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Alchemical screening of ionic crystals

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Solovyeva Alisa, von Lilienfeld O. Anatole,
Project From atomistic exploration of chemical compound space towards bio-molecular design: Quantum mechanical rational compound design (QM-RCD)
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Original article (peer-reviewed)

Journal Phys Chem Chem Phys
Volume (Issue) 18
Page(s) 31078
Title of proceedings Phys Chem Chem Phys
DOI 10.1039/c6cp04258a

Abstract

We introduce alchemical perturbations as a rapid and accurate tool to estimate fundamental structural and energetic properties in pure and mixed ionic crystals. We investigated formation energies, lattice constants, and bulk moduli for all sixteen iso-valence-electron combinations of pure pristine alkali halides involving elements Me ∈ {Na, K, Rb, Cs} and X ∈ {F, Cl, Br, I}. For rock salt, zinc-blende, and cesium chloride symmetry, alchemical Hellmann–Feynman derivatives, evaluated along lattice scans of sixteen reference crystals, have been obtained for coupling to all respective 16 × 15 target crystals. Mean absolute errors (MAEs) are on par with the density functional theory level of accuracy for energies and bulk moduli. The predicted lattice constants are less accurate but reproduce qualitative trends. The reference salt NaCl affords the most accurate alchemical estimates of relative energies (MAE < 40 meV per atom). The best predictions of lattice constants are based on NaF as a reference salt (MAE < 0.5 Å), accounting only for qualitative trends. The best reference salt for the prediction of bulk moduli is CsCl (MAE < 0.4 × 1011 dynes cm−2). The alchemical predictions distinguish competing rock salt and cesium chloride phases in binary and ternary solid mixtures with CsCl. Using pure RbI as a reference salt, they reproduce the reversal of the rock salt/cesium chloride stability trend for binary MeX1−xCsClx as well as for ternary MeX0.5−0.5x(Me′Y)0.5−0.5xCsClx mixtures.
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