THE HALF-PROJECTED HARTREE-FOCK METHOD - SOME NEW ASPECTS

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 know n direct optimization techniques in the framework of the HPHF method. We also propose a treatment of linear response properties based on a H PHF reference function and derive the equation defining the Tamm-Danko ff (monoexcited CI) approximation.