Induction effects in metal cation-benzene complexes.

The role of polarization in the stabilization of a series of biologically relevant alkali and alkaline-earth metal cations (Li(+), Na(+), K(+), Mg(2+) and Ca(2+)) with the pi-electron distribution of benzene is examined by means of MP2 computations using Sadlej's basis set. In all cases a full description of the energy profile for the approach of the metal cation along the axis normal to the molecular plane of benzene has been performed. Analysis of the different contributions to the interaction energy, performed within the framework of the symmetry-adapted perturbation theory (SAPT), illustrates the important role of the induction component in the definition of the geometrical and energetic properties of the pathway leading to the formation of cation-pi complex. Finally, the ability of classical polarization models based on models of implicitly and explicitly interacting distributed isotropic polarizabilities to describe the induction term has been examined and discussed in the context of the generation of new polarizable force fields.