arXiv subjects

Renata Wentzcovitch

Publications and source records attributed to Renata Wentzcovitch.

8 recordsLinked to original sources

arXiv2026

Lattice dynamics and the spectroscopic signatures of H-bond disorder in $δ$-AlOOH

Raman and infrared anomalies associated with H-bond symmetrization in $δ$-AlOOH, including mode softening and linewidth broadening at 5-10 GPa, occur at significantly lower pressures than predicted by static harmonic theory. To resolve this discrepancy, we combine harmonic phonon calculations with strongly constrained and appropriately normed (SCAN)-based deep-potential molecular dynamics and phonon quasiparticle analysis at 300 K. This framework extracts temperature- and pressure-dependent frequencies and lifetimes from long-time trajectories, capturing the branch reorganization and rapid linewidth growth characteristic of the disordering regime. Incorporating quasiparticle renormalization and directional longitudinal-optical-transverse-optical (LO-TO) splitting further yields near-quantitative agreement with the ambient-pressure OH-stretching Raman multiplet. These results identify finite-temperature dynamical effects and the progressive loss of spectral coherence as the origin of the spectroscopic signatures of H-bond symmetrization.

cond-mat.mtrl-sci↗

arXiv2026

A quiet quantum revolution in Earth's deep interior

The Earth's lower mantle hosts a subtle but pervasive quantum phenomenon: the pressure-induced spin crossover of iron in its dominant minerals, bridgmanite and ferropericlase. In this transition, iron ions gradually shift from high-spin to low-spin electronic states without structural change, altering their volume, compressibility, and elastic properties. Although long recognized experimentally and theoretically, its geophysical significance has only recently become clear through the integration of mineral physics and three-dimensional seismic imaging. The spin crossover reduces bulk modulus and P-wave velocities while leaving S-wave speeds largely unaffected, producing a distinctive decoupling between P- and S-wave anomalies. This signature is now observed in global tomography and reconciles seismic observations with realistic mantle temperatures and compositions. Rather than forming a sharp boundary, the crossover extends across most of the lower mantle, acting as a diffuse yet essential control on seismic structure. This work highlights how quantum-scale electronic transitions influence planetary-scale dynamics and interpretations of Earth's deep interior.

physics.geo-ph↗

arXiv2024

Machine learning potential for serpentines

Serpentines are layered hydrous magnesium silicates (MgO$\cdot$SiO$_2\cdot$H$_2$O) formed through serpentinization, a geochemical process that significantly alters the physical property of the mantle. They are hard to investigate experimentally and computationally due to the complexity of natural serpentine samples and the large number of atoms in the unit cell. We developed a machine learning (ML) potential for serpentine minerals based on density functional theory (DFT) calculation with the r$^2$SCAN meta-GGA functional for molecular dynamics simulation. We illustrate the success of this ML potential model in reproducing the high-temperature equation of states of several hydrous phases under the Earth's subduction zone conditions, including brucite, lizardite, and antigorite. In addition, we investigate the polymorphism of antigorite with periodicity $m$ = 13--24, which is believed to be all the naturally existent antigorite species. We found that antigorite with $m$ larger than 21 appears more stable than lizardite at low temperatures. This machine learning potential can be further applied to investigate more complex antigorite superstructures with multiple coexisting periodic waves.

physics.geo-ph↗

arXiv2024

Elasticity and acoustic velocities of $δ$-AlOOH at extreme conditions: a methodology assessment

Hydrous phases play a fundamental role in the deep-water cycle on Earth. Understanding their stability and thermoelastic properties is essential for constraining their abundance using seismic tomography. However, determining their elastic properties at extreme conditions is notoriously challenging. The challenges stem from the complex behavior of hydrogen bonds under high pressures and temperatures (P,Ts). In this study, we evaluate how advanced molecular dynamics simulation techniques can address these challenges by investigating the adiabatic elasticity and acoustic velocities of $δ$-AlOOH, a critical and prototypical high-pressure hydrous phase. We compared the performances of three methods to assess their viability and accuracy. The thermoelastic tensor was computed up to 140 GPa and temperatures up to 2,700 K using molecular dynamics with a DeePMD machine-learning interatomic potential based on the SCAN meta-GGA functional. The excellent agreement with ambient condition single-crystal ultrasound measurements and the correct description of velocity changes induced by H-bond disorder-symmetrization transition observed at 10 GPa in Brillouin scattering measurements underscores the accuracy and efficacy of our approach.

