The half-projected Hartree-Fock method: some new aspects

Abstract

The half-projected Hartree-Fock (HPHF) theory set forth by Smeyers (An. Fis., 67 (1971) 17) is extended in order to obtain all the necessary expressions for the calculations of the first and second derivatives of the energy functional. This permits the implementation of well known direct optimization techniques in the framework of the HPHF method. We also propose a treatment of linear response properties based on a HPHF reference function and derive the equation defining the Tamm-Dankoff (monoexcited CI) approximation.