Ab initio calculations for the potential curves and spin-orbit coupling of Mg2

The ground state and several low-lying excited states of the Mg-2 dimer have been studied by means of a combination of the complete-active-space multiconfiguration self-consistent-field (CASSCF)/CAS multireference second-order perturbation theory (CASPT2) method and coupled-cluster with single and double excitations and perturbative contribution of connected triple excitations [CCSD(T)] scheme. Reasonably good agreement with experiment has been obtained for the CCSD(T) ground-state potential curve but the dissociation energy of the only experiinentally known A (1)Sigma(u)(+) excited state of Mg2 is somewhat overestimated at the CASSCF/CASPT2 level. The spectroscopic constants D-e, R-e and omega(e) deduced from the calculated potential curves for other states are also reported. In addition, some spin-orbit matrix elements between the excited singlet and triplet states of Mg-2 have been evaluated as a function of internuclear separation.