Theoretical Study of Properties of Goethite (伪-FeOOH) at Ambient and High-Pressure Conditions

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• 作者：Daniel Tunega
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：March 22, 2012
• 年：2012
• 卷：116
• 期：11
• 页码：6703-6713
• 全文大小：503K
• 年卷期：v.116,no.11(March 22, 2012)
• ISSN：1932-7455

文摘

Magnetic, electronic, structural, vibrational, and mechanical properties of mineral goethite (伪-FeOOH) at ambient conditions and their dependence on isostatic volume compression (corresponding pressure range 0鈥?0 GPa) have been studied by means of spin-polarized density functional theory (spDFT), modified spDFT+U method, which includes a Hubbard-type on-site repulsion term U, and hybrid DFT functional MSE06. The antiferromagnetic high spin ground state has been confirmed as the most stable at low-pressure conditions. Calculated Fe magnetic moments differ from experiment by about 0.3鈥?.4 渭_B. The antiferromagnetic high spin state is stable over the whole compression range in the spDFT+U and MSE06 calculations. For the spDFT, a collapse from a high spin to low spin state has been induced by compression. In comparison to experiment, the spDFT method strongly underestimates electronic band gap, and the spDFT+U results are in a reasonable agreement (with a difference of 0.1鈥?.5 eV), while the hybrid MSE06 functional gives an overestimated value. The spDFT+U calculated band gap narrows upon increasing volume compression. Structural parameters calculated by all three methods are in very good agreement with experimental data with an error below 1鈥?.5%. The analysis of structural parameters has shown that the compression proceeds mainly through the compression of structural channels containing hydrogen bonds. Very narrow splitting in a range of 20 cm^鈥? has been found for the calculated OH stretching modes. The predicted bulk modulus of 114.3 GPa (spDFT+U) is in accord with an experimental value of 111 GPa. The calculated elastic constants document an anisotropic character of the single crystal structure of goethite. In general, the spDFT+U provides reliable results for all studied properties, while the MSE06 overestimates some of them (e.g., band gap).