arXiv subjects

Renata M. Wentzcovitch

Publications and source records attributed to Renata M. Wentzcovitch.

At least 19 recordsLinked to original sources

arXiv2026

Assessing foundational atomistic models for iron alloys under Earth's core conditions

We assess the capability of recently developed foundational atomistic models (FAMs) to simulate iron alloys under the extreme pressures and temperatures of Earth's core. Static equations of state for hexagonal close-packed (hcp) and body-centered cubic (bcc) iron, computed using 17 FAMs, are benchmarked against ab initio calculations. Two representative models, MatterSim and MACE, are further evaluated for their ability to reproduce phonon spectra, liquid structure, and melting relations of iron at core conditions. While both models capture several key properties, MACE substantially overestimates the stability of bcc iron and fails to correctly describe the stability of hcp iron. Their performance is also examined for binary liquids, superionic phases, and a seven-component Fe-Ni-Si-S-O-H-C liquid. Although these FAMs were not explicitly trained on data from core conditions, they can reproduce several structural and dynamical properties across a wide range of compositions. However, none of the tested models consistently reproduces all first-principles benchmarks. By analyzing the origins of these discrepancies, we identify several limitations of current FAMs, particularly the lack of an explicit treatment of thermal electronic excitations, which significantly affect phase stability and thermodynamic properties under core conditions. We further discuss directions for improving FAMs to enable predictive simulations of core-forming materials under extreme conditions.

physics.geo-ph↗

arXiv2026

Insights into the long-standing controversy over sound velocities in lizardite

Serpentine minerals are abundant H-bearing phases in the upper mantle and play a central role in water transport in subduction zones. Lizardite is the low-temperature polymorph expected in cold slabs and shallow serpentinized mantle. Using an ab initio thermoelastic framework combining density-functional theory with the r2SCAN meta-GGA and the quasiharmonic approximation, we calculate its compression curve, elastic tensor, and acoustic velocities at 300 K. r2SCAN reproduces the measured compression curve and equilibrium volume to within 0.2%. Weak interlayer hydrogen bonding gives rise to pronounced axial softening, with $C_{33} \simeq 0.21C_{11}$ and $C_{44} \simeq 0.13C_{66}$ at 0 GPa. Solving the Christoffel equation over all propagation directions, we construct the velocity density of states (VelDOS), which reveals a high density of slow acoustic modes and other directional features obscured by Voigt-Reuss-Hill (VRH) aggregate averages. Reported experimental velocities preferentially sample the slower portion of this distribution rather than clustering near the VRH values, a correspondence consistent with subtle crystallographic texture or preferential orientation not resolved experimentally. Thus, the appropriate seismic-velocity endmember for lizardite depends on its orientational state, and reliance on VRH velocities alone may lead to overestimation of the degree of serpentinization when seismic observations preferentially sample slow crystallographic directions. Direction-resolved single-crystal measurements and aggregate measurements with independently quantified texture would provide direct tests of this interpretation.

cond-mat.mtrl-sci↗

arXiv2026

LitCurate: A Configuration-Driven AI-Assisted Framework for Scientific Database Construction with an Application to Lower-Mantle Equation-of-State Data

The growing scientific literature contains decades of experimental and computational results that could support data-driven and physics-based modeling, yet much of this infor- mation remains locked in publications and is not readily usable for large-scale analysis or sci- entific software. Building structured databases from the literature is particularly challenging whenrelevantstudiesmustfirstbediscoveredamonglargecollectionsofpapersandreported quantities must be extracted with enough scientific context to remain usable. We present LitCurate, an open-source framework for building scientific databases from the literature using large language models within an auditable, stage-wise curation workflow. LitCurate integratesliteraturediscovery, relevancescreening, full-textprocessing, andstructuredinfor- mation extraction while retaining intermediate results and provenance, allowing researchers to inspect and revise individual stages rather than treating automated curation as a black- box process. We apply LitCurate to construct an equation-of-state database of lower-mantle and lower-mantle-relevant high-pressure mineral phases from experimental and theoretical studies, comprising 1,334 entries from 205 papers. The resulting dataset links reported equation-of-state parameters to mineral phases, compositions, equation formulations, meth- ods, and parameter constraints, and labels values as source-reported or citation-reported when provenance can be determined. The records are available through a searchable web application. By connecting scientific literature to traceable, machine-readable data, LitCu- rate provides a reusable approach for transforming accumulated literature into resources for scientific analysis and computational modeling.

