Fukushima T, Katayama-Yoshida H, Sato K, Bihlmayer G, Mavropoulos P, Bauer D S G, Zeller R, Dederichs P H
Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
J Phys Condens Matter. 2014 Jul 9;26(27):274202. doi: 10.1088/0953-8984/26/27/274202. Epub 2014 Jun 17.
On the basis of constrained density functional theory, we present ab initio calculations for the Hubbard U parameter of transition metal impurities in dilute magnetic semiconductors, choosing Mn in GaN as an example. The calculations are performed by two methods: (i) the Korringa-Kohn-Rostoker (KKR) Green function method for a single Mn impurity in GaN and (ii) the full-potential linearized augmented plane-wave (FLAPW) method for a large supercell of GaN with a single Mn impurity in each cell. By changing the occupancy of the majority t2 gap state of Mn, we determine the U parameter either from the total energy differences E(N + 1) and E(N - 1) of the (N ± 1)-electron excited states with respect to the ground state energy E(N), or by using the single-particle energies for n(0) ± 1/2 occupancies around the charge-neutral occupancy n0 (Janak's transition state model). The two methods give nearly identical results. Moreover the values calculated by the supercell method agree quite well with the Green function values. We point out an important difference between the 'global' U parameter calculated using Janak's theorem and the 'local' U of the Hubbard model.
基于约束密度泛函理论，我们对稀磁半导体中过渡金属杂质的哈伯德U参数进行了从头算，以GaN中的Mn为例。计算通过两种方法进行：（i）针对GaN中单个Mn杂质的科林加 - 科恩 - 罗斯托克尔（KKR）格林函数方法，以及（ii）针对每个晶胞中含有单个Mn杂质的GaN大超胞的全势线性缀加平面波（FLAPW）方法。通过改变Mn的多数t2能隙态的占据情况，我们从相对于基态能量E(N)的(N ± 1)电子激发态的总能量差E(N + 1)和E(N - 1)来确定U参数，或者通过使用电荷中性占据n0周围n(0) ± 1/2占据的单粒子能量（贾纳克过渡态模型）来确定。这两种方法给出了几乎相同的结果。此外，通过超胞方法计算的值与格林函数值相当吻合。我们指出了使用贾纳克定理计算的“全局”U参数与哈伯德模型的“局部”U之间的一个重要区别。
