Quantum Monte Carlo computations of phase stability, equations of state, and elasticity of high-pressure silica

被引:46
作者
Driver, K. P. [1 ,2 ]
Cohen, R. E. [2 ]
Wu, Zhigang [3 ]
Militzer, B. [2 ,4 ,5 ]
Rios, P. Lopez [6 ]
Towler, M. D. [6 ]
Needs, R. J. [6 ]
Wilkins, J. W. [1 ]
机构
[1] Ohio State Univ, Dept Phys, Columbus, OH 43210 USA
[2] Carnegie Inst Sci, Geophys Lab, Washington, DC 20015 USA
[3] Colorado Sch Mines, Dept Phys, Golden, CO 80401 USA
[4] Univ Calif Berkeley, Dept Earth & Planetary Sci, Berkeley, CA 94720 USA
[5] Univ Calif Berkeley, Dept Astron, Berkeley, CA 94720 USA
[6] Univ Cambridge, Cavendish Lab, Condensed Matter Theory Grp, Cambridge CB3 0HE, England
基金
英国工程与自然科学研究理事会; 美国国家科学基金会;
关键词
first principles computations; lower mantle; thermal properties; LOWER-MANTLE PRESSURES; POST-PEROVSKITE; AB-INITIO; STISHOVITE; DENSITY; SIO2; TRANSFORMATIONS; TEMPERATURE; TRANSITION; CHEMISTRY;
D O I
10.1073/pnas.0912130107
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
Silica (SiO2) is an abundant component of the Earth whose crystalline polymorphs play key roles in its structure and dynamics. First principle density functional theory (DFT) methods have often been used to accurately predict properties of silicates, but fundamental failures occur. Such failures occur even in silica, the simplest silicate, and understanding pure silica is a prerequisite to understanding the rocky part of the Earth. Here, we study silica with quantum Monte Carlo (QMC), which until now was not computationally possible for such complex materials, and find that QMC overcomes the failures of DFT. QMC is a benchmark method that does not rely on density functionals but rather explicitly treats the electrons and their interactions via a stochastic solution of Schrodinger's equation. Using ground-state QMC plus phonons within the quasiharmonic approximation of density functional perturbation theory, we obtain the thermal pressure and equations of state of silica phases up to Earth's core-mantle boundary. Our results provide the best constrained equations of state and phase boundaries available for silica. QMC indicates a transition to the dense alpha-PbO2 structure above the core-insulating D '' layer, but the absence of a seismic signature suggests the transition does not contribute significantly to global seismic discontinuities in the lower mantle. However, the transition could still provide seismic signals from deeply subducted oceanic crust. We also find an accurate shear elastic constant for stishovite and its geophysically important softening with pressure.
引用
收藏
页码:9519 / 9524
页数:6
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