Structural properties and quantum effects in protonated helium clusters. I. The ab initio interaction potential

Ab initio calculations are carried out, at various levels of treatment of c orrelation forces, for the orientation and distance dependence of the inter action between a helium atom and the structure of the ionic core found earl ier in protonated He cluster studies, i.e. the linear (HeHHe)(+) triatomic molecular ion. Several aspects of the potential energy surface are discusse d and specific details of the stable configuration analysed. The final ener gy surface is spline-fitted for further use in the stochastic calculations for the ground vibrational states of the small protonated clusters presente d in a following paper. (C) 2000 Elsevier Science B.V. All rights reserved.