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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
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42
Sep 22, 2013
09/13
by
Han Hsu; Peter Blaha; Matteo Cococcioni; Renata M. Wentzcovitch
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Using density functional theory plus Hubbard $U$ calculations, we show that the ground state of (Mg,Fe)(Si,Fe)O$_3$ perovskite, a major mineral phase in the Earth's lower mantle, has high-spin ferric iron ($S=5/2$) at both the dodecahedral (A) and octahedral (B) site. As the pressure increases, the B-site iron undergoes a spin-state crossover to the low-spin state ($S=1/2$), while the A-site iron remains in the high-spin state. Our calculation shows that the B-site spin-state crossover in the...
Source: http://arxiv.org/abs/1101.3819v2
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43
Jul 20, 2013
07/13
by
Han Hsu; Peter Blaha; Renata M. Wentzcovitch
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With local density approximation + Hubbard $U$ (LDA+$U$) calculations, we show that the ferromagnetic (FM) insulating state observed in tensile-strained LaCoO$_3$ epitaxial thin films is most likely a mixture of low-spin (LS) and high-spin (HS) Co, namely, a HS/LS mixture state. Compared with other FM states, including the intermediate-spin (IS) state (\textit{metallic} within LDA+$U$), which consists of IS Co only, and the insulating IS/LS mixture state, the HS/LS state is the most favorable...
Source: http://arxiv.org/abs/1203.1861v1
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6.0
Jun 30, 2018
06/18
by
Han Hsu; Renata M. Wentzcovitch
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Spin crossover of iron is of central importance in solid Earth geophysics. It impacts all physical properties of minerals that altogether constitute $\sim 95$ vol\% of the Earth's lower mantle: ferropericlase [(Mg,Fe)O] and Fe-bearing magnesium silicate (MgSiO$_3$) perovskite. Despite great strides made in the past decade, the existence of intermediate-spin (IS) state in ferrous iron (Fe$^{2+}$) (with total electron spin $S=1$) and its possible role in the pressure-induced spin crossover in...
Topics: Physics, Geophysics, Strongly Correlated Electrons, Materials Science, Condensed Matter
Source: http://arxiv.org/abs/1410.7200
