BIORTHOGONAL VALENCE BOND DESCRIPTIONS OF ELECTRONIC-STRUCTURE

A valence bond approach based on nonorthogonal orbitals in a biorthogonal representation is presented. While the scheme suffers from the lack of a variational bound on the energy functional, it is shown that with a suitable optimization of the orbitals reliable molecular wavefunctions can be obtained. A review of the background theory is given emphasizing the similarity of this approach to the familiar spin-free unitary group formulation of quantum chemistry. The details of the computer implementation are discussed and the method is illustrated with model calculations on HF, H2O and F2O2.