Perturbation Treatment of the Ground State of the Hydrogen Molecule

Perturbation theory is used to obtain approximate energies and wavefunctions for the hydrogen molecule ground state. A function of simple form is chosen as zero-order function, the zero-order Hamiltonian is constructed, and the variational equation for the first-order wavefunction is solved approximately by expansion in James—Coolidge basis functions, yielding the second- and third-order energies. All integrals are calculated numerically. The binding energy and equilibrium internuclear distance are fair, but not as good as what one obtains from a comparable variational calculation.