An Anderson-Newns tight binding model obtained from the Hartree-Fock approximation of a bonding-pairs truncated many-body Hamiltonian, is used to describe the adsorption of H on sodium s-like metal. This model does not require adjustable parameters as all matrix elements between orthonormal states are calculated exactly up to second order in the overlaps of the atomic orbitals involved. Our results reproduce the expected trends for the broadening and shift of the atomic level as the adatom approaches the surface, predicting a stable on-centre site adsorption with a binding energy of 4 eV.
