Bae Soungmin, Egawa Noriyuki, Raebiger Hannes
Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan.
Department of Physics, Yokohama National University, Yokohama, 240-8501, Japan.
Sci Rep. 2025 Mar 4;15(1):7567. doi: 10.1038/s41598-025-92069-7.
The Strongly Constrained and Appropriately Normed (SCAN) meta-GGA (generalized gradient approximation) density functional and its regularized derivatives (e.g., SCAN and rSCAN) have been proposed as a post-standard exchange-correlation functional, and are widely believed to replace conventional GGA functionals (e.g. PBE-GGA) owing to greatly improved electronic structures of strongly correlated systems and overall accuracy of total energies. While these improvements have been widely demonstrated for various systems, we report a significant failure of SCAN functionals related to erroneous stability of multivalent states of copper: SCAN and its derivatives (rSCAN) critically fail to predict the relative stability of copper in oxidation states Cu(d) and Cu(d), excessively stabilizing Cu over Cu, which leads to wrong relative stability of CuO and CuO. This spurious bias also results in unphysical oxygen defect structures of YBaCuO for small δ. While the PBE-GGA functional can be fixed with a simple Hubbard-U correction (PBE + U) to predict both the spectral and thermochemical properties of copper compounds correctly, this is shown to not be the case for SCAN functionals. Our work advocates careful consideration of SCAN meta-GGA functionals when they are applied for cuprate superconductors, catalysis, and defect studies of copper compounds.
强约束与适当归一化（SCAN）元广义梯度近似（meta - GGA）密度泛函及其正则化衍生物（如SCAN和rSCAN）已被提议作为一种后标准交换关联泛函，并且由于其极大地改善了强关联体系的电子结构以及总能的整体精度，人们普遍认为它将取代传统的GGA泛函（如PBE - GGA）。虽然这些改进已在各种体系中得到广泛证明，但我们报告了SCAN泛函在与铜多价态的错误稳定性相关方面的一个重大失败：SCAN及其衍生物（rSCAN）严重无法预测铜在氧化态Cu(Ⅰ)和Cu(Ⅱ)下的相对稳定性，过度稳定了Cu(Ⅰ)而不是Cu(Ⅱ)，这导致了Cu₂O和CuO的相对稳定性错误。这种虚假偏差还导致了小δ值下YBa₂Cu₃O₆₊δ的非物理氧缺陷结构。虽然PBE - GGA泛函可以通过简单的哈伯德U校正（PBE + U）来修正，从而正确预测铜化合物的光谱和热化学性质，但对于SCAN泛函而言并非如此。我们的工作倡导在将SCAN元GGA泛函应用于铜酸盐超导体、催化以及铜化合物的缺陷研究时要谨慎考虑。
