A systematic theoretical study of stoichiometric clusters (NaI)(n) up
to n = 15 is performed using the ab initio perturbed-ion (PI) model. T
he structures obtained are compared to previous pair potential results
, and observed differences between (NaI)(n) clusters and previous ab i
nitio results for other alkali halide clusters are discussed. (NaI)(n)
clusters with n up to 15 do not yet show a marked preference for geom
etries which are fragments of the bulk lattice. Instead, stacks of hex
agonal rings or more open structures are obtained as ground structures
in clusters with n = 3, 6, 7, 9, 10, 12, 13, and 15, indicating that
convergence to bulk structure is not achieved yet at this size range.
Low-lying isomers, which are fragments of the crystal lattice, exist,
nevertheless, for those cases. The binding energies show that clusters
with n = 4, 6, 9, and 12 molecules are specially stable. The binding
energy has been decomposed in contributions which allow for an intuiti
ve interpretation. Some electronic properties like ionization potentia
ls and electronic energy levels are also studied.