Quantum Monte Carlo computations of phase stability, equations of state, and elasticity of high-pressure silica
| Autor: | Burkhard Militzer, John W. Wilkins, Ronald E. Cohen, Kevin P. Driver, Richard J. Needs, Towler, Zhigang Wu, Pablo López Ríos |
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| Rok vydání: | 2010 |
| Předmět: |
Physics
Multidisciplinary 010504 meteorology & atmospheric sciences Condensed matter physics Phonon Quantum Monte Carlo Classification of discontinuities 01 natural sciences Physics::Geophysics symbols.namesake Physical Sciences 0103 physical sciences Thermal symbols First principle Density functional theory Statistical physics 010306 general physics Schrödinger's cat 0105 earth and related environmental sciences Stishovite |
| Zdroj: | Proceedings of the National Academy of Sciences. 107:9519-9524 |
| ISSN: | 1091-6490 0027-8424 |
| Popis: | Silica (SiO 2 ) 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 Schrödinger’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 α -PbO 2 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. |
| Databáze: | OpenAIRE |
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