Convergence enhancement in the iterative solution of the second-order contracted Schrodinger equation

The iterative solution of the contracted Schrodinger equation is coupled with a second-order reduced density matrix purification procedure, which corrects its N- and S-representability defects, and with a regulating convergence device. An analysis of the effects of these new implementations is reported. The method is applied to the calculation of the potential energy curves of the BeH2 and Li-2 molecules. The results compare very closely with those of the full configurations interaction. (c) 2005 Wiley Periodicals, Inc.