Renata M. Wentzcovitch

Lamont-Doherty Earth Observatory

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Koichiro Umemoto

Life Science Institute

139

Zhongqing Wu

Center for Excellence in Molecular Cell Science

Gaurav Shukla

Indian Institute of Science Education and Research Kolkata

Yang Sun

Xiamen University

Han Hsu

National Central University

Kai‐Ming Ho

Iowa State University

Cai‐Zhuang Wang

Ames National Laboratory

Stefano de Gironcoli

Scuola Internazionale Superiore di Studi Avanzati

Matteo Cococcioni

University of Pavia

Jun Tsuchiya

Ehime University

Cooperative Institutions

University of Minnesota

Chinese Academy of Sciences

University of Science and Technology of China

Centre National de la Recherche Scientifique

Princeton University

Scuola Internazionale Superiore di Studi Avanzati

Planetary Science Institute

University of Minnesota System

University of California, Berkeley

Peking University

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Post-stishovite transition in hydrous aluminous SiO2

Physics of The Earth and Planetary Interiors (2016)

Koichiro Umemoto Katsuyuki Kawamura Kei Hirose Renata M. Wentzcovitch

Stishovite

Anhydrous

Redistribution

10.1016/j.pepi.2016.03.008

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Citations (28)

PBE-GGA predicts the B8↔B2 phase boundary of FeO at Earth’s core conditions

Proceedings of the National Academy of Sciences (2023)

Zhen Zhang Yang Sun Renata M. Wentzcovitch

FeO is a crucial component of the Earth's core, and its thermodynamic properties are essential to developing more accurate core models. It is also a notorious correlated insulator in the NaCl-type (B1) phase at ambient conditions. It undergoes two polymorphic transitions at 300 K before it becomes metallic in the NiAs-type (B8) structure at ~100 GPa. Although its phase diagram is not fully mapped, it is well established that the B8 phase transforms to the CsCl-type (B2) phase at core pressures and temperatures. Here, we report a successful ab initio calculation of the B8↔B2 phase boundary in FeO at Earth's core pressures. We show that fully anharmonic free energies computed with the Perdew-Burke-Ernzerhof-generalized gradient approximation coupled with thermal electronic excitations reproduce the experimental phase boundary within uncertainties at P > 255 GPa, including the largely negative Clapeyron slope of -52 MPa/K. This study validates the applicability of a standard density functional theory functional to FeO under Earth's core conditions and demonstrates the theoretical framework that enables complex predictive studies of this region.

Phase boundary

Outer core

10.1073/pnas.2304726120

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Influence of the spin crossover in ferropericlase on the lower mantle geotherm

Juan Valencia-Cardona Gaurav Shukla C.-W. Qian Zhiming Wu Renata M. Wentzcovitch

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Quasiharmonic elastic constants corrected for deviatoric thermal stresses

Physical Review B (2008)

Pierre Carrier João F. Justo Renata M. Wentzcovitch

The quasiharmonic approximation (QHA), in its simplest form also called the statically constrained (SC) QHA, has been shown to be a straightforward method to compute thermoelastic properties of crystals. Recently we showed that for noncubic solids SC-QHA calculations develop deviatoric thermal stresses at high temperatures. Relaxation of these stresses leads to a series of corrections to the free energy that may be taken to any desired order, up to self-consistency. Here we show how to correct the elastic constants obtained using the SC-QHA. We exemplify the procedure by correcting to first order the elastic constants of ${\text{MgSiO}}_{3}$ perovskite and ${\text{MgSiO}}_{3}$ postperovskite, the major phases of the Earth's lower mantle. We show that this first-order correction is quite satisfactory for obtaining the aggregated elastic averages of these minerals and their velocities in the lower mantle. This type of correction is also shown to be applicable to experimental measurements of elastic constants in situations where deviatoric stresses can develop, such as in diamond-anvil cells.

Thermoelastic damping

Elasticity

Elastic energy

10.1103/physrevb.78.144302

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Phonon dispersion throughout the iron spin crossover in ferropericlase

Physical review. B./Physical review. B (2020)

Michel L. Marcondes Fawei Zheng Renata M. Wentzcovitch

Ferropericlase (Fp), (Mg$_\mathrm{1-x}$Fe$_\mathrm{x}$)O, is the second most abundant phase in the Earths lower mantle. At relevant pressure-temperature conditions, iron in Fp undergoes a high spin (HS), S=2, to low spin (LS), S=0, state change. The nature of this phenomenon is quite well understood now, but there are still basic questions regarding the structural stability and the existence of soft phonon modes during this iron state change. General theories exist to explain the volume reduction, the significant thermo-elastic anomalies, and the broad nature of this HS-LS crossover. These theories make extensive use of the quasi-harmonic approximation (QHA). Therefore, dynamical and structural stability is essential to their validity. Here, we investigate the vibrational spectrum of Fp throughout this spin-crossover using $\textit{ab initio}$ DFT+Usc calculations. We address vibrational modes associated with isolated and (2nd) nearest neighbor iron ions undergoing the HS-LS state change. As expected, acoustic modes of this solid solution are resilient while optical modes are the most affected. We show that there are no soft phonon modes across this HS-LS crossover, and Fp is dynamically stable at all relevant pressures.

