P轨道占位库仑排斥对Mg<sub>2</sub>Sn电学性质的影响

Abstract

利用基于密度泛函理论的广义梯度近似方法计算了Mg2Sn的能带结构、能态密度、差分电荷密度和介电函数。为了考虑Sn中5p轨道的强电子关联效应，我们采用GGA + U的方法计算Mg2Sn的电学性质。当有效U值为0 eV时，Mg2Sn带隙为负，与实验值相差较大。当有效U值为1.88eV时，间接带隙为0.30 eV，与实验值吻合较好。差分电荷密度的计算表明Mg2Sn中Sn-Sn键相对于Sn-Mg键有着较强的共价性，符合实际情况，介电函数的计算结果也与实验结果基本一致。这些证实p轨道占位库仑排斥对Mg2Sn的电学性质有着较大的影响。The band structure, density of states, electron density difference and dielectric function of Mg2Sn are investigated systematically by using the generalized gradient approximation based on density functional theory. To describe the strong electron correlation in the Sn 5p states, the GGA plus on-site repulsion method (GGA+U) is used in the electrical properties calculation of Mg2Sn. It is found that the band gap is negative with the effective U value of 0 eV, which is quite different from the experimental result. As the effective U value of 1.88 eV is considered, the compound is a semi-conductor with an indirect band gap of 0.30 eV, which agrees with the previous experimental ob-servation satisfactorily. The calculations of electron density difference show that the covalent bond between Sn-Sn is stronger than the covalent bond between Sn-Mg, which is accordant with the practical situation. The calculation of dielectric function agrees well with the experimental result, too. The important influence of the p-orbital on-site Coulumb repulsion for the electronic properties of Mg2Sn is confirmed.