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arXiv 2501.04434cond-mat.mtrl-sciphysics.comp-ph
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含钼氧化物中稳定性的异常反转:一个对DFT+U和畸变表现出敏感性的困难案例

Anomalous Reversal of Stability in Mo-containing Oxides: A Difficult Case Exhibiting Sensitivity to DFT+U and Distortion

Tzu-chen Liu, Dale Gaines, Hyungjun Kim, Adolfo Salgado-Casanova, Steven B. Torrisi, Chris Wolverton

AI总结:

本文系统研究了DFT+U中U$_{\ ext{eff}}$取值对含钼氧化物结构稳定性预测的异常反转效应,揭示高U$_{\ ext{eff}}$(约4 eV及以上)会导致能量预测失真,并建议在凸包构建中谨慎评估DFT+U的使用。

摘要:

利用密度泛函理论(DFT)计算准确预测过渡金属氧化物的性质对于能源材料的计算设计至关重要。在这项工作中,我们研究了在层状AMoO$_2$(A = Li, Na, K)和类金红石MoO$_2$中,由施加在Mo d轨道上的DFT+U引起的结构畸变稳定性的异常反转(即畸变结构相对于未畸变结构从能量有利急剧变为不利)。我们强调了不同U$_{\ ext{eff}}$值对结构稳定性、凸包(convex hull)和热力学稳定性预测的显著影响,并指出在这些能量量上偏差可高达100 meV/atom的量级。我们发现稳定性转变与电子局域化和磁行为的变化同时发生。这种异常反转在PBE、r$^2$SCAN泛函以及vdW色散能量修正(PBE+D3)下均持续存在。在含钼氧化物体系中,高U$_{\ ext{eff}}$会导致在人为对称性约束下对物理量和结构弛豫的不准确描述,这一点通过声子能带结构、Heyd-Scuseria-Ernzerhof(HSE06)杂化泛函结果以及与实验结构数据的比较得到了证明。我们得出结论:高U$_{\ ext{eff}}$值(约4 eV及以上,取决于具体结构和组成)可能不适合用于A-Mo-O化学空间中的能量预测。我们的结果表明,将DFT+U应用于凸包构建的常见做法——尤其是使用由拟合得到的高U$_{\ ext{eff}}$值时——应当被仔细评估,以确保基态被正确重现,并充分考虑动力学稳定性和可能的能量有利畸变。

英文摘要:

Accurate predictions of the properties of transition metal oxides using density functional theory (DFT) calculations are essential for the computational design of energy materials. In this work, we investigate the anomalous reversal of the stability of structural distortions (where distorted structures go from being energetically favorable to sharply unfavorable relative to undistorted ones) induced by DFT+U on Mo d-orbitals in layered AMoO$_2$ (A = Li, Na, K) and rutile-like MoO$_2$. We highlight the significant impact of varying U$_{\text{eff}}$ values on the structural stability, convex hull, and thermodynamic stability predictions, noting that deviations can reach up to the order of 100 meV/atom across these energetic quantities. We find the transitions in stability are coincident with changes in the electron localization and magnetic behavior. The anomalous reversal persists across PBE, r$^2$SCAN functionals, and also with vdW-dispersion energy corrections (PBE+D3). In Mo-containing oxide systems, high U$_{\text{eff}}$ leads to inaccurate descriptions of physical quantities and structural relaxations under artificial symmetry constraints, as demonstrated by the phonon band structures, the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional results, and comparisons with experimental structural data. We conclude that high U$_{\text{eff}}$ values (around 4 eV and above, depending on the specific structures and compositions) might be unsuitable for energetic predictions in A-Mo-O chemical spaces. Our results suggest that the common practice of applying DFT+U to convex hull constructions, especially with high U$_{\text{eff}}$ values derived from fittings, should be carefully evaluated to ensure that ground states are correctly reproduced, with careful consideration of dynamic stability and possible energetically favorable distortions.

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