Precise ab initio calculations of the 3d transition-metal clusters: Sc2

The ground ${}^5\Sigma _u^ -$5Σu− state of Sc2 was studied by the valence multireference configuration interaction method with single and double excitations plus Davidson correction (MRCISD(+Q)) at the complete basis set limit. The calculations were made under C2v symmetry restrictions, which allowed us to obtain at the dissociation limit the Sc atoms in different states (in all previous studies of Sc2 the D2h symmetry group was employed). From the Mulliken population analysis and energy calculations follows that in the ground state Sc2 dissociates in one Sc in the ground state and the other in the second excited quartet state, 4Fu. The corrected parameters of the ground potential curve are the following: Re = 5.2 bohr, De = 50.37 kcal/mol, and ωe = 234.5 cm-1. The dissociation energy in respect to the dissociation on two Sc in the ground states was estimated as De = 9.98 kcal/mol.