Model-potential methods for the calculation of atom-rare-gas interaction: application to the H-He system

Abstract

The theory of model-potential methods is re-examined with particular reference to the calculation of the interaction of one-valence (or Rydberg) electron atoms with rare gases. It is shown that the use of a purely local potential to represent the rare-gas core may lead to spurious curve crossings in the molecular calculation. Such difficulties can be avoided by the introduction of a non-local term which simulates the Pauli principle, a procedure equivalent to constraining the model-potential wavefunction to be orthogonal to the one-electron orbitals of the inner shells. The theory is applied to obtain a model potential for He, optimised to the best available electron scattering data. This model potential is subsequently used to calculate the long and intermediate range interaction of the x 2 Sigma ground state of H-He. The potential well depth (0.39 meV) at 7 a 0 is in excellent agreement with the best experimental and theoretical determinations.