ON THE DAMPED MULTIPOLE EXPANSION OF THE INDUCTION ENERGY IN H2+

Following early work by Kutzelnigg on the correlation cusp, we have at tempted to improve convergence of the damped multipole expansion of th e second-order induction energy for H-2+ by including a separately det ermined cusp correction of the form phi = f (r(B))psi0 into the first- order function in order to avoid divergency at the proton position whe n r(B) = 0. Three different cusp wavefunctions, all derived from the T aylor expansion of f (r(B)) into positive powers of r(B) have been exa mined, and the best compromise between simplicity and accuracy is foun d for the function phi = -r(B)psi0. Few residual multipoles, variation ally approximated in terms of one-centre linear pseudostates, are then found necessary to reproduce accurately the induction energy at the d istance of the chemical bond.