Energy and density analysis of the H2 molecule from the united atom to dissociation: The Σ3g+ and Σ3u+ states

The first 14 Σ3g+ and the first 15 Σ3u+ states of the H2 molecule are computed with full configuration interaction both from Hartree–Fock molecular orbitals and Heitler–London atomic orbitals within the Born–Oppenheimer approximation, following recent studies for the Σ1g+ and Σ1u+ manifolds [Corongiu and Clementi, J. Chem. Phys. 131, 034301 (2009) and J. Phys. Chem. (in press)]. The basis sets utilized are extended and optimized Slater-type functions and spherical Gaussian functions. The states considered correspond to the configurations (1s1nl1) with n from 1 to 5; the internuclear separations sample the distances from 0.01 to 10 000 bohrs. For the first three Σ3g+ and Σ3u+ states and for the fourth and fifth Σ3g+ states, our computed energies at the equilibrium internuclear separation, when compared to the accurate values by Staszewska and Wolniewicz and by Kolos and Rychlewski, show deviations of about 0.006 kcal/mol, a test on the quality of our computations. Motivation for this work comes not only fr...