Energy and density analyses of the H2 molecule from the united atom to dissociation: The 1Σg+ states

The first 15 (1)Sigma(+)(g) states of the H-2 molecule are computed with full configuration interaction (CI) both from Hartree-Fock molecular orbitals and Heitler-London atomic orbitals; the computations are correlated with a comprehensive analysis. The basis sets utilized are extended and optimized Slater-type functions [Slater-type orbital (STO)] and spherical Gaussian functions [Gaussian-type orbital (GTO)]. The full CI computations cover the internuclear distances from 0.01 to 10 000 bohr. The available accurate data by Wolniewicz and co-workers for the first five excited states verify the quality of our computations. We focus on the characterization of the orbitals in the wave functions, on the electronic density evolution from the united atom to dissociation, on quantitative decomposition of the total energy into covalent and ionic components, and on detailed analyses of energy contributions to the total state energy from selected STO and GTO subsets. These analyses lead to study (with full CI) the H- negative ion with a proton and the H+H- ion pair systems. The ground and excited states for the He and H atoms and for the H- ion are computed to discuss the united atom and the dissociation products H(1s)+H(nl) of the n state manifolds. With the exception of n=1, each manifold has one state, specifically the EF, H, 7, and 11, whose second minimum has strong ionic character; state 11 dissociates as H+H-.