Ab initio calculations of structures and stabilities of (NaI) nNa1 and ( CsI) nCs1 cluster ions

Abstract

Ab initio calculations using the perturbed ion model, with correlation contributions included, are presented for nonstoichiometric (NaI)nNa1 and (CsI)nCs1 (n<14) cluster ions. The ground state and several low-lying isomers are identified and described. Rocksalt ground states are common and appear at cluster sizes lower than in the corresponding neutral systems. The most salient features of the measured mobilities seem to be explained by arguments related to the changes of the compactness of the clusters as a function of size. The stability of the cluster ions against evaporation of a single alkali halide molecule shows variations that explain the enhanced stabilities found experimentally for cluster sizes n54, 6, 9, and 13. Finally, the ionization energies and the orbital eigenvalue spectrum of two (NaI)13Na1 isomers are calculated and shown to be a fingerprint of the structure. @