Extended pairwise additivity: interactions of degenerate atoms with rare-gas atoms

Abstract
The concept of pairwise additivity is extended to include one degenerate atom interacting with an arbitrary number of rare-gas atoms. The interaction is written as a matrix of dimensionality equal to the degeneracy. Adiabatic polyatomic energy surfaces are obtained by diagonalising the interaction matrix. The energy surfaces are compared to SCF calculations for the case of a lithium atom interacting with two helium atoms. Formulae are given for the addition of spin-orbit coupling.