Ab Initio SCF–MO–CI Calculations for H−, H2, and H3+ Using Gaussian Basis Sets

Fixed-center Gaussian-type functions (GTF) have been used as basis sets in an extensive SCF–MO–CI study on H−, H2, and H3+. An accurate description requires 4 or 5 s-GTF on each center, plus at least one set of p-GTF, which are essential for the reproduction of reliable potential curves; d-GTF are, however, of minor importance. A constant p exponent may be used successfully in a wide variety of nuclear configurations. Variational energies of − 1.3397 and − 1.2765 hartree were calculated for the most stable equilateral and collinear geometries of H3+. A potential-energy surface has been computed for the reaction H+ + H2, to an accuracy of about 2 kcal mole−1 over its important regions. In the computation of the proton affinites of H− and H2, little accuracy was lost when a limited basis set was used in SCF calculations.