Theoretical Study On The Stability And Electronic Structure Of Li-coated B₁₆N₁₆ Clusters

The nanostructure materials have been widely applied in various fields in recent years, especially that synthesized by the lighter elements B and N. They have become a hot spot in the relative research for the high chemical stability, the advantages of larger specific surface area and unique electronic structure. Lots of physical and chemical properties of clusters varies with the clusters size, so the key to study the clusters is to find clusters that have more stable geometrical structure and analyze its electronic structure.Based on the method of density functional theory B3 LYP/6-31?d, p?, this paper has firstly studied the geometry of Li coated B₁₆N₁₆ clusters' stability, considering the inequivalence of B and N atoms, B-N bridge and vacancy on the link as the initial position of Li atomic in the B₁₆N₁₆ structure. Then optimize all of the B₁₆N₁₆Li_n?n=12,3,4,6,12? structures and get the most stable structure in the system.The results show that the best binding of all Li atoms on the surface of clusters B₁₆N₁₆ is B-N key between adjacent hexagon ring and yuan ring, namely R46 and R66 bridge site. And the system will be the most stable when two Li atoms in the same B atoms connected B-N key. The average binding energy of single Li atoms is between 0.92 and 1.12eV, and the binding energy of each Li atom in Li₂, Li₃, Li₄ is 0.44eV,0.46eV, and 0.61eV based on the same calculation method. Obviously, the interaction between Li atoms and B₁₆N₁₆ clusters is stronger than that among Li atoms.So Li atoms in clusters B₁₆N₁₆ surface will be independent distribution, and will not gather together as transition metal atoms in the body surface.By analyzing the charge of NBO?natural bonding orbital? in Li atom, it is found that when carried two, four, six and twelve Li atoms, the Li atom in the most stable structure take charge of 0.72e, 0.70e, 0.59e and 0.50e, respectively.When carried three Li atoms, the charge reduce to about 0.45e as a result of Li atoms close to each other.This result shows that when combining to B₁₆N₁₆ clusters, Li atom will transfer electrons to the clusters, increasing repulsion between the electrons in the Band N atoms. Ccompared with the undecorated B₁₆N₁₆ cage, all the B-N bond length increase from 1.46 A to 1.63 A. Finally, by analizing the total states density and Listate density of B₁₆N₁₆Li_n?n = 1,2,3,4,6,12? system, it is shown that it can occupy the orbital which has three energy bands, two low energy bands are as same as the pure B₁₆N₁₆, mainly from 2s of N, 2s2p of B and 2p of N. The highest energy band is occupied by 2s of Li. With the increase of Li atoms, the number of electrons transfer from Li atom to clusters reduce, the HOMO energy levels formed by 2s of Li rise, and the band gap value gradually reduce.