cs.IR↗

arXiv2026

Alchemical thermodynamic integration for ab initio free-energy calculations in solutions

We develop an alchemical thermodynamic integration scheme that couples ab initio force calculators on the fly during Monte Carlo and molecular dynamics simulations. The implementation is validated against existing hybrid-Hamiltonian approaches. The scheme yields ab initio free energies of high-pressure Fe-Ni and ambient Li-Na liquid solutions that agree with previous calculations and reproduce the experimentally observed Li-Na miscibility gap. The code has an efficiency comparable to standard ab initio molecular dynamics. These results establish this scheme as a practical alchemical-integration framework for first-principles free-energy calculations in solutions.

cond-mat.mtrl-sci↗

arXiv2026

Radial gradient of superionic hydrogen in Earth's inner core

Hydrogen is considered a key light element in Earth's core, yet the thermodynamics of its superionic phase and its distribution in the inner core remain unclear. Here, we compute ab initio Gibbs free energies for liquid and superionic hcp and bcc Fe-H phases and construct the superionic-liquid phase diagram over pressure-temperature conditions relevant to the Earth's inner core. We find that phase diagrams at different inner-core pressures collapse when temperatures are scaled by the melting temperature of pure iron, indicating that solid-liquid partitioning is controlled primarily by a reduced temperature relative to iron melting and is weakly sensitive to pressure. This scaling relation further reconciles previously reported discrepancies in partition coefficients among theoretical studies and yields good agreement with available experimental data at low pressures. By applying thermochemical constraints, our free-energy results reveal a radial hydrogen gradient within the inner core. These results demonstrate that compositional gradients of superionic hydrogen in the inner core emerge naturally from equilibrium thermodynamics and suggest a general mechanism governing the depth-dependent distribution of light elements within Earth's inner core.

physics.geo-ph↗

arXiv2026

Novel phases in the Fe-Si-O system at terapascal pressures

The Fe-Si-O ternary system, central to modeling the interiors of terrestrial planets, remains poorly constrained at Terapascal (TPa) pressures characteristic of super-Earth mantles. Using a combination of crystal-structure prediction and ab initio calculations, we identify three ternary compounds stable near 1 TPa: P3 FeSiO4, P3 Fe4Si5O18, and P-3 FeSi2O6. The first two phases are thermodynamically stable at low temperatures, whereas P-3 FeSi2O6 becomes favored above approximately 2000 K. All three are metallic, paramagnetic, and adopt pseudo-binary arrangements derived from the FeO2 and SiO2 end-member structures. Their crystal structures emerge through substitutions of Fe for Si in Fe2P-type SiO2 or of Si for Fe in Pnma-type FeO2, the stable elemental oxides at ~1 TPa. This structural continuity suggests that Fe preferentially substitutes for Si in the canonical Mg-silicates expected at TPa pressures. Notably, these new pseudo-binaries accommodate Fe in six- and nine-fold coordination, in contrast to the eight-fold cubic coordination found in FeO at similar pressures. The thermodynamic conditions under which these phases form from FeO2 and SiO2 mixtures are clarified through quasi-harmonic free-energy calculations. These phases imply a fundamentally different pattern of Fe incorporation into Mg-silicates at TPa pressures compared with that inferred for Earth's mantle, i.e., mainly [Fe]Mg. Their stability may trigger silicate dissociation into oxides ((Mg,Fe)2(Si,Fe)O4 -> 2(Mg,Fe)O + (Si,Fe)O2) at pressures below ~3 TPa, as expected in the Mg-Si-O system, with the extent of dissociation governed by iron content.

