Advanced Topics on Condensed Matter Physics
Department of Physics, NCU
Applications of first-principles calculations in spin-crossover minerals:
(Mg,Fe)CO3 ferromagnesite and the NAL phase
Speaker
Prof. Han Hsu
Department of Physics, National Central University
Date 2016/10/20 (Thur)
Time 14.00
Place S4-625
Spin crossover (SCO) in iron-bearing minerals has attracted tremendous attention in recent years, as SCO usually leads to anomalous changes of the elastic, conducting, and thermodynamic properties of these minerals. Possible geophysical effects of SCO have been anticipated as well. With the development of the local density approximation + self-consistent Hubbard U (LDA+Usc) method, first-principles calculations have elucidated SCO in many lower-mantle minerals. The success of LDA+Usc lies in its capability to correctly identify the ground state in a wide pressure range and to accurately determine the mechanism of SCO, including the transition pressure PT. In this talk, two recent LDA+Usc studies of SCO minerals are presented: (Mg,Fe)CO3 ferromagnesite [1] and the “new aluminous (NAL) phase” [2]. The former is believed to be the major carbon carrier in the Earth’s lower mantle and play a key role in the deep carbon cycle; the latter is considered as a main host of aluminum in the subducted basalt and may be related to the seismic heterogeneities. For both minerals, the abrupt change of iron quadrupole splitting and the volume/elastic anomalies accompanying the SCO obtained in our calculations are in great agreement with experiments. Our calculations also suggest that the spin transition pressure PT in the NAL phase is not very sensitive to temperature, due to its nearly degenerate low-spin (LS) states, in contrast with (Mg,Fe)O ferropericlase and (Mg,Fe)CO3 ferromagnesite, in which PT significantly increases with temperature. By examining the overall performance of the LDA+Usc method in ferromagnesite and the NAL phase, along with our previous calculations for ferropericlase and Fe-bearing MgSiO3 bridgmanite [3-5], we have established LDA+Usc a highly reliable method to study iron-bearing minerals and related materials under high pressure.
[1] H. Hsu and S.-C. Huang, Phys. Rev. B 94, 060404(R) (2016).
[2] H. Hsu, in preparation.
[3] H. Hsu and R. M. Wentzcovitch, Phys. Rev. B 90, 195205 (2014).
[4] H. Hsu et al., Earth Planet. Sci. Lett. 359-360, 34 (2012).
[5] H. Hsu et al., Phys. Rev. Lett. 106, 118501 (2011).