Density-functional global optimization of (La2O3)n clusters.

Structures of stoichiometric (La(2)O(3))(n) (n = 1-6) clusters have been systematically studied by theoretical calculations. Global minimum structures for these clusters are determined by genetic algorithm based global optimizations at density functional level. The ground state structure for La(6)O(9) was found to be highly symmetric with point group O(h) and the centered oxygen atom has the coordination number as large as six, which is the same as the highest coordination number of oxygen atoms in bulk La(2)O(3). Analysis of the binding energies shows that La(6)O(9) has a high stability among the studied clusters. The energies of the highest occupied∕lowest unoccupied molecular orbitals, vertical ionization energy, and vertical electron affinity of each cluster are provided. Electronic structure of La(6)O(9) is discussed by analysis of the frontier molecular orbitals and unpaired spin density distributions of charged clusters.