First-principles predictions of stability are at the heart of most materials-by-design applications, especially those related to high-throughput density functional theory (DFT) calculations as found in open materials databases (e.g., Materials Project). The performance of DFT approximations for predicting materials thermodynamics is typically assessed by comparing calculated and experimentally determined enthalpies of formation from elemental phases, ΔHf. 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, determines thermodynamic stability. We evaluated the phase diagrams for 56,791 compounds (the entire Materials Project database) 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 1,012 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 (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. In culmination, this work demonstrates the critical importance of decomposition enthalpies and provides a quantitative guide to the many researchers using high-throughput density functional theory to predict the stability of new materials.

Decomposition reactions dictate the performance of first-principles predictions of solid-stability

2019 Spring National Meeting

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