Many-orbital cluster expansion for the exchange-repulsion nonadditivity in the interaction of rare gas atoms. The neon trimer

Nonadditivity of the exchange repulsion for three neon atoms in the equilateral triangle configuration has been calculated in the first-order of the symmetry adapted perturbation theory. The relative nonadditive contribution to the first-order interaction energy has been found to be about twice as small as in the helium trimer. The many-orbital cluster partition of the exchange nonadditivity has been derived. It has been found that in the region of the van der Waals minimum about 95% of the exchange nonadditivity originates from the interaction of the L-shell electrons only. The five-orbital terms as well as terms of an order-higher than S³ have been found to be negligible. Approximate formulae for evaluation of the exchange repulsion nonadditivity has been proposed and discussed.This work was partly supported by the Polish Academy of Sciences within the project MR.I.9.