  The generalized Heitler-London (GHL) theory provides a straightforward way to
express the potential energy surface of H_3 in terms of Coulomb and exchange
energies which can be calculated either by perturbation theory or using the
surface integral method (SIM). By applying the Rayleigh-Schroedinger
perturbation theory, GHL theory for the quartet spin state of H_3 is shown to
yield results equivalent to the symmetrized Rayleigh-Schroedinger version of
symmetry adapted perturbation theory (SAPT). This equivalence allows a
comparison with the corresponding results obtained by the surface integral
method. The surface integral result calculated with a product of atomic wave
functions is found to have certain advantages over the perturbation approach.
