OPTIMALLY CONVERGENT DETERMINANTAL EXPANSION OF MANY-ELECTRON WAVE-FUNCTIONS

It is shown that the many-electron wave function can be expanded optim ally in terms of a set of Slater determinants that reduces considerabl y the number of determinants differing by a single-particle wave funct ion. The method is based on a variational procedure. The first step of the present method is the Brueckner optimization. The other determina nts of the expansion are obtained by successive optimizations performe d under additional constraints. The method is illustrated by consideri ng specifically three- and four-particle examples. Finally, it is conc luded that the eigenstates of a many-particle system can be approximat ed by states that neglect single-particle excitations. The zero-order approximation of the present scheme is the Hartree-Fock approximation.