AB-INITIO MOLECULAR-ORBITAL CALCULATIONS BY THE RESONATING HARTREE-FOCK APPROACH - SUPERPOSITION OF NONORTHOGONAL SLATER DETERMINANTS

The resonating Hartree-Fock (ResHF) method is applied to ab initio MO calculations of CO, This method approximates correlated wavefunctions by superposition of non-orthogonal Slater determinants, where both the CI coefficients and the orbitals in the determinants are variationall y determined. The ResHF, with two or three generating determinants, ex plains the correlation energy to the same extent as the full-valence C ASSCF wavefunction with 328 CSFs. Furthermore, the method reproduces t he dipole moment more accurately, reflecting a better long-range behav ior of the wavefunction. This implies the ResHF method provides more s uitable reference functions in multireference methods.