A proposal for the calculation of the correlation energy using a onehyphen;center expansion in larger molecules

摘要

For an easier calculation of correlation in larger molecules (number of electronsNquest;100) a onehyphen;center expansion is proposed for the onehyphen;electron orbitals used to generate the excited configurations. The suggested procedure consists of the usual LCAO treatment at the Hartreendash;Fock level, but proposes a second (less accurate) Hartreendash;Fock calculation based on onehyphen;center basis functions for the calculation of the interconfigurational matrix elements. The advantages (including the easier control over the completeness of basis set) and disadvantages of the suggested new procedures are discussed and the possibilities of informative test calculations are pointed out.