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arXiv 1804.04030cond-mat.mtrl-sci
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用Wannier插值法从头计算位移光电流

Ab initio calculation of the shift photocurrent by Wannier interpolation

Julen Ibañez-Azpiroz, Stepan S. Tsirkin, Ivo Souza

摘要:

我们描述并实现了一个基于最大局域化Wannier函数的第一性原理算法,用于计算压电晶体在独立粒子近似下的位移电流响应。该算法提出了几个优点比现有的,包括全规范不变性,低计算成本,和正确的处理光学矩阵元与非局部赝势。带截断误差避免了仔细制定的$k\cdot p$扰动理论的子空间内的wannierized带。所需的成分是哈密顿量的矩阵元素和在Wannier基中的位置算子的矩阵元素,它们在Wannier化步骤结束时很容易获得。如果位置算子的非对角矩阵元素被丢弃,我们的表达式减少到最近紧束缚计算的移位电流中使用的那些。我们发现,这种“对角线”近似可以引入相当大的误差,突出的重要性,仔细嵌入紧束缚模型在真实空间中的电荷转移,引起的移位电流的准确描述。

英文摘要:

We describe and implement a first-principles algorithm based on maximally-localized Wannier functions for calculating the shift-current response of piezoelectric crystals in the independent-particle approximation. The proposed algorithm presents several advantages over existing ones, including full gauge invariance, low computational cost, and a correct treatment of the optical matrix elements with nonlocal pseudopotentials. Band-truncation errors are avoided by a careful formulation of $k\cdot p$ perturbation theory within the subspace of wannierized bands. The needed ingredients are the matrix elements of the Hamiltonian and of the position operator in the Wannier basis, which are readily available at the end of the wannierization step. If the off-diagonal matrix elements of the position operator are discarded, our expressions reduce to the ones that have been used in recent tight-binding calculations of the shift current. We find that this `diagonal' approximation can introduce sizeable errors, highlighting the importance of carefully embedding the tight-binding model in real space for an accurate description of the charge transfer that gives rise to the shift current.

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