cond-mat.mtrl-sci↗

arXiv2025

Ab initio superionic-liquid phase diagram of Fe1-xOx under Earth's inner core conditions

The superionic state is a phase of matter in which liquid-like ionic mobility coexists with a solid crystalline lattice. Recently identified in Earth's inner core (IC), this state has attracted considerable attention for its unique kinetic behavior and geophysical implications. However, the ab initio phase diagram describing the equilibrium between the superionic phase and the liquid solution under core conditions remains largely unexplored. Here, we present a thermodynamic approach to compute the Gibbs free energy and construct the ab initio superionic-liquid phase diagram for the Fe1-xOx system under IC conditions. We find that oxygen forms superionic states in both hcp and bcc Fe phases, with a pronounced influence on cooperative diffusion of iron in the bcc lattice. The stability fields of these superionic phases are sensitive to oxygen stoichiometry. The presence of superionic states leads to a higher oxygen concentration in the IC than previously estimated. Our work establishes a framework for investigating superionic-liquid equilibria under extreme conditions.

physics.geo-ph↗

arXiv2025

Tetragonal Fe2O: the stable iron oxide at Earth's core conditions

The Fe-O system is fundamental to understanding the composition and properties of the Earth's core. Recent studies have suggested the possible existence of stable, iron-rich FenO compounds at around 215 GPa. Here, we performed crystal-structure searches and fully anharmonic free-energy calculations to investigate the Fe-FeO system under inner-core conditions. We identified Fe2O as a stable phase and constructed its high P-T phase diagram. Fe2O undergoes a hexagonal-to-tetragonal transition with increasing pressure and temperature. It remains thermodynamically stable against decomposition into Fe and FeO from 200 to 400 GPa and at high temperatures. Although oxygen has been considered nearly absent in the inner core due to its limited solubility, these results suggest that oxygen can, in fact, be incorporated into the solid inner core in the form of an Fe+Fe2O mixture, and can match PREM densities for 53 mol% Fe2O. Our work has the potential to lead to a significant revision of the current understanding of the core's structure and composition.

cond-mat.mtrl-sci↗

arXiv2025

The Fe-Ni phase diagram and the Earth's inner core structure

The Fe-Ni alloy is believed to be the main component of Earth's core. Yet, a comprehensive understanding of phase equilibria near the melting point of this alloy under core conditions is still lacking, leaving the effect of nickel inconclusive. Using ab initio simulations, we computed Gibbs free energy and phase diagram for liquid and solid solutions of the Fe-Ni alloy under conditions close to the inner core, considering inner-shell electron contributions and non-ideal mixing effects. The Fe-Ni phase diagram provides crucial insights for understanding previous experimental observations and crystallization simulations of the Fe-Ni alloy under core conditions. It also presents new scenarios for inner core structures, suggesting bcc-liquid coexistence at the inner core boundary and the possibility of multi-layer structures consisting of bcc-hcp composites within the inner core. Our work clarifies nickel's substantial impact on the inner core structure, providing new constraints for the study of core's composition and formation.

physics.geo-ph↗

arXiv2025

Ferroelasticity, shear modulus softening, and the tetragonal-cubic transition in davemaoite

Davemaoite (Dm), the cubic phase of CaSiO3-perovskite (CaPv), is a major component of the Earth's lower mantle. Understanding its elastic behavior, including its dissolution in bridgmanite (MgSiO3-perovskite), is crucial for interpreting lower mantle seismology. Using machine-learning interatomic potentials and molecular dynamics, we investigate CaPv's elastic properties across the tetragonal-cubic transition. Our equations of state align well with experimental data at 300 K and 2,000 K, demonstrating the predictive accuracy of our trained potential. We simulate the ferroelastic hysteresis loop in tetragonal CaPv, which has yet to be investigated experimentally. We also identify a significant temperature-induced shear modulus softening near the phase transition, characteristic of ferroelastic-paraelastic transitions. Unlike previous elasticity studies, our softening region does not extend to slab geotherm conditions. We suggest that ab initio-quality computations provide a robust benchmark for shear elastic softening associated with ferroelasticity, a challenging property to measure in these materials.

