Trends in Energies and Geometric Structures of Neutral and Charged Aluminum Clusters.

The minimum energy geometric structures of Aln, A[Formula: see text] , and A[Formula: see text] (4 ≤ n ≤ 15) are predicted from the results of "Tabu Search" (TS) global optimizations performed directly on the BPW91/LANL2DZ potential energy surface. In 24 of the 36 cases investigated, the TS delivered a lower energy structure than previously reported, in one case (A[Formula: see text] ) it failed to find the global minimum, and in the remaining 11 cases TS confirmed previous structures. All clusters (with 4 ≤ n ≤ 15) have the lowest spin state as their ground state except Al4 (triplet), A[Formula: see text] (quartet), A[Formula: see text] (triplet), and maybe A[Formula: see text] (singlet and triplet are degenerate). The 20-electron A[Formula: see text] and 40-electron A[Formula: see text] clusters are relatively stable compared to other clusters, on several criteria; to a lesser degree, Al7, Al12, and A[Formula: see text] are also stable.