<i>Ab Initio</i> Studies of Small Molecules Using 1<i>s</i> Gaussian Basis Functions. I. Exploratory Calculations

Abstract

Exploratory studies of the ground states of H2+, H2, He2+ +, and HeH+ using a basis of 1s Gaussian orbitals are presented. The emphasis is on the direct calculation of molecular wavefunctions with complete optimization of all parameters including the position and size of all orbitals. For the two-electron systems both self-consistent-field molecular-orbital and many-configuration studies are done. Results for total energies, MO orbital energies, and equilibrium bond lengths are satisfactory when compared to other variational studies of various degrees of accuracy, including some nearly exact studies. As expected, the larger nuclear charge in He2+ + and the lower symmetry of HeH+ make convergence slower than for H2+ and H2. Further examination of the H2 results is made by calculation of the averages of the nonenergy quantities x2, z2, and 1/r12.