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14
Jun 27, 2018
06/18
by
Gaurav Shukla; Mehmet Topsakal; Renata M. Wentzcovitch
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MgGeO$_3$-perovskite is known to be a low-pressure analog of MgSiO$_3$-perovskite in many respects, but especially in regard to the post-perovskite transition. As such, investigation of spin state changes in Fe-bearing MgGeO$_3$ might help to clarify some aspects of this type of state change in Fe-bearing MgSiO$_3$. Using DFT+U calculations, we have investigated pressure induced spin state changes in Fe$^{2+}$ and Fe$^{3+}$ in MgGeO$_3$ perovskite and post-perovskite. Owing to the relatively...
Topics: Condensed Matter, Materials Science
Source: http://arxiv.org/abs/1503.07194
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8.0
Jun 29, 2018
06/18
by
Gaurav Shukla; Renata M. Wentzcovitch
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The spin crossover of iron in Fe$^{3+}$-bearing bridgmanite, the most abundant mineral of the Earth's lower mantle, is by now a well-established phenomenon, though several aspects of this crossover remain unclear. Here we investigate effects of disorder, iron concentration, and temperature on this crossover using ab initio LDA + U$_{sc}$ calculations. The effect of concentration and disorder are addressed using complete statistical samplings of coupled substituted configurations in super-cells...
Topics: Materials Science, Condensed Matter, Strongly Correlated Electrons
Source: http://arxiv.org/abs/1603.08947
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3.0
Jun 29, 2018
06/18
by
Gaurav Shukla; Matteo Cococcioni; Renata M. Wentzcovitch
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We report \textit{ab initio} (LDA + U$_{sc}$) calculations of thermoelastic properties of ferric iron (Fe$^{3+}$)- and aluminum (Al)-bearing bridgmanite (MgSiO$_3$ perovskite), the main Earth forming phase, at relevant pressure and temperature conditions and compositions. Three coupled substitutions, namely, [Al]$_{Mg}$-[Al]$_{Si}$, [Fe$^{3+}$]$_{Mg}$-[Fe$^{3+}$]$_{Si}$, and [Fe$^{3+}$]$_{Mg}$-[Al]$_{Si}$ have been investigated. Aggregate elastic moduli and sound velocities are successfully...
Topics: Materials Science, Condensed Matter, Strongly Correlated Electrons
Source: http://arxiv.org/abs/1603.08899
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13
Jun 27, 2018
06/18
by
Gaurav Shukla; Zhongqing Wu; Han Hsu; Andrea Floris; Matteo Cococcioni; Renata M. Wentzcovitch
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We present LDA+U calculations of high temperature elastic properties of bridgmanite with composition (Mg$_{(1-x)}$Fe$_{x}^{2+}$)SiO$_3$ for $0\le{x}\le0.125$. Results of elastic moduli and acoustic velocities for the Mg-end member (x=0) agree very well with the latest high pressure and high temperature experimental measurements. In the iron-bearing system, we focus particularly on the change in thermoelastic parameters across the state change that occurs in ferrous iron above $\sim$30 GPa,...
Topics: Condensed Matter, Materials Science
Source: http://arxiv.org/abs/1503.05983
