A SIMPLE METHOD TO CALCULATE POTENTIAL CURVES OF 2-ELECTRON MOLECULESAT INTERMEDIATE NUCLEAR DISTANCES

A simple configuration interaction method to calculate accurate electr onic energies. of two-electron molecules at intermediate internuclear distances is presented. The correlated basis functions are constructed from H-2(+) molecular orbitals (exact solution of the two-centre Coul ombic problem), and include an explicit dependence on the interelectro nic distance in order to describe the major part of the electronic cor relation. The first Green transformation is used to give an important simplification of the expression for the matrix elements of the Hamilt onian. The method is shown to give accurate energies for the H-2 molec ule in the ground (1) Sigma(g) State at intermediate distances, and is applied to determine new potential curves of highly excited states. T he simplicity of the wavefunction will allow it to be used relatively easily in subsequent calculations of dynamical properties.