Valence ab initio calculation of the potential energy curves for the Sr2 dimer

The ground and excited states of the Sr2 molecule has been investigated by use of a two-valence-electron semi-empirical pseudopotential (PP(2)) and applying the internally contracted multireference CI method (ICMRCI) and complete active space SCF (CAS SCF) reference wavefunctions. In the calculations, core polarization and core-valence correlation have been accounted for by adding a core-polarization potential (CPP) to the hamiltonian. Moreover, the single-reference coupled-cluster approach with single and double excitations including a perturbative treatment of triple excitations (CCSD(T)) has been used in ground-state calculations for Sr2 and Sr2+ to yield more accurate potential curves. Spin–orbit (SO) coupling between the singlet and triplet states correlating, respectively, with the (5p)1P and (5p)3P Sr terms has been investigated using a semi-empirical two-electron SO pseudopotential.