cond-mat.mtrl-sci↗

arXiv2025

Spin state of iron in I-42d-type Mg2SiO4 at ultra-high pressures

At extreme pressures of approximately 500 GPa, conditions characteristic of the deep interiors of super-Earths, the combination of NaCl-type MgO and post-perovskite-type MgSiO3 (PPv) has been reported to produce a post-PPv phase of Mg2SiO4 with an I-42d symmetry. This post-PPv (pppv) silicate is proposed as the primary mantle silicate in these massive rocky exoplanets. Understanding the fundamental properties of pppv, particularly in solid solutions with Fe2SiO4, is crucial for insights into the interior dynamics and compositions of such planets. In this study, we conduct an ab initio investigation of the properties of Fe2+-bearing pppv at pressures ranging from 400 GPa to 1 TPa. Given the localized nature of 3d-electrons in iron, we employ the LDA+Usc method alongside conventional DFT functionals to probe the electronic structure of this system. The dependence of the Hubbard parameter U on volume and spin state is carefully evaluated. Furthermore, we systematically explore the effects of pressure, temperature, and structural variations on the spin state of iron in Fe2+-bearing pppv, providing valuable data to improve mantle modeling for super-Earth-type exoplanets.

cond-mat.mtrl-sci↗

arXiv2025

Understanding the two-step nucleation of iron at Earth's inner core conditions: a comparative molecular dynamics study

Metastable phases can lead to multistep nucleation processes, influencing the liquid-to-solid transition in various systems. In this study, we investigate the homogeneous nucleation of iron's crystalline phases under Earth's inner core conditions, employing two previously developed interatomic potentials. We compare the thermodynamic and kinetic properties of iron relevant to the nucleation as predicted by these potentials. While the potentials differ in their predictions of melting temperature by a few hundred Kelvin, they show a consistent description of the relative Gibbs free energy between solid and liquid phases with respect to the undercooling. Both potentials also predict that the metastable bcc phase exhibits a significantly higher nucleation rate than the hcp phase over a wide range of undercooling temperatures below the melting point. This substantially lowers the undercooling thresholds required for the initial nucleation of Earth's inner core. The results validate the commonality of the two-step nucleation mechanism of iron under Earth's inner core conditions for two different potentials, providing a foundation for future studies about the influence of other elements on the nucleation of Earth's core.

physics.geo-ph↗

arXiv2024

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

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.

physics.geo-ph↗

arXiv2024

Probing the state of hydrogen in $δ$-AlOOH at mantle conditions with machine learning potential

Hydrous and nominally anhydrous minerals (NAMs) are a fundamental class of solids of enormous significance to geophysics. They are the water carriers in the deep geological water cycle and impact structural, elastic, plastic, and thermodynamic properties and phase relations in Earth's forming aggregates (rocks). They play a critical role in the geochemical and geophysical processes that shape the planet. Their complexity has prevented predictive calculations of their properties, but progress in materials simulations ushered by machine learning potentials is transforming this state of affairs. Here, we adopt a hybrid approach that combines deep learning potentials (DP) with the SCAN meta-GGA functional to simulate a prototypical hydrous system. We illustrate the success of this approach to simulate $δ$-AlOOH ($δ$), a phase capable of transporting water down to near the core-mantle boundary of the Earth (~2,900 km depth and ~135 GPa) in subducting slabs. A high-throughput sampling of phase space using molecular dynamics simulations with DP-potentials sheds light on the hydrogen-bond behavior and proton diffusion at geophysical conditions. These simulations provide a pathway for a deeper understanding of these crucial components that shape Earth's internal state.

