Quantifying the effect of deviatoric stress on phase equilibrium, a multiscale approach in a geodynamic perspective

Institut PPRIME; Chasseneuil-du-Poitou; On-site; EUR 20,000 - 27,000; Full time

Job summary

Institut PPRIME in Poitiers, France, invites applications for a PhD position within the ANR MULTI-STEP project. The work focuses on multiscale, stress-driven thermodynamic equilibrium predictions, combining atomistic simulations with large-scale modeling and micromechanical experiments.

The PhD aims to develop deviatoric-stress dependent phase diagrams for titanium and silica, employing molecular dynamics, ab-initio MD, and Gibbs free energy calculations to overcome classical phase equilibrium

Qualifications

• Experience with atomistic simulations and thermodynamics is essential.
• Familiarity with MD methods and free energy calculations is preferred.
• Strong analytical and numerical skills to model multiscale thermodynamic problems.

Responsibilities

• Conduct atomistic simulations to develop deviatoric stress–dependent phase diagrams.
• Compute Gibbs free energies using thermodynamics integration and umbrella sampling.
• Collaborate across WP1–WP5 within the MULTI-STEP project and contribute to manuscript preparation.

Skills

Molecular dynamics

Atomistic simulations

Thermodynamics

Tools

Ab-Initio Molecular Dynamics

Thermodynamics Integration

Umbrella Sampling

Gibbs free energies

Job description

Quantifying the effect of deviatoric stress on phase equilibrium, a multiscale approach in a geodynamic perspective

08/09/2026 Financement public/privé

Quantifying the effect of deviatoric stress on phase equilibrium, a multiscale approach in a geodynamic perspective

atomistic simulations, phase equilibrium, free energy, Earth’s Sciences

Phase transformations (PT) shape the formation of rocks and determine the mechanical properties of many engineered materials, making them a key area of research in both Earth Science and Metallurgy. When subjected to changes in environmental conditions such as pressure or temperature, rocks and metals undergo PTs to achieve thermodynamic equilibrium. In minerals, investigation of mineral assemblages provides essential insights into their conditions of formation. The mineral phases can indeed be used to trace significant geodynamic processes, such as orogenesis, rifting or subduction. In metallic materials, the development of multiple phases is critical for optimizing performance and is an important ingredient in the design of high performance parts in aeronautics, energy, transport, and plenty of other domains. The theory behind the aforementioned PTs relies on the assumption that the stress has the same effect on phase equilibrium as equivalent hydrostatic pressure, meaning the effects of deviatoric stress are neglected. Such hypothesis, however, have recently triggered discussions in both Earth science and Metallurgy. In fact, there are now several experimental results that show non-trivial relation between mechanical pressure and mineral reactions [1], including the quartz/coesite transformation [2], a PT emblematic of Earth’s Science. Similarly, the α/ω transformation of titanium has been shown to be influenced by the applied stress [3].

The PhD thesis will take place at PPRIME Institute (Poitiers, France) in the context of the international ANR project MULTI-STEP: Multiscale Stress-driven Thermodynamic Equilibrium Predictions, in collaboration with the Centre de Mise en Forme des Matériaux (Mines-ParisTech, Sophia Antipolis, France), the Heidelberg University (Germany) and the Goethe University (Frankfurt, Germany). This project aims at understanding the effect of deviatoric stress on the phase fraction equilibrium of titanium and silica. It proposes to overcome the classical hypotheses for phase equilibrium calculations using a multiscale numerical approach, from atomistic to large-scale thermomechanical modeling, coupled with micromechanical experiments.

The PhD thesis will mostly focus on the WP1 of the MULTI-STEP project lying on atomic scale simulations. The main objective of this WP is to provide deviatoric stress-dependant phase diagram for both titanium and silica. In this aim, atomistic simulations will be used in combination with state of the art approaches for computing Gibbs free energies, such as thermodynamics integration [4] or umbrella sampling [5]. The atomic scale approach will also allow to obtain two main ingredients needed for the homogenization performed in WP5. First, the atomistic simulation will allow to derive equations of state for all phases of interest, which will be used to compute the volumetric part of eigenstrains. Second, the bicrystallography will permits from the atomic structure of the crystals to infer the deviatoric part of the eigenstrains related to the different phase transformations.

Depending on the progress of the subject and the candidate's interests, participation in other WPs of the project may be considered.

References:

[1]: S. Cionoiu and et al. “Impact of interseismic deformation on phase transformations and rock properties in subduction zones”. In: Sci. Rep. 9.1 (2019), p. 19561.

[2]: B. Richter and et al. “Stresses and pressures at the quartz-to-coesite phase transformation in shear deformation

[3]: K. Dang and et al. “The role of deviatoric stress and dislocations on the α to ω phase transformation in Ti”. In: Acta

Mater. 244 (2023), p. 118510.

[4]: P. Y. Chew and A. Reinhardt. “Phase diagrams—Why they matter and how to predict them”. In: J. Chem. Phys. 158.3 (2023).

Techniques/methods in use: Molecular dynamics, Ab-Initio Molecular Dynamics, Thermodynamics Integration, Umbrella Sampling

01/12/2026

ANR project

France

UNIVERSITE DE POITIERS

Knowledges in material physics, thermodynamics, interest on numerical simulations