Two-body densities and effective potentials

For an A-particle quantum system in a state Psi, the movement of any pair o f particles is studied. Using the corresponding two-body densities, the eff ective potential that determines the relative and center of mass movements of the pair of particles is built. Some aspects of the proposed general pro cedure are applied to different, functions used to describe the ground stat e of the helium atom. (C) 2000 John Wiley & Sons, Inc.