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.