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arXiv 2303.02764cond-mat.mtrl-sci
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基于第一性原理的晶体圆二色性研究

Circular Dichroism of Crystals from First Principles

Christian Multunas, Andrew Grieder, Junqing Xu, Yuan Ping, Ravishankar Sundararaman

AI总结:

本文提出基于DFT和Wannier插值的高效第一性原理计算框架,用于预测晶体圆二色性,揭示了四极矩贡献和各向异性来源,并在二维杂化钙钛矿中验证了方法的准确性与实用性。

摘要:

手性晶体因其高自旋选择性而在自旋电子学技术中展现出广阔前景,这引发了近年来对其自旋光电子学性质的定量表征和第一性原理预测的显著关注。本文中,我们构建了一个用于高效从头计算晶体材料圆二色性(CD)的计算框架。我们利用密度泛函理论(DFT)中轨道角动量和四极矩矩阵元的直接计算以及Wannier插值来计算复杂材料中的CD,从而消除了对能带收敛的需求,并相比先前方法加速了布里渊区收敛。我们发现计算结果与分子和晶体中测得的CD信号高度一致,这些体系复杂程度各异,从小体相原胞到二维杂化钙钛矿,并展示了四极矩贡献对晶体中各向异性CD的重要性。自旋轨道耦合会影响含较重原子晶体的CD,正如预期的那样,但这主要源于电子能量的变化,而非来自自旋矩阵元的直接贡献。我们展示了在二维杂化钙钛矿上预测复杂结构CD的能力,发现了强烈的取向依赖性,并识别出原胞中具有最强CD的本征方向。此外,我们将CD分解为来自无机、有机以及有机-无机混合跃迁的独立贡献,发现手性分子主导CD,而无机晶格在特定方向上以更高频率贡献。这种在晶体CD预测中前所未有的细节水平将促进用于自旋选择性的复杂手性晶体的实验开发。

英文摘要:

Chiral crystals show promise for spintronic technologies on account of their high spin selectivity, which has led to significant recent interest in quantitative characterization and first-principles prediction of their spin-optoelectronics properties. Here, we outline a computational framework for efficient ab-initio calculations of circular dichroism (CD) in crystalline materials. We leverage direct calculations of orbital angular momentum and quadrupole matrix element calculations in density-functional theory (DFT) and Wannier interpolation to calculate CD in complex materials, removing the need for band convergence and accelerating Brillouin-zone convergence compared to prior approaches. We find strong agreement with measured CD signals in molecules and crystals ranging in complexity from small bulk unit cells to 2D hybrid perovskites, and show the importance of the quadrupole contribution to the anisotropic CD in crystals. Spin-orbit coupling affects the CD of crystals with heavier atoms, as expected, but this is primarily due to changes in the electronic energies, rather than due to direct contributions from the spin matrix elements. We showcase the capability to predict CD for complex structures on a 2D hybrid perovskite, finding strong orientation dependence and identifying the eigen-directions of the unit cell with the strongest CD. We additionally decompose CD into separate contributions from inorganic, organic, and mixed organic-inorganic transitions, finding the chiral molecules to dominate the CD, with the inorganic lattice contributing at higher frequencies in specific directions. This unprecedented level of detail in CD predictions in crystals will facilitate experimental development of complex chiral crystals for spin selectivity.

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