A Study Of Ti_n(n=2-25) Clusters By CALYPSO Method

Cluster is relatively stable microscopic or sub-microscopic condensed matterslinked by different physical or chemical interactions, which consist of less thanseveral or more than thousands of atoms, molecules or ions. It is widely distributed innature and practice of human activity that involves many processes and phenomena,such as catalytic combustion, crystal growth, nucleation, coagulation, criticalphenomena and phase transitions. As a new level of physical structure, cluster has aseries of special physical or chemical properties which are different from theindividual atoms or molecules and macroscopic solids and vary with the number ofatoms contained in clusters. Research on the formation mechanism of clusters, clusterstructure and nature can not only promote the development of physics, chemistry andmaterials science, but also open up new avenues for the synthesis and development ofnew materials with special functions. As we all know, the special physical andchemical properties of cluster is closely linked with its microstructure. Therefore, it’salways the hot topic research in the field to determine the structure of clusters and tostudy the structure of atoms with the variation of the clusters. Currently, there are stillmany difficulties and challenges in experiments only with measurement to determinethe geometry structures of clusters. In this case, it is necessary to determine or predictthe structure of clusters by simulation. Theoretical structure prediction can not onlyassist experimental measurements to determine the cluster structure, but also canpredict new clusters with exotic physical and chemical properties prior to experimentwhich can serve as the useful guidance for experimental synthesis.As a relatively lighter transition metal element, titanium with good chemicalstability and resistance to high or low temperature, anti-acid, anti-alkali, as well asthe characteristics of high strength and low density, is hailed as a "space metal "which has the important industrial applications. Titanium clusters no only havecatalytic properties, but also present magnetic properties which do not appear in bulkmaterials, thus they have many potential applications. Determining the structure of titanium clusters and exploring the relation between structure evolution and thephysical and chemical properties can not only provide important knowledge base forthe comprehensive understanding of the transition metal clusters, but also have muchsignificance for its practical applicationUtilizing our group self-developed calypso (Crystal structure AnaLYsis by ParticleSwarm Optimization) algorithm in conjunction with density-functional theory, wehave performed extensive structure and properties research on Tin(n=2-25) clustersand proposed the ground state structures for Tin(n<=25) cluster. The results show thatthe clusters after Ti16gradually formed a core-shell structure whose surface arecovered by a pentagonal or hexagonal pyramid and the icosahedral structure can notbe stable. The binding energy calculations indicate that the Ti7, Ti13, Ti15structures aremore stable than their neighboring structures which shows that they are probablymagic number structures. These results are in excellent agreement with the previousexperimental mass resolved intensity spectrometry. We also propose that Ti9, Ti17andTi20structure may also be magic number structures. By calculating the electronicproperties, we found that magnetism will reduce gradually with the increasing numberof titanium cluster, and disappear entirely after Ti18.