First Principles Study Of Structures And Stabilities Of Boron Carbide Clusters

As excellent physical properties of boron-doped graphene are discovered, the research of boron carbide clusters is becoming more and more important. In this thesis, the lower-energy structures and relative stabilities of BnCm(n+m=2-10) and (BC)n(n=1-13) have been systematically explored using first principles calculations based on density functional theory. Our research shows:(1) the lowest-energy geometries of BnCm(n+m=2-10) clusters tend to form planar structures(wheel-type and cyclic structures), and only few forms quasi-planar and linear structures. As for BHCm(n+m<7) clusters, the lowest-energy geometries are all planar cyclic structures and their geometries are similar. As for BnCm (n+m>7) clusters containing the same atomic number, the lowest-energy geometries undergo wheel-type to cyclic structure transition as the number of carbon atoms increases and boron atoms decreases. When clusters contain few carbon atoms and remaining carbon atomic number unchanged, the lowest-energy geometries of clusters turn planar cyclic into wheel-type structures with the increase of boron atomic number. When clusters contain few boron atoms and remaining boron atomic number unchanged, the lowest-energy geometries of clusters are planar cyclic structures with the increase of carbon atomic number. The second lower-energy geometries are linear geometries with boron atoms at the terminal of the chain.(2) The stabilities of (BC)m(n=1-13) clusters have been discussed by calculating the binding energy per atom and second order energy differences as well as HOMO-LUMO gap. The results show that the average binding energy increases as the value of n increases. The second order energy differences and HOMO-LUMO gap suggest that (BC)n (n=1-13) with even n have relatively higher stability.