A GENERALIZED HYLLERAAS CORRELATIVE FACTOR IN VARIATIONAL CALCULATION

A generalized Hylleraas type of correlative factor which includes the l not equal 0 partial waves of relative motion of each pair of particl es is introduced in variational calculations of few-body systems. As a n example, the ground state and the first doubly excited S-l(e) state of the helium atom are obtained simultaneously from a diagonalization of the Hamiltonian in an 11-dimensional model space spanned by basis f unctions with or without the generalized Hylleraas factor. It was foun d that this factor can in general improve the eigenenergies; in partic ular, it affects explicitly the structure of the wavefunction of the e xcited state.