Stabilities and structures of gas phase MgO clusters

Novel structures and energy spectra of hydroxylated (SiO2)8-based clusters: Searching for the magic (SiO2)8O2H3− cluster

The prominent (SiO(2))(8)O(2)H(3) (-) mass peak resulting from the laser ablation of hydroxylated silica, attributed to magic cluster formation, is investigated employing global optimization with a dedicated interatomic potential and density functional calculations. The low-energy spectra of cluster isomers are calculated for the closed shell clusters: (SiO(2))(8)OH(-) and (SiO(2))(8)O(2)H(3) (-) giving the likely global minima in each case. Based upon our calculated cluster structures and energetics, and further on the known experimental details, it is proposed that the abundant formation of (SiO(2))(8)O(2)H(3) (-) clusters is largely dependent on the high stability of the (SiO(2))(8)OH(-) ground state cluster. Both the (SiO(2))(8)O(2)H(3) (-) and (SiO(2))(8)OH(-) ground state clusters are found to exhibit cagelike structures with the latter containing a particularly unusual tetrahedrally four-coordinated oxygen center not observed before in either bulk silica or silica clusters. The bare ground state (SiO(2))(8)O(2-) cluster ion core is also found to have four tetrahedrally symmetric Si==O terminations making it a possible candidate, when combined with suitable cations, for extended cluster-based structures/materials.

Ab initio study on structural and electronic properties of BanOm clusters

Density-functional calculation within local density approximation, shows that the electronic property of a barium oxide cluster is strongly correlated with its equilibrium structure. The ground-state structures of BanOm (4 < or = n < or = 9,m < or = n) clusters can be classified into four categories: (a) compact, (b) dangling state, (c) F-center, and (d) stoichiometric. The compact cluster is metallic, almost no energy gap exists between the highest occupied and the lowest unoccupied molecular orbitals. The energy gap for the dangling state cluster is larger than that for the F-center cluster, while the stoichiometric cluster has the largest energy gap.

Impact-Induced Cleaving and Melting of Alkali-Halide Nanocrystals

Impact of nanocrystalline alkali-halide clusters against solid surfaces causes them to fission exclusively into low surface-energy fragments. In time-of-flight scattering experiments, this process appears at an impact energy so low that it must result from a single-step cleavage of the nanocrystal along low surface-energy cleavage planes. At higher energies (more than 1 electron volt per atom), a crossover occurs to an entirely different behavior-evaporative cascades that proceed irrespective of the structureenergetic properties of the fragments. These cascades, and the approximately linear scaling of the crossover energy with cluster size, are characteristic of impact-induced transformation of the cluster to a molten state. Collision with the high-rigidity surface of silicon gives a substantially greater cleavage probability than the soft basal-plane surface of graphite.