physics.comp-ph↗

arXiv2024

Fe2+ partitioning in Al-free pyrolite: consequences for seismic velocities and heterogeneities

Iron partitioning among the main lower mantle phases, bridgmanite (Bm) and ferropericlase (Fp), has non-monotonic behavior owing to the high-spin to low-spin crossover in ferrous iron (Fe2+) in Fp. Results of previous studies of the iron partitioning coefficient between these phases, $K_D$, still have considerable uncertainty. Here, we investigate the Fe2+ partitioning behavior using well-documented ab initio free energy results plus new updates. Although we focus on Fe2+ only, we describe the effect of this iron spin crossover (ISC) on $K_D$ and of the latter on compositions and seismic velocities in a pyrolitic aggregate. Our results suggest that its velocities are mainly affected by the ISC and less so by the Fe2+ partitioning. In contrast, iron partitioning manifests in thermally induced velocity heterogeneity ratios. Prediction of the seismological parameter $R_{S/P}$ ($\partial \ln V_S/\partial \ln V_P$) including iron partitioning effects resembles quantitatively $R_{S/P}$'s inferred from several tomographic studies down to 2,400 km depth.

cond-mat.mtrl-sci↗

arXiv2023

DeePMD-kit v2: A software package for Deep Potential models

DeePMD-kit is a powerful open-source software package that facilitates molecular dynamics simulations using machine learning potentials (MLP) known as Deep Potential (DP) models. This package, which was released in 2017, has been widely used in the fields of physics, chemistry, biology, and material science for studying atomistic systems. The current version of DeePMD-kit offers numerous advanced features such as DeepPot-SE, attention-based and hybrid descriptors, the ability to fit tensile properties, type embedding, model deviation, Deep Potential - Range Correction (DPRc), Deep Potential Long Range (DPLR), GPU support for customized operators, model compression, non-von Neumann molecular dynamics (NVNMD), and improved usability, including documentation, compiled binary packages, graphical user interfaces (GUI), and application programming interfaces (API). This article presents an overview of the current major version of the DeePMD-kit package, highlighting its features and technical details. Additionally, the article benchmarks the accuracy and efficiency of different models and discusses ongoing developments.

physics.chem-ph↗

arXiv2023

Full-waveform tomography reveals iron spin crossover in Earth lower mantle

Joint interpretation of bulk and shear wave speeds constrains the chemistry of the deep mantle. At all depths, the diversity of wave speeds cannot be explained by an isochemical mantle. Between 1000 and 2500 km depth, hypothetical mantle models containing an electronic spin crossover in (Mg,Fe)O provide a significantly better fit to the wave-speed distributions, as well as more realistic temperatures and silica contents, than models without a spin crossover. Below 2500 km, wave speed distributions are explained by enrichment in silica towards the core-mantle-boundary. This silica enrichment may represent the fractionated remains of an ancient basal magma ocean.

physics.geo-ph↗

arXiv2019

phq: a Fortran code to compute phonon quasiparticle properties and dispersions

We here introduce a Fortran code that computes anharmonic free energy of solids from first-principles based on our phonon quasiparticle approach. In this code, phonon quasiparticle properties, i.e., renormalized phonon frequencies and lifetimes, are extracted from mode-projected velocity auto-correlation functions (VAF) of modes sampled by molecular dynamics (MD) trajectories. Using renormalized frequencies as input, the code next constructs an effective harmonic force constant matrix to calculate anharmonic phonon dispersions over the whole Brillouin zone and thus the anharmonic free energy in the thermodynamic limit ($N \rightarrow \infty$). We illustrate the use of this code to compute ab initio temperature-dependent anharmonic phonons of Si in the diamond structure.

cond-mat.mtrl-sci↗