纤锌矿结构AlN、GaN及ZnO自发极化的第一性原理研究

摘要

根据现代极化理论,分别利用Berry phase方法和最大局域化Wannier函数方法系统计算了纤锌矿结构AlN、GaN及ZnO中的自发极化,并从电子项和离子项引起的极化变化具体分析了自发极化的起源.研究表明AlN自发极化中电子项的贡献占据主导地位,而GaN及ZnO自发极化中以离子项的贡献为主.研究发现其他文献计算自发极化时,由于计算模型和参考模型使用相同的体积,导致计算结果偏小.利用Wannier中心,从结构中最小重复单元的电偶极矩出发对原有计算公式进行了修正,使得自发极化的计算结果更趋合理.研究发现在特定建模条件下,可以不用计算参照模型中的极化,利用Wannier中心确定纤锌矿结构中正负电荷的重心,通过经典的静电学理论直接计算出自发极化,直观解释了自发极化的形成.%By using Berry phase and maximally localized Wannier functions methods based on the modern polarization theory,the spontaneous polarization of w urtzite AlN,GaN and ZnO are calculated respectively.T he origin of spontaneous polarization is studied from the polari-zation variation of ionic and electronic part.It is found that the spontaneous polarization of AlN is primarily from the electronic part,w hile the spontaneous polarization of GaN and ZnO is mainly from the ionic part.Since the computational model and reference model have a same volume in the literature,it is found that the result is reduced compared with our result.On the basis of the discussion of local dipole,a correction formula is given to make the calcula-tion more reasonable.Using the charge depth of the formula unit,we also proposed a new method to directly calculate the spontaneous polarization of wurtzite structure without the computation of reference structure.The production of the spontaneous polarization can be in-tuitively explanation in terms of this method.