An evolutionary algorithm was used to search for the low-energy structures of Li + Ar n and Li + Kr n (n = 1 − 14). Two functions were used to describe the interaction potential at the CCSD(T)/augcc-pVQZ level of theory: one is based on a sum of all pair potentials, whereas the other includes three-body interactions. In general, the global minimum structures are similar for both Li + Ar n and Li + Kr n . Modifications in the octahedral structure of the first solvation shell lead to a high-energy penalty. Conversely, the second solvation shell shows a panoply of minima with similar energies that are likely to be interconverted. Post-optimization at the MP2 level confirmed that, for n = 2 and 3, one has to include three-body terms in the potential to reproduce the low-energy structures. Additionally, MP2 calculations indicate that energy reorder of the global minimum structure observed for Li + Kr 8 is related to the Kr 3 Axilrod-Teller-Muto term included in the potential.ab initio calculations, clusters, evolutionary algorithm, geometry optimization, microsolvation
| INTRODUCTIONSolvation is a complex phenomenon with great relevance for the broad area of chemical physics. It is intimately related with the interactions that can be established among solute and solvent molecules, although the contribution from entropic effects can only be correctly described when incorporating all degrees of freedom of the system. Two main theoretical approaches are followed in the study of solvation: (1) continuum solvation models that do not treat solvent molecules as individual entities; and (2) explicit microsolvation methodology, where the solvent molecules are successively added to the system. Although the continuum models are able to incorporate the polarization of the solvent, they cannot explicitly describe interactions with a strong directional character and, in this way, environments comprising several solvents, ionic solutes, and biological systems are difficult to be accounted for. To somehow reduce these drawbacks, continuum-solvent methods [1] have been improved to approximately incorporate the structure of the solvent, [2] as well as the formation of the cavity for solute and the dispersion interaction by Abbreviations: ATM, Axilrod-Teller-Muto; aug-cc-pVQZ, augmented correlation consistent with polarized-valence quadruple-zeta basis set.; BSSE, basis set superposition error; cc-pVQZ, correlation consistent with polarized-valence quadruple-zeta basis set; CCSD(T), couple cluster with singles and doubles and perturbated triples excitations; EA, evolutionary algorithm; MP2, second-order Moller-Plesset.