Ann-valued representation of He+npotentials

Abstract
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 He2, He+ 2, He3 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 structure and classical dynamics to be studied.