We present a general method for extracting the internal space of an ar
bitrary wave function, exploiting the molecular symmetry. This permits
the rewriting of a wave function built with nonorthogonal orbitals as
a compact expansion of Slater determinants over orthogonal orbitals.
The method is applied to valence bond (VB) and projected unrestricted
Hartree-Fock (PUHF) functions along the potential curves of some diato
mics, namely He-2(+), F-2(-), and F-2. These functions are then used a
s references for further configuration interaction and perturbative Mo
ller-Plesset calculations. (C) 1998 American Institute of Physics.