IS ANTISYMMETRIZATION NECESSARY

We demonstrate that there exists a class of primitive wavefunctions which may be used to calculate the energy and some other properties of electronic systems without first having to form the antisymmetric projection of the functions. The primitive functions G are solutions to a nonlinear equation which depends on the hamiltonian and on three other operators. The latter three may be chosen with considerable freedom. We propose a choice of these operators which, on the basis of formal and numerical evidence, yield G's which are well approximated in zero order by a product of atomic, molecular or other electronic group functions. We use the proposed choice of operators to formulate a new exchange perturbation theory and explain why this theory is simpler to apply than a theory which explicitly uses the antisymmetrizer. We consider, also, some general implications of our results. © 1979.