Cg. Bao et Jn. He, A GENERALIZED HYLLERAAS CORRELATIVE FACTOR IN VARIATIONAL CALCULATION, Journal of physics. B, Atomic molecular and optical physics, 28(11), 1995, pp. 2039-2047
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.