Density Functional Theory Studies On The Structures And Electronic Properties Of Mo And Mo₂N Clusters

Clusters are the agglomerates of a few to a few thousand atoms with relative stability. Clusters are the borderland between the microscopic single atom and the macroscopic solid state, exhibiting extraordinary size-dependent physical and chemical properties. One can design new materials using clusters as the building blocks. A number of intense studies have been performed on molybdenum clusters in recent years. Clusters have potential application as building blocks for functional nanostructure materials, electronic devices, and nanocatalysts, and they can serve as a model for systematic understanding of structure/property evolution.Structural evolution and electronic properties of Mo_n(n=2-10) clusters and Mo_2nN_n(n=1-5) clusters have been explored using density functional theory(DFT) methods. In the DFT calculations, exchange-correlation interactions were approximated by the generalized gradient approximation (GGA) with PW91 parameterization. A DFT semi-core pseudopotential (DSPP), and a double numerical basis set plus d-polarization functions (DND), as implemented in the DMol³ package were employed. We denoted this scheme as PW91/DSPP/DND.For Mo_n(n=2-10) clusters, the results showed that the linear structures have a strong tendency to form dimmers and the even number clusters were more stable than their neighboring odd number clusters; in the planar structures, the odd number clusters were stable in zigzags and the even number clusters; in the planar structures, the odd number clusters were stable in zigazags and the even number clusters were stable in polygons; 3D structures were the most stable among all dimensions. Only Mo3 and Mo8 had 2μB magnetic moments in the ground state structures. According to the results of the second order deference of total energies, vertical ionization potential and energy gaps, the magic number of the Mo_n(n=2-10) clusters was 5. Analyzed the thermodynamic properties of magic number cluster Mo5 showed that the standard thermodynamic functions in creased with the temperatures increasing. As far as Mo_2nN_n(n=1-5), The resulting equilibrium geometries show that the lowest-energy structures are dominated by a central core which corresponds to the ground state of Mo_n(n=2, 4, 6, 8, 10) clusters and nitrogen atoms which surround this core. The average binding energy, adiabatic electron affinity (AEA), vertical electron affinity (VEA), adiabatic ionization potential (AIP) and vertical ionization potential (VIP) of Mo_2nN_n(n=1-5) clusters have been estimated. The HOMO-LUMO gaps reveal the clusters have strong chemical activity. An analysis of Mulliken charge distribution shows that charge-transfer moves from Mo atoms to N atoms and increases with the cluster size.The present results provide useful insight into understanding the structural evolution and electronic properties of molybdenum clusters and molybdenum nitride clusters. They can give some useful information for the experimental studies.