First-principles structures and stabilities of AlN+ (N = 46-62) clusters.

We present plausible candidates for the global minimum structures of Al(N)(+) (N = 46-62) cluster ions, determined by pseudopotential density functional theory static calculations under the spin-polarized generalized gradient approximation. Our calculations provide a first important step toward the rationalization of recent calorimetric experiments on the meltinglike transition of Al(N)(+). Most clusters with N > or = 48 clearly adopt fragments of the face-centered-cubic (fcc) crystalline lattice, although with significant distortions and a substantial proportion of defects in some cases. Another important driving force for stabilization comes from (111)-like surfaces, as the clusters often prefer to adopt less compact structures in order to keep the proportion of (100)-like surfaces at a minimum level. Al(46)(+) and Al(47)(+) adopt rather disordered structures instead. We find indications of enhanced stabilities for N = 51, 57, and 61 and of a substantial structural change between Al(55)(+) and Al(56)(+). These features correlate, albeit qualitatively, with the experimental observations.