Theory of ionization potentials of nonmetallic solids
Theory of ionization potentials of nonmetallic solids
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非金属固体电离势理论
DOI：
10.1103/physrevb.95.125309
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发表时间：
2017
影响因子：
3.7
通讯作者：
and F. Oba
中科院分区：
文献类型：
--
作者：
Y. Kumagai;K. T. Butler;A. Walsh;and F. Oba
由于电离势是固体中的基本量之一，决定着固体的物理化学性质和电子器件的性能，近年来，许多研究人员利用平板模型的第一性原理计算来量化电离势。然而，大量和表面贡献的细分仍然是一个有争议的问题。在这项研究中，我们讨论了如何利用宏观平均技术将IP分解为体贡献和表面贡献。虽然这一过程量化了定义明确的宏观偶极子，并与连续模型进行了验证，但与物理直觉并不一致。这是因为固体内部强烈的电荷涨落对宏观偶极势有很大的贡献。我们还讨论了另一种与物理直觉一致的分裂过程的可能性，并得出结论：只有当体电荷密度和表面电荷密度都很好地分解为球形电荷的叠加时，这才是可能的。在后半部分中，我们使用原子电荷近似和分子电荷近似，将固体的电荷密度分别描述为组成原子和分子的电荷密度的叠加，从而评估了典型的半导体和绝缘体，如硅、金刚石、砷化镓、氮化镓、氧化锌和氧化镁的IPs。我们发现，原子-电荷近似，也称为模型-固体理论，可以成功地再现共价材料的激发态，但对离子材料效果不佳。另一方面，分子电荷近似部分考虑了从阳离子到阴离子的电荷转移，总体上表现出更好的预测性能。
Since the ionization potential (IP) is one of the fundamental quantities in a solid, ruling the physical and chemical properties and electronic device performances, many researchers have quantified the IPs using first-principles calculations of slab models recently. However, the breakdown into bulk and surface contributions has remained a contentious issue. In this study, we discuss how to decompose the IP into the bulk and surface contributions by using the macroscopic average technique. Although this procedure quantifies well-defined macroscopic dipoles and corroborates with the continuous model, it is not consistent with the physical intuition. This is because the strong charge fluctuation inside solids significantly contributes to the macroscopic dipole potential. We also discuss the possibility of an alternative splitting procedure that can be consistent with the physical intuition, and conclude that it is possible only when both bulk and surface charge density is well decomposed into a superposition of spherical charges. In the latter part, we evaluate the IPs of typical semiconductors and insulators such as Si, diamond, GaAs, GaN, ZnO, and MgO, using atomic-charge and molecular-charge approximations, in which the charge density of a solid is described as a superposition of charge density of the constituent atoms and molecules, respectively. We find that the atomic-charge approximation also known as the model-solid theory can successfully reproduce the IPs of covalent materials, but works poorly for ionic materials. On the other hand, the molecular-charge approximation, which partly takes into account the charge transfer from cations to anions, shows better predictive performance overall.