AN N-VALUED REPRESENTATION OF HE-N(+) POTENTIALS

A formalism is proposed for the potential energy functions of rare gas cluster ions which is a modification of the DIM approach by explicit inclusion of 3-body terms. Functional forms have been derived for the 2-body and 3-body matrix elements of He-n(+) by fitting to accurate ab initio data on He-2, He-2(+), He-3 and He-3(+). Calculations on He-4( +) suggest that 4-body terms are unimportant for low energy regions of the potential energy surface. The model provides a route to the rapid evaluation of potentials for large He-n(+) clusters, allowing their s tructure and classical dynamics to be studied.