LCAO-MO Formulation of Pseudopotential Theory

Pseudopotential Theory replaces the requirement that valence orbitals be orthogonal to core ones by an effective potential in the computation of the valence orbitals. Instead of the usual differential equation or perturbation treatments, the appropriate secular equation for the expansion of the valence molecular orbitals in a nonorthogonal atomic orbital basis is obtained. It takes the famillar form with the diagonal elements of the energy matrix significantly modified and with corrections to the overlap matrix and off-diagonal energy matrix elements that may normally be disregarded in semiempirical molecular orbital calculations.