Atom-bond pairwise additive representation for cation-benzene potential energy surfaces:: An ab initio validation study

The achievement of extensive and meaningful molecular dynamics simulations requires both the detailed knowledge of the basic features of the intermolecular interaction and the representation of the involved potential energy surface in a simple, natural and analytical form. This double request stimulated us to extend to ion-molecule systems a semi-empirical method previously introduced for the description of weakly interacting atom-molecule aggregates and formulated in terms of atomic species-molecular bond interaction additivity. The method is here applied to the investigation of the prototypical M+-C6H6 systems (M = Li, Na, K, Rb and Cs) and some of its predictions are tested against accurate ab initio calculations. Such calculations have been performed by employing the MP2 method and large basis sets, privileging the description of the metal atoms. The agreement between potential energy scans semiempirically obtained and ab initio results is good for all the investigated geometries, thus showing that the adopted representation is in general able to reproduce all the main features of the potential energy surface for these systems. The role of the various noncovalent interaction components, as a function of the geometry and of the intermolecular distance in the M+-C6H6 complexes, is also investigated for a more detailed assessment of the results of the semiempirical method.