NbB_2(0001)表面性质的第一性原理研究

First-principles Study on Characteristics of NbB_2(0001) Surface

应用密度泛函理论的第一性原理的方法分析了两种不同终端的NbB2(0001)表面的几何结构和电子结构。结果表明:两种不同终端的(0001)表面结构弛豫主要发生在前三层,并且硼终端的表面弛豫程度小于铌终端表面的弛豫。表面能分析结果表明,终止于硼终端的(0001)表面结构在更宽的范围内具有较低的表面能,即硼终端的(0001)表面比铌终端的表面更稳定。进一步分析NbB2(0001)两种终端表面的电子结构表明:在金属铌和硼之间发生了电子转移,加强了化学键的相互作用,导致第一间层向内弛豫。对于铌终端的表面第一层铌转移到第二层的电子数比硼终端表面第二层铌转移到第一层的电子数多,这是导致铌终端表面弛豫程度大于硼终端表面的主要原因。

The geometry and electronic structure of two different terminations on NbB2（0001） surfaces were calculated by the first principles based on density functional theory.The results indicated that there were obvious relaxations at the top three layers for both termination surfaces,and the outermost interlayer relaxations for B-terminated surfaces are much smaller than those for Nb-terminated surfaces.The surface energy results showed that the surface energy of B-terminated was lower than Nb-terminated surface in most of the range of μslabB.Therefore B-terminated surface was more favorable than Nb-terminated surface.To further analyze electronic structures of NbB2（0001） surfaces,chemical bonding was strengthened due to electrons＇ transfer between Niobium and boron atoms.As a result the first layer was contracted and electrons transfer in Nb-terminated surface was gtreater than B-terminated surface,which is the main reason that relaxation of Nb-terminated surface was larger than B-terminated surface.