Previous calculation of the ground-state energy of H2 has been extended to include large internuclear distances and accurate potential-energy curve for 0.4≤R≤10.0 a.u. is presented. For 0.4≤R≤4.0 a.u. expectation values of several operators have also been calculated. The calculation was made using a wavefunction in the form of an expansion in elliptic coordinates. The wavefunction depends on the interelectronic distance but, in contrast to the James—Coolidge expansion, is flexible enough to describe properly the dissociation of the molecule. Extensive calculations have also been made for the repulsive 3Σu+ state (1.0≤R≤10.0) and for the 1Πu state (1.0≤R≤10.0). In the former case a van der Waals minimum has been found at R=7.85 a.u. and 4.3 cm−1 below the dissociation limit. For the 1Πu state the computed binding energy De=20 490.0 cm−1 and the equilibrium internuclear distance Re=1.0330 Å are in a satisfactory agreement with the experimental values De=20 488.5 cm−1 and Re=1.0327 Å. In this case a van der Waals potential maximum has been found to occur at R=9.0 a.u. and 105.5 cm−1 above the dissociation limit. Preliminary results for the 1Σu+ state at R≈Re are also given.

Accurate ground-state energies of the hydrogen molecule have been computed using wavefunctions in the form of expansions in elliptic coordinates and including explicitly the interelectronic distance. The computations have been made with 54-term expansions (0.4≤R≤3.7) and with 80-term expansions (0.5≤R≤2.0). For the equilibrium internuclear distance, the best total energies obtained in the two cases are —1.1744701 a.u. and —1.1744746 a.u., respectively, the corresponding binding energies being 38 291.8 and 38 292.7 cm—1. Employing the 54-term wavefunctions, the relativistic corrections and the diagonal corrections for nuclear motion have been computed for several internuclear distances. For equilibrium their contributions to the binding energy have been found to be —0.526 and 4.947 cm—1, respectively. Thus the final theoretical binding energy for H2 amounts to 38 297.1 cm—1 and is a little larger than the experimental value 38 292.9±0.5 cm—1. The discrepancy may be due to the adiabatic approximation.

A variation perturbation method has been employed to calculate the static dipole polarizabilities of the hydrogen molecule. The wavefunction was represented by an expansion in elliptic coordinates including the interelectronic distance. A 54-term expansion was used for the zero-order wavefunction and 34 terms for the first-order corrections. The polarizabilities computed for several values of the internuclear distance (0.4≤R≤4.0) were averaged for various vibrational and rotational states of H2, HD, and D2. The results are in a satisfactory agreement with the experimental values.

The complete four-particle nonrelativistic Hamiltonian and 147-term wavefunctions have been used to compute the energies and the expectation values of several other operators for vibronic ground states and for the first vibrationally excited states of H2, D2, and T2. For H2 and D2 the computed dissociation energies, with relativistic corrections, are by 0.6 and 1.3 cm—1, respectively, larger than the experimental values.

The SCF analysis of few-body contributions to the energy of Be3, Be4, and Be5 clusters is presented. It is shown that nonadditive terms are decisive for the stability of such clusters. An explicit evaluation of the nonadditive five-body interaction is given.