arXiv subjects

Laurent Brochard

Publications and source records attributed to Laurent Brochard.

3 recordsLinked to original sources

arXiv2026

A Gaussian process coarse-grained potential for Na-montmorillonite

Hydraulic transport in compacted bentonite is diffusion-controlled and governed by the hydration and microstructure of sodium montmorillonite (Na-MMT). Experiments cannot resolve how platelet interactions govern pore structure, transport and stiffness, while existing coarse-grained models smooth hydration oscillations or require manual corrections. We develop a tabulated potential combining Morse interactions between platelet centre and edge sites with a Gaussian process regression correction trained on all-atom potentials of mean force. It captures the hydration-induced complexity of the potential-of-mean-force profiles, including the three-water (3-W) hydration minimum and transfers across geometries, layer-charge variants and unseen configurations. Applied to monodisperse and polydisperse Na-MMT assemblies at dry densities of 0.8-1.3 g cm^-3, the model captures the 3-W to 1-W transition, loss of non-interlayer porosity and evolution of pore structure, random-walk tortuosity, diffusion and stiffness. Predicted diffusion agrees with compacted Na-bentonite measurements.

cond-mat.mtrl-sci↗

arXiv2024

Investigating the effect of Cu$^{2+}$ sorption in montmorillonite using density functional theory and molecular dynamics simulations

Montmorillonite (MMT) is the main mineral component of bentonite, which is currently proposed as a sealing material in deep geological repositories (DGRs) for used nuclear fuel. In the Canadian program, which will utilize copper-cladded used fuel containers, safety analysis considers the effect of copper corrosion, during which Cu$^{2+}$ ions could potentially be adsorbed by the surrounding MMT. In such a scenario, ion exchange between Na$^+$ and Cu$^{2+}$ is expected. In this study, a multiscale approach that combines electronic density functional theory (DFT) and force-field-based molecular dynamics (MD) simulations was employed to study the effect of introducing Cu$^{2+}$ ions to MMT. An extension to the ClayFF force field is parametrized and validated using DFT to model how Cu$^{2+}$ interacts with clay systems. MD simulations were performed to calculate the interaction free energies between MMT platelets containing Cu$^{2+}$ ions (Cu-MMT) and compared them to inter-platelet interaction energies in Na-MMT and Ca-MMT. Our calculations suggest Cu-MMT develops swelling pressures between those of Ca-MMT and Na-MMT. Furthermore, our MD simulations suggest that Cu$^{2+}$ has MMT interlayer mobility that is significantly slower than that of Ca$^{2+}$.

cond-mat.mtrl-sci↗

arXiv2015

Coupling a reactive potential with a harmonic approximation for atomistic simulations of material failure

Molecular dynamics (MD) simulations involving reactive potentials can be used to model material failure. The empirical potentials which are used in such simulations are able to adapt to the atomic environment, at the expense of a significantly higher computational cost than non-reactive potentials. However, during a simulation of failure, the reactive ability is needed only in some limited parts of the system, where bonds break or form and the atomic environment changes. Therefore, simpler non-reactive potentials can be used in the remainder of the system, provided that such potentials reproduce correctly the behavior of the reactive potentials in this region, and that seamless coupling is ensured at the interface between the reactive and non-reactive regions. In this article, we propose a methodology to combine a reactive potential with a non-reactive approximation thereof, made of a set of harmonic pair and angle interactions and whose parameters are adjusted to predict the same energy, geometry and Hessian in the ground state of the potential. We present a methodology to construct the non-reactive approximation of the reactive potential, and a way to couple these two potentials. We also propose a criterion for on-the-fly substitution of the reactive potential by its non-reactive approximation during a simulation. We illustrate the correctness of this hybrid technique for the case of MD simulation of failure in two-dimensional graphene originally modeled with REBO potential.

cond-mat.mtrl-sci↗