A VARIATIONAL BIORTHOGONAL VALENCE-BOND METHOD

The details of a simple and efficient scheme for performing variationa l biorthogonal valence bond calculations are presented. A variational bound on the energy functional is obtained through the use of a comple te configuration expansion in a well-chosen subset of orbitals. The re sultant wave functions are clearly dominated by the covalent (spin-cou pled) structures, with a negligible contribution from ionic structures . The orbitals obtained compare favorably with overlap enhanced atomic orbitals obtained by other valence bond approaches. The method is ill ustrated by calculations on water and dioxygen difluoride. (C) 1994 by John Wiley and Sons, Inc.