考虑多体效应的MgO光学和X射线吸收谱的理论描述
Theoretical description of optical and X-ray absorption spectra of MgO including many-body effects
摘要：
本文采用密度泛函理论和多体微扰理论计算了宽带隙氧化物MgO的光学和X射线吸收谱。我们对电子结构的全面研究表明，虽然与实验值（7.7 eV）相比，交换相关功能PBEsol（4.58 eV）和混合功能HSE 06（6.58 eV）的带隙被低估，但当考虑准粒子修正时，它显着改善（7.52 eV）甚至过度补偿（8.53 eV）。通过求解Bethe-Salpeter方程（BSE）包含激子效应，得到与实验非常一致的光谱。O和Mg的K边吸收光谱也观察到良好的一致性，表明MBPT内的电子-空穴相互作用的重要性。从能带结构上的BSE本征向量的电子-空穴耦合系数的投影允许我们确定突出峰的起源并识别相关贡献的轨道特征。光谱的最低能量激子波函数的实空间投影表明Wannier-Mott型，而在O K边缘的第一激子更本地化。
英文摘要：
Here we report the optical and x-ray absorption (XAS) spectra of the wide-band-gap oxide MgO using density functional theory (DFT) and many-body perturbation theory (MBPT). Our comprehensive study of the electronic structure shows that while the band gap is underestimated with the exchange-correlation functional PBEsol (4.58 eV) and the hybrid functional HSE06 (6.58 eV) compared to the experimental value (7.7 eV), it is significantly improved (7.52 eV) and even overcompensated (8.53 eV) when quasiparticle corrections are considered. Inclusion of excitonic effects by solving the Bethe-Salpeter equation (BSE) yields the optical spectrum in excellent agreement with experiment. Excellent agreement is observed also for the O and Mg K-edge absorption spectra, demonstrating the importance of the electron-hole interaction within MBPT. Projection of the electron-hole coupling coefficients from the BSE eigenvectors on the band structure allows us to determine the origin of prominent peaks and identify the orbital character of the relevant contributions. The real space projection of the lowest energy exciton wavefunction of the optical spectrum indicates a Wannier-Mott type, whereas the first exciton in the O K-edge is more localized.
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