  We study a new approach to determine the asymptotic behaviour of quantum
many-particle systems near coalescence points of particles which interact via
singular Coulomb potentials. This problem is of fundamental interest in
electronic structure theory in order to establish accurate and efficient models
for numerical simulations. Within our approach, coalescence points of particles
are treated as embedded geometric singularities in the configuration space of
electrons. Based on a general singular pseudo-differential calculus, we provide
a recursive scheme for the calculation of the parametrix and corresponding
Green operator of a nonrelativistic Hamiltonian. In our singular calculus, the
Green operator encodes all the asymptotic information of the eigenfunctions.
Explicit calculations and an asymptotic representation for the Green operator
of the hydrogen atom and isoelectronic ions are presented.