Spin Crossover

10.1103/physrevb.102.104112

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Thermal conductivity from phonon quasiparticles with subminimal mean free path in the MgSiO3 perovskite

Physical review. B./Physical review. B (2017)

Dong‐Bo Zhang Philip B. Allen Tao Sun Renata M. Wentzcovitch

Understanding the lattice thermal conductivity at high temperatures is important for many applications. We characterize phonon quasiparticles numerically through a hybrid approach that combines first-principles molecular dynamics and lattice dynamics. We find no lower-bound limits on phonon mean free paths in the ${\mathrm{MgSiO}}_{3}$ perovskite. This contradicts the widely used minimal mean free path idea. The clear identification of phonon quasiparticles validates the use of a phonon gas model when the phonon mean free paths are shorter than the lattice constants of solids. Using the phonon quasiparticle properties, we have calculated the lattice thermal conductivity of the ${\mathrm{MgSiO}}_{3}$ perovskite. The results are reasonable compared to recent experimental measurements.

Lattice (music)

10.1103/physrevb.96.100302

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Anomalous Pressure-Induced Transition(s) in Ice XI

Physical Review Letters (2004)

Koichiro Umemoto Renata M. Wentzcovitch Stefano Baroni Stefano de Gironcoli

The effects of pressure on the structure of ice XI-an ordered form of the phase of ice Ih, which is known to amorphize under pressure-are investigated theoretically using density-functional theory. We find that pressure induces a mechanical instability, which is initiated by the softening of an acoustic phonon occurring at an incommensurate wavelength, followed by the collapse of the entire acoustic band and by the violation of the Born stability criteria. It is argued that phonon collapse may be a quite general feature of pressure-induced amorphization. The implications of our findings for the amorphization of ice Ih are also discussed.

10.1103/physrevlett.92.105502

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Melting Temperature of Iron Under the Earth's Inner Core Condition from Deep Machine Learning

arXiv (Cornell University) (2024)

Fulun Wu Cai‐Zhuang Wang Kai‐Ming Ho Shunqing Wu Renata M. Wentzcovitch

Constraining the melting temperature of iron under Earth's inner core conditions is crucial for understanding core dynamics and planetary evolution. Here, we develop a deep potential (DP) model for iron that explicitly incorporates electronic entropy contributions governing thermodynamics under Earth's core conditions. Extensive benchmarking demonstrates the DP's high fidelity across relevant iron phases and extreme pressure and temperature conditions. Through thermodynamic integration and direct solid-liquid coexistence simulations, the DP predicts melting temperatures for iron at the inner core boundary, consistent with previous \textit{ab initio} results. This resolves the previous discrepancy of iron's melting temperature at ICB between the DP model and \textit{ab initio} calculation and suggests the crucial contribution of electronic entropy. Our work provides insights into machine learning melting behavior of iron under core conditions and provides the basis for future development of binary or ternary DP models for iron and other elements in the core.

Core temperature

10.48550/arxiv.2404.17852

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Phonon Quasi-Particles and Anharmonic Free Energy in Complex Systems

Bulletin of the American Physical Society (2014)

Dong‐Bo Zhang Tao Sun Renata M. Wentzcovitch

Source

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Anharmonic thermodynamic properties and phase boundary across the post-perovskite transition in MgSiO$_3$

arXiv (Cornell University) (2022)

Zhen Zhang Renata M. Wentzcovitch

To address the effects of lattice anharmonicity across the perovskite to post-perovskite transition in MgSiO$_3$, we conduct calculations using the phonon quasiparticle (PHQ) approach. The PHQ is based on \textit{ab initio} molecular dynamics and, in principle, captures full anharmonicity. Free energies in the thermodynamic limit ($N \rightarrow \infty$) are computed using temperature-dependent quasiparticle dispersions within the phonon gas model. Systematic results on anharmonic thermodynamic properties and phase boundary are reported. Both the local density approximation (LDA) and the generalized gradient approximation (GGA) calculations are performed to provide confident constraints on these properties. Anharmonic effects are demonstrated by comparing results with those obtained using the quasiharmonic approximation (QHA). The inadequacy of the QHA is indicated by its overestimation of thermal expansivity and thermodynamic Grüneisen parameter and its converged isochoric heat capacity in the high-temperature limit. The PHQ phase boundary has a Clapeyron slope ($dP/dT$) that increases with temperature. This result contrasts with the nearly zero curvature of the QHA phase boundary. Anharmonicity bends the phase boundary to lower temperatures at high pressures. Implications for the double-crossing of the phase boundary by the mantle geotherm are discussed.

Supercooling

Phase boundary

10.48550/arxiv.2204.13159

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Citations (2)