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. @
