying excited states of the calcium atom interacting with rare gas (RG) atoms have been obtained in the AS coupling scheme from valence ab initio complete-active-space multiconfiguration self-consistent-field (CASSCF)/complete-active-space multireference second-order perturbation theory (CASPT2) calculations. In the calculations the Ca2+ and RG(8+) atomic cores are represented by scalar-relativistic energy-consistent pseudopotentials. Core polarization and core-valence correlation have been accounted for by adding a core polarization potential (CPP) to the Hamiltonian. Moreover, the closed-shell single-reference coupled-cluster approach with single and double excitations including a perturbative treatment of triple excitations (CCSD(T)) has been used to obtain more accurate ground-state potential curves for the species. The transition dipole moments from the around state to the excited (1)Sigma and (1)Pi states correlating with the (3d)D-1 and (4p)P-1 Ca terms have been evaluated as a function of R. Fine structure of the molecular terms has also been studied using a semi-empirical two-electron spin-orbit pseudopotential for the Ca atom. (C) 2003 Published by Elsevier Science B.V.