Rigorous theoretical investigation of the ground state of H2

A variety of results are reported for the ground state (X 1Σ+/sub g/) of the hydrogen molecule. They include improved Born-Oppenheimer calculations, a study of the convergence of energies with basis-set size, adiabatic calculations, and the first successful ab initio nonadiabatic calculation. The latter, which treats H2 as a four-body problem, leads us to predict that the dissociation energy of H2 is 36 117.92 cm-1. This value may be compared with 36 117.8 +- 0.4 cm-1 (the value derived from the experimental ionization potential), with 36 118.6 +- 0.5 cm-1 (the value derived from the experimental vibrational levels of the B 1Σ+/sub u/ state), or with 36 118.3 cm-1