Density Functional Theory Study Of B_n And B_nn Small Cluster Structure And Stability

During the past decade, the clusters of groupâ…¢-â…¤have been intensively studied, because the special electron configuration makes their properties rather unique. In this thesis, the structural and stable properties of boron and boron nitride small clusters were studied by density-functional theory (DFT).First of all, for the analysis of boron nitrogen bond characteristics, the potential energy curves for the ground state of BN molecules as well as their corresponding ions have been computed using DFT method with 6-311G* basis sets. The equilibrium geometries and disassociation energies also have been calculated. Its ground state is ³Î . Analytical potential energy functions of these states have been fitted using Murrell-Sorbie function. Second, Density Functional Theory (DFT) with B3LYP method at 6-31G* level was used to study the geometries and vibrational frequencies of B_n (n=2-8) clusters. Our results showed that most structures of B_n micro-clusters are planar forms. Planar configurations contain chain-like and ring-like forms. Thirdly, the geometric configurations, electronic structures, and vibrational frequencies of B_nN (n=1-8) clusters were studied at B3LYP/6-311G* level. Our calculations show that the ground states of B_nN clusters can be rapidly obtained by inserting nitrogen atom into two atoms at the peripheral sites in B_n clusters. The most stable optimized clusters hold planar configuration. Nitrogen atom prefers to bond with two atoms of boron atoms at the marginal positions. The dissociation energies and secondary energy differences of the ground states reveal that the B₂N and B₅N clusters are more stable than any others in this series.