AB-INITIO CALCULATIONS OF STRUCTURES AND STABILITIES OF (NAI)(N)NA+ AND (CSI)(N)CS+ CLUSTER IONS

Ab initio calculations using the perturbed ion model, with correlation contributions included, an presented for nonstoichiometric (NaI)(n)Na + and (CsI)(n)Cs+ (n less than or equal to 14) cluster ions. The groun d state and several low-lying isomers are identified and described. Ro cksalt ground states are common and appear at cluster sizes lower than in the corresponding neutral systems. The most salient features of th e 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 n=4, 6, 9, and 13. Finally, th e ionization energies and the orbital eigenvalue spectrum of two (NaI) (13)Na+ isomers are calculated and shown to be a fingerprint of the st ructure. [S0163-1829(98)03939-3].