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J Chem Theory Comput. 2016 Oct 11;12(10):5132-5144. Epub 2016 Sep 3.

When Density Functional Approximations Meet Iron Oxides.

Meng Y1,2,3, Liu XW1,2,3, Huo CF2, Guo WP2, Cao DB1,2, Peng Q4, Dearden A5, Gonze X6, Yang Y1,2, Wang J1, Jiao H1,7, Li Y1,2, Wen XD1,2.

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State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences , Taiyuan 030001, P. R. China.
National Energy Center for Coal to Clean Fuels, Synfuels China Co., Ltd. , Huairou District, Beijing 101400, P. R. China.
University of Chinese Academy of Sciences , No. 19A Yuquan Road, Beijing 100049, P. R. China.
Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute , Troy, New York 12180, United States.
Department of Physics, Berea College , Berea, Kentucky 40403, United States.
Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain , Louvain-la-Neuve, Belgium.
Leibniz-Institut für Katalyse e.V., Universität Rostock , Albert-Einstein Strasse 29a, 18059 Rostock, Germany.


Three density functional approximations (DFAs), PBE, PBE+U, and Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE), were employed to investigate the geometric, electronic, magnetic, and thermodynamic properties of four iron oxides, namely, α-FeOOH, α-Fe2O3, Fe3O4, and FeO. Comparing our calculated results with available experimental data, we found that HSE (a = 0.15) (containing 15% "screened" Hartree-Fock exchange) can provide reliable values of lattice constants, Fe magnetic moments, band gaps, and formation energies of all four iron oxides, while standard HSE (a = 0.25) seriously overestimates the band gaps and formation energies. For PBE+U, a suitable U value can give quite good results for the electronic properties of each iron oxide, but it is challenging to accurately get other properties of the four iron oxides using the same U value. Subsequently, we calculated the Gibbs free energies of transformation reactions among iron oxides using the HSE (a = 0.15) functional and plotted the equilibrium phase diagrams of the iron oxide system under various conditions, which provide reliable theoretical insight into the phase transformations of iron oxides.


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