arXiv subjects

Luc Belloni

Publications and source records attributed to Luc Belloni.

11 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

A Molecular Density Functional Theory of aqueous electrolytic solution

We propose a generalisation of molecular density functional theory to describe inhomogeneous solvent mixture, with the objective of modelling electrolytic solutions. Two electrolytic models are presented, both within the HNC approximation. The first one is a two-components mixture representing a primitive-like model of sodium chloride, where the solvent is described as a dielectric continuum. This popular model has the advantage of simplicity, as the ions densities solely depend on spatial coordinates. Additionally, we develop a realistic three-components electrolyte model, in which water solvent is described by a third density field that depends on both spatial and orientational coordinates. The proposed methodology and its tridimensional implementation (3 spatial coordinates and 3 Euler angles) are validated by comparing the solvation properties of a sodium cation with