physics.comp-ph↗

arXiv2024

Deep-learning-based prediction of the tetragonal$\rightarrow$cubic transition in davemaoite

Davemaoite, i.e., $CaSiO_3$ perovskite (CaPv), is the third most abundant phase in the lower mantle and exhibits a tetragonal-cubic phase transition at high pressures and temperatures. The phase boundary in CaPv has recently been proposed to be close to the cold slab adiabatic and cause mid-mantle seismic wave speed anomalies (Thomson et al., Nature 572, 643, 2019). In this study, we utilized accurate deep-learning-based simulations and thermodynamic integration techniques to compute free energies at temperatures ranging from 300 to 3,000 K and pressures up to 130 GPa. Our results indicate that CaPv exhibits a single cubic phase throughout lower-mantle conditions. This suggests that the phase diagram proposed by Thomson et al. requires revision, and mid-mantle seismic anomalies are likely attributable to other mechanisms.

physics.geo-ph↗

arXiv2023

Ab initio study on the stability and elasticity of brucite

Brucite (Mg(OH)$_2$) is a mineral of great interest owing to its various applications and roles in geological processes. Its structure, behavior under different conditions, and unique properties have been the subject of numerous studies and persistent debate. As a stable hydrous phase in subduction zones, its elastic anisotropy can significantly contribute to the seismological properties of these regions. We performed ab initio calculations to investigate brucite's stability, elasticity, and acoustic velocities. We tested several exchange-correlation functionals and managed to obtain stable phonons for the P$\bar{3}$ phase with r$^2$SCAN for the first time at all relevant pressures up to the mantle transition zone. We show that r$^2$SCAN performs very well in brucite, reproducing the experimental equation of state and several key structure parameters related to hydrogen positions. The room temperature elasticity results in P$\bar{3}$ reproduces the experimental results at ambient pressure. These results, together with the stable phonon dispersion of P$\bar{3}$ at all relevant pressures, indicate P$\bar{3}$ is the stable candidate phase not only at elevated pressures but also at ambient conditions. The success of r$^2$SCAN in brucite, suggests this functional should be suitable for other challenging layer-structured minerals, e.g., serpentines, of great geophysical significance.

cond-mat.mtrl-sci↗

arXiv2023

Unveiling the effect of Ni on the formation and structure of Earth's inner core

Ni is the second most abundant element in the Earth's core. Yet, its effects on the inner core's structure and formation process are usually disregarded because of its electronic and size similarity with Fe. Using ab initio molecular dynamics simulations, we find that the bcc phase can spontaneously crystallize in liquid Ni at temperatures above Fe's melting point at inner core pressures. The melting temperature of Ni is shown to be 700-800 K higher than that of Fe at 323-360 GPa. hcp, bcc, and liquid phase relation differ for Fe and Ni. Ni can be a bcc stabilizer for Fe at high temperatures and inner core pressures. A small amount of Ni can accelerate Fe's crystallization at core pressures. These results suggest Ni may substantially impact the structure and formation process of the solid inner core.

cond-mat.mtrl-sci↗

arXiv2023

Thermoelastic properties of bridgmanite using Deep Potential Molecular Dynamics

MgSiO_3-perovskite (MgPv) plays a crucial role in the Earth's lower mantle. This study combines deep-learning potential (DP) with density functional theory (DFT) to investigate the structural and elastic properties of MgPv under lower mantle conditions. To simulate complex systems, we developed a series of potentials capable of faithfully reproducing DFT calculations using different functionals, such as LDA, PBE, PBEsol, and SCAN meta-GGA functionals. The obtained predictions exhibit remarkable reliability and consistency, closely resembling experimental measurements. Our results highlight the superior performance of the DP-SCAN and DP-LDA in accurately predicting high-temperature equations of states and elastic properties. This hybrid computational approach offers a solution to the accuracy-efficiency dilemma in obtaining precise elastic properties at high pressure and temperature conditions for minerals like MgPv, which opens a new way to study the Earth's interior state and related processes.

physics.geo-ph↗