Department of Physics and I3N, University of Aveiro, Campus Santiago, 3810-193 Aveiro, Portugal.
Institute of Mathematical Problems of Biology, Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, Vitkevicha Street 1, Pushchino, 142290 Moscow Region, Russian Federation.
J Chem Phys. 2018 Apr 21;148(15):154706. doi: 10.1063/1.5025329.
Hydroxyapatite (HAp) is an important component of mammal bones and teeth, being widely used in prosthetic implants. Despite the importance of HAp in medicine, several promising applications involving this material (e.g., in photo-catalysis) depend on how well we understand its fundamental properties. Among the ones that are either unknown or not known accurately, we have the electronic band structure and all that relates to it, including the bandgap width. We employ state-of-the-art methodologies, including density hybrid-functional theory and many-body perturbation theory within the dynamically screened single-particle Green's function approximation, to look at the optoelectronic properties of HAp. These methods are also applied to the calculation of defect levels. We find that the use of a mix of (semi-)local and exact exchange in the exchange-correlation functional brings a drastic improvement to the band structure. Important side effects include improvements in the description of dielectric and optical properties not only involving conduction band (excited) states but also the valence. We find that the highly dispersive conduction band bottom of HAp originates from anti-bonding σ* states along the ⋯OH-OH-⋯ infinite chain, suggesting the formation of a conductive 1D-ice phase. The choice of the exchange-correlation treatment to the calculation of defect levels was also investigated by using the OH-vacancy as a testing model. We find that donor and acceptor transitions obtained within semi-local density functional theory (DFT) differ from those of hybrid-DFT by almost 2 eV. Such a large discrepancy emphasizes the importance of using a high-quality description of the electron-electron interactions in the calculation of electronic and optical transitions of defects in HAp.
羟基磷灰石（HAp）是哺乳动物骨骼和牙齿的重要组成部分，被广泛应用于假体植入物。尽管 HAp 在医学上很重要，但涉及这种材料的一些有前途的应用（例如光催化）取决于我们对其基本性质的了解程度。其中一些性质要么是未知的，要么是不准确的，我们对电子能带结构及其相关性质，包括带隙宽度，都缺乏了解。我们采用了最先进的方法，包括密度泛函理论和基于单粒子格林函数近似的多体微扰理论，来研究 HAp 的光电性质。这些方法也被应用于缺陷能级的计算。我们发现，在交换相关泛函中使用（半）局部和精确交换的混合物，可以极大地改善能带结构。重要的副作用包括对介电和光学性质的描述的改善，不仅涉及导带（激发）态，还涉及价带。我们发现 HAp 高度弥散的导带底部源于 ⋯OH-OH-⋯ 无限链上的反键 σ*态，这表明形成了一个导电的 1D-冰相。我们还通过使用 OH 空位作为测试模型，研究了计算缺陷能级时对交换相关处理的选择。我们发现，在半局域密度泛函理论（DFT）中获得的施主和受主跃迁与混合 DFT 中的跃迁相差近 2 eV。如此大的差异强调了在计算 HAp 中缺陷的电子和光学跃迁时，使用高质量的电子-电子相互作用描述的重要性。
