CORE CORRELATION AND THE BINDING-ENERGY OF SC2

The dissociation energy of the Sc2 dimer has been computed using a multireference CI treatment and including the effects of core (3p) correlation. Special emphasis has been put on the contraction of the basis set to minimize atomic correlation energy loss and molecular superposition errors. Core (3p) correlation gives a contraction of the 4s orbital resulting in a reduced ratio between the radial extents of the 4s and 3d orbitals. This results in a decreased bond distance (by 0.20 a0) and improved 3d-3d overlap. The binding energy is increased by 0.11 eV through core correlation. The finally obtained D(e) is 0.77 eV (1.1 +/- 0.2 eV expt.) An extension of the core-polarization potential formalism to include field-gradients and quadrupole core polarizabilities is presented and compared with the results of explicit core correlation for both the atom and Sc2.