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 x2 Sigma ground state of H-He. The potential well depth (0.39 meV) at 7 a0 is in excellent agreement with the best experimental and theoretical determinations.

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