α-Al_2O_3(0001)表面弛豫及其对表面电子态的影响

The Relaxation of α-Al_2O_3(0001) Surface Impacts on Its Electronic States

在周期边界条件下的κ空间中 ,采用基于密度泛函理论的局域密度近似平面波超软赝势法 ,对最外表面终止层为单层Al的α Al2 O3 超晶胞 (2× 2 ) (0 0 0 1)表面结构进行了弛豫与电子结构计算研究 .结果表明 ,最外表面Al-O层有较大的弛豫 ,明显地影响了表面原子与电子结构 ,布居分析表明表面电子有更大的几率被定域在O原子的周围 ,表现出O的表面态 .进一步分析了表面弛豫前后表面电子密度、态密度变化 ,表面能级分裂主要来自于O的 2 p轨道电子态变化 .通过对比弛豫前后的表面电子局域函数 (ELF)图 ,分析了表面成键特性 .

The relaxation and electronic structure of the α-Al 2O 3(0001) super-cell (2×2) surface with single Al atoms layer-terminated are studied using ab initio quantum-mechanical calculations based on the density-functional theory and pseudopotential method. The calculations employ slab geometry and periodic boundary conditions, with the occupied orbitals expanded in plane waves. It′s found that the surface relaxation results in the change of surface electronic states by investigating the relaxation and the population of the Al-O atoms of the surface. By analyzing the difference of the density of state and electron charge density between the unrelaxed and relaxed surface, it is obvious that the α-Al 2O 3(0001) crystal surface appears on the O-surface state from which is most contribution to the O 2p states, and the surface electronic density plotted by electron localization function(ELF) shows the characteristics of surface bonding atoms. The ELF indicates the outmost Al-O ionic bonds of the relaxed surface are much stronger than that of the unrelaxed surface.