A detailed investigation on the global minimum structures of mixed rare-gas clusters: geometry, energetics, and site occupancy

Abstract

We performed a global minimum search of mixed rare-gas clusters by applying an evolutionary algorithm (EA), which was recently proposed for binary atomic systems (Marques and Pereira, Chem. Phys. Lett. 2010, 485, 211). Before being applied to the potentials used in this work, the EA was further tested against results previously reported for the Ar(N)Xe(38-N) clusters and several new putative global minima were discovered. We employed either simple Lennard-Jones (LJ) potentials or more realistic functions to describe pair interactions in Ar(N)Kr(38-N), Ar(N)Xe(38-N), and Kr(N)Xe(38-N) clusters. The long-range tail of the pair-potentials shows some influence on the energetic features and shape of the structure of clusters. In turn, core-shell type structures are mostly observed for global minima of the binary rare-gas clusters, for both accurate and LJ potentials. However, the long-range tail of the potential may have influence on the type of atoms that segregate on the surface or form the core of the cluster. While relevant differences for the preferential site occupancy occur between the two potentials for Ar(N)Kr(38-N) (for N > 21), the type of atoms that segregate on the surface for Ar(N)Xe(38-N) and Kr(N)Xe(38-N) clusters is unaffected by the accuracy of the long-range part of the interaction in almost all cases. Moreover, the global minimum search for model-potentials in binary systems reveals that the surface-site occupancy is mainly determined by the combination of two parameters: the size ratio of the two types of particles forming the cluster and the minimum-energy ratio corresponding to the pair-interactions between unlike atoms.