npj: 固体稳定性—分解反应DFT预测

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就新材料高通量筛选来说，候选材料是否满足应用要求，其相对于所有竞争化合物的稳定性是一个重要参考条件。尽管稳定性预测与化合物分解焓ΔH_d之间存在密切联系，但新开发的改进密度泛函和/或统计校正方案等方法，主要是针对实测生成焓ΔH_f进行基准测试，并未计算评估化合物分解焓ΔH_d。

来自美国科罗拉多大学的Charles B. Musgrave和Aaron M. Holder领导的团队，通过分析Materials Project数据库中约56,000种化合物相图，按分解反应是否生成元素相，将分解反应分为三种类型：1）仅生成单质相，2）仅生成化合物，3）同时生成单质相和化合物，并对每种反应类型作了量化。他们发现ΔH_f只在极少数情况下（数据库中仅约3%的化合物）才成为稳定性预测所需的定量参数，但ΔH_d却是稳定性预测最相关的量化参数。他们将广义梯度近似（GGA、PBE）和meta-GGA（SCAN）密度函数预测与实测的ΔH_d和ΔH_f进行基准比较，发现在定性和定量上都存在差异。对于仅生成化合物的231种分解反应（类型2），SCAN、PBE与实测结果之间的一致性在~35 meV / atom内。无论选择函数还是元素的参考能量，实验结果和理论结果之间的差异，都是ΔH_d系统地低于ΔH_f。这是因为，应用PBE预测ΔH_f时对化学组成高度敏感，应用PBE +、SCAN和SCAN +预测也有中等程度敏感，但各函数在预测反应类型2的ΔH_d时，对化学组成却不敏感，变化很小。他们的研究表明，由于反应类型2的分解反应在确定固体稳定性方面起主要作用，因此用高通量DFT方法所作的稳定性预测，通常与多种材料的实验结果非常一致。

该文近期发表于npj Computational Materials 5: 4 (2019)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。

The role of decomposition reactions in assessing first-principles predictions of solid stability

Christopher J. Bartel, Alan W. Weimer,Stephan Lany, Charles B. Musgrave & Aaron M. Holder 

The performance of density functional theory approximations for predicting materials thermodynamics is typically assessed by comparing calculated and experimentally determined enthalpies of formation from elemental phases, ΔH_f. However, a compound competes thermodynamically with both other compounds and their constituent elemental forms, and thus, the enthalpies of the decomposition reactions to these competing phases, ΔHd, determine thermodynamic stability. We evaluated the phase diagrams for 56,791 compounds to classify decomposition reactions into three types: 1. those that produce elemental phases, 2. those that produce compounds, and 3. those that produce both. This analysis shows that the decomposition into elemental forms is rarely the competing reaction that determines compound stability and that approximately two-thirds of decomposition reactions involve no elemental phases. Using experimentally reported formation enthalpies for 1012 solid compounds, we assess the accuracy of the generalized gradient approximation (GGA) (PBE) and meta-GGA (SCAN) density functionals for predicting compound stability. For 646 decomposition reactions that are not trivially the formation reaction, PBE (mean absolute difference between theory and experiment (MAD) = 70 meV/atom) and SCAN (MAD = 59 meV/atom) perform similarly, and commonly employed correction schemes using fitted elemental reference energies make only a negligible improvement (~2 meV/atom). Furthermore, for 231 reactions involving only compounds (Type 2), the agreement between SCAN, PBE, and experiment is within ~35 meV/atom and is thus comparable to the magnitude of experimental uncertainty.

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