Global Optimization Of Cluster Structures Based On Genetic Algorithm

Clusters are the intersection of physics, chemistry and materials. It's a hot region in recent years. The basis of studying clusters is to know their structures, but it is a complex problem and is the most difficult point now in cluster studying. It is complicated to determine their structures and it is the electronic structures, which are mainly studied by theoretical calculations. In this work, genetic algorithm combined density functional theory is uesd to study Ga, NaSi and WO3clusters systematically. We gave their ground state structures and the grow pattern. Then we studied their electronic properties.The melting point of Ga cluster is higher than Ga bulk. This abnormal phenomenon attracts many researchers. In chapter three, using genetic algorithm incorporated with density functional theory, we have explored the size evolution of structural and electronic properties of neutral Ga clusters of20-40atoms with their electronic properties. In the size range studied, the Gan clusters exhibit several grow patterns, and the core-shell structures become dominant from Ga31. With high point group symmetries, Ga23and Ga36show particularly high stability and Ga36owns a large HOMO-LUMO gap.Si is the most important semiconductor. Na atoms adsorb on Si surface gained people's attention. There are many theoretical and experimental works on NaSi clusters. In chapter four, the ground state structures of neutral and anionic clusters of NanSim (1≤n≤3,1≤m≤11) have been determined using genetic algorithm incorporated in a first principles total energy code. The size dependence of the structural and electronic properties is discussed in detail. It is found that the lowest-energy structures of NanSim clusters resemble those of the pure Si clusters. Interestingly, Na atoms in neutral NanSim clusters are usually well separated by the Sim skeleton, whereas Na atoms can form Na-Na bonds in some anionic clusters. The ionization potentials, adiabatic electron affinities, and photoelectron spectra are also calculated and the results compare well with the experimental data.WO3is an important material for photocatalysis. The previous study of (WO3)n clusters are limited to n<6. We performed a global search for the most stable structures of (WO3)n clusters for n=2-12. Small (WO3)n clusters with n=3or4adopt ring-like configurations with W-O alternating arrangement, which are indeed the building units of bulk WO3solids. Starting from (WO3)8, the tungsten oxide clusters transform to symmetric spherical-like cages, in which each W atom coordinates with five O atoms and O atom either serve as bridge between two W sites or form a terminal W-O bond pointing outward the spherical surface. The size dependence of relative stability, HOMO-LUMO gap, electronic states of these (WO3)n clusters were discussed. Analysis of wavefunctions of frontier orbitals and electron density of states shows that the valence bands are dominated by the2p electrons from oxygen and the conduction bands are mainly contributed by the5d states from tungsten. We also construct WO3nanotubes based on the structure pattern of WO3clusters.The present work are important for deep understanding the base structure of different bond type clusters, exploring the grow pattern of clusters and related nano structures and explaining the experiment data.