The Open Quantum Materials Database (OQMD): assessing the accuracy of DFT formation energies

Abstract

The Open Quantum Materials Database (OQMD) is a high-throughput database currently consisting of nearly 300,000 density functional theory (DFT) total energy calculations of compounds from the Inorganic Crystal Structure Database (ICSD) and decorations of commonly occurring crystal structures. To maximise the impact of these data, the entire database is being made available, without restrictions, at www.oqmd.org/download. In this paper, we outline the structure and contents of the database, and then use it to evaluate the accuracy of the calculations therein by comparing DFT predictions with experimental measurements for the stability of all elemental ground-state structures and 1,670 experimental formation energies of compounds. This represents the largest comparison between DFT and experimental formation energies to date. The apparent mean absolute error between experimental measurements and our calculations is 0.096 eV/atom. In order to estimate how much error to attribute to the DFT calculations, we also examine deviation between different experimental measurements themselves where multiple sources are available, and find a surprisingly large mean absolute error of 0.082 eV/atom. Hence, we suggest that a significant fraction of the error between DFT and experimental formation energies may be attributed to experimental uncertainties. Finally, we evaluate the stability of compounds in the OQMD (including compounds obtained from the ICSD as well as hypothetical structures), which allows us to predict the existence of~3,200 new compounds that have not been experimentally characterised and uncover trends in material discovery, based on historical data available within the ICSD.

Can artificial intelligence create the next wonder material?

“…It turns out that the difference between good glass formers and bad ones depends on the number and energies of unstable crystal structures that 'compete' with the ground state while the alloy cools down 10 . Wolverton's OQMD includes around 400,000 hypothetical materials, calculated by taking a list of crystal structures commonly observed in nature and 'decorating' them with elements chosen from almost every part of the periodic table 9 . It has a particularly wide coverage of perovskites -crystals that often display attractive properties such as superconductivity and that are being developed for use in solar cells as microelectronics.…”

Error estimates for density-functional theory predictions of surface energy and work function

“…This is not only true for the quantities discussed in this work. Recently, Kirklin et al [66] concluded that the mean absolute error on experimental formation energies was of comparable size (0.082 eV/atom) to the average absolute difference between DFT and experiment (0.096 eV/atom).…”

A fingerprint based metric for measuring similarities of crystalline structures

“…On one hand, databases of materials have been created containing structural information of both experimental and theoretical compounds from highthroughput calculations, which are the basis for data-mining techniques in materials discovery projects. [1][2][3][4][5][6][7] On the other hand, ab initio structure predictions [8][9][10][11][12][13][14][15] can produce a huge number of new structures that have either not yet been found experimentally or are metastable. [16][17][18][19][20][21] In both cases, it is essential to quantify similarities and dissimilarities between structures in the data sets, requiring a configurational distance that satisfies the properties of a metric.…”