arXiv subjects

Antoine Carof

Publications and source records attributed to Antoine Carof.

6 recordsLinked to original sources

arXiv2026

Accurate Solvation Properties in supercritical CO$_2$ with Molecular Density Functional Theory

Supercritical CO$_2$ is a highly efficient solvent for the development of more environmentally benign chemical processes. It is crucial to predict its solvation properties -- the solvation free energy and the solvation structure -- both accurately and at low computational cost. We show here that classical density functional theory (cDFT) can reproduce the solvation properties obtained from conventional molecular simulations, while requiring a computational effort that is several orders of magnitude lower. This excellent agreement is achieved using a molecular cDFT formalism based on a density that depends on both the positions and orientations of CO$_2$ molecules in the vicinity of the solute. We further examine several levels of approximation for the excess free-energy functional in cDFT and demonstrate that the homogeneous reference fluid approximation is sufficient to recover the molecular dynamics (MD) benchmark results. These findings open the way to extending molecular cDFT to other thermodynamic conditions.

physics.chem-ph↗

arXiv2025

Non-Gaussian density fluctuations in the Dean-Kawasaki equation

Computing analytically the $n$-point density correlations in systems of interacting particles is a long-standing problem of statistical physics, with a broad range of applications, from the interpretation of scattering experiments in simple liquids, to the understanding of their collective dynamics. For Brownian particles, i.e. with overdamped Langevin dynamics, the microscopic density obeys a stochastic evolution equation, known as the Dean-Kawasaki equation. In spite of the importance of this equation, its complexity makes it very difficult to analyze the statistics of the microscopic density beyond simple Gaussian approximations. In this work, resorting to a path-integral description of the stochastic dynamics and relying on a saddle-point analysis in the limit of high density and weak interactions between the particles, we go beyond the usual linearization of the Dean-Kawasaki equation, and we compute exactly the three- and four-point density correlation functions. This result opens the way to using the Dean-Kawasaki equation beyond the simple Gaussian treatments, and could find applications to understand many fluctuation-related effects in soft and active matter systems.

cond-mat.stat-mech↗

arXiv2024

Stochastic density functional theory for ions in a polar solvent

In recent years, the theoretical description of electrical noise and fluctuation-induced effects in electrolytes has gained a renewed interest, enabled by stochastic field theories like stochastic density functional theory (SDFT). Such models, however, treat solvents implicitly, ignoring their generally polar nature. In the present study, starting from microscopic principles, we derive a fully explicit SDFT theory that applies to ions in a polar solvent. These equations are solved to compute observables like dynamic charge structure factors and dielectric susceptibilities. We unveil the relative importance of the different contributions (solvent, ions, cross terms) to the dynamics of electrolytes, which are key to understand the couplings between ions and the fluctuations of their microscopic environment.

cond-mat.soft↗

arXiv2024

Molecular integral equations theory in the near critical region of CO2

Environmental concerns are driving the search for greener yet efficient solvents. Supercritical CO2 (scCO2) is a promising candidate due to its non-toxicity and the potential for reusing CO2 emissions. It also offers a versatile range of properties that can be finely tuned by pressure adjustments. This adaptability is exploited in chemical industry processes such as separation or extraction. The development of new green processes using scCO2 requires an efficient tool for predicting the solvation properties under different conditions. Existing parametric equations for solubility prediction depend on known experimental data, while molecular dynamics (MD) simulations remain expensive for studying different conditions. Both methods are unsuitable for advancing new technologies. The molecular density functional theory (MDFT) offers a promising alternative, combining an accurate microscopic modeling with fast calculations. MDFT necessitates the bulk direct correlation functions, which can be calculated from expensive MD simulations or from approximate yet rapid molecular integral equations. The development of MDFT as a powerful tool to study the solvation in scCO2 will require the construction of an accurate molecular integral equations for scCO2.This paper presents the exact direct correlation functions of scCO2 obtained from MD and compares them with the results of the simplest molecular integral equations, the hypernetted chain approximation (HNC). If HNC fails to provide correct long-range correlations and thermodynamics, it succeeds in reproducing the short-range structure. By using the direct correlation functions obtained from MD and HNC, we demonstrate the efficacy of MDFT in calculating the chemical potential of CO2 in scCO2. The results open the door to the application of MDFT to a wider range of solutes dissolved in scCO2 with different thermodynamic conditions.

physics.chem-ph↗

arXiv2021

NMR relaxation rates of quadrupolar aqueous ions from classical molecular dynamics using force-field specific Sternheimer factors

The nuclear magnetic resonance (NMR) relaxation of quadrupolar nuclei is governed by the electric field gradient (EFG) fluctuations at their position. In classical molecular dynamics (MD), the electron cloud contribution to the EFG can be included via the Sternheimer approximation, in which the full EFG at the nucleus that can be computed using quantum DFT is considered to be proportional to that arising from the external, classical charge distribution. In this work, we systematically assess the quality of the Sternheimer approximation as well as the impact of the classical force field (FF) on the NMR relaxation rates of aqueous quadrupolar ions at infinite dilution. In particular, we compare the rates obtained using an ab initio parametrized polarizable FF, a recently developed empirical FF with scaled ionic charges and a simple empirical non-polarizable FF with formal ionic charges. Surprisingly, all three FFs considered yield good values for the rates of smaller and less polarizable solutes, provided that a model-specific Sternheimer parametrization is employed. Yet, the polarizable and scaled charge FFs yield better estimates for divalent and more polarizable species. We find that a linear relationship between the quantum and classical EFGs holds well in all of the cases considered, however, such an approximation often leads to quite large errors in the resulting EFG variance, which is directly proportional to the computed rate. We attempted to reduce the errors by including first order nonlinear corrections to the EFG, yet no clear improvement for the resulting variance has been found. The latter result indicates that more refined methods for determining the EFG at the ion position, in particular those that take into account the instantaneous atomic environment around an ion, might be necessary to systematically improve the NMR relaxation rate estimates in classical MD.

physics.chem-ph↗

arXiv2016

Molecular hydrodynamics from memory kernels

The memory kernel for a tagged particle in a fluid, computed from molecular dynamics simulations, decays algebraically as $t^{-3/2}$. We show how the hydrodynamic Basset-Boussinesq force naturally emerges from this long-time tail and generalize the concept of hydrodynamic added mass. This mass term is negative in the present case of a molecular solute, at odds with incompressible hydrodynamics predictions. We finally discuss the various contributions to the friction, the associated time scales and the cross-over between the molecular and hydrodynamic regimes upon increasing the solute radius.

physics.comp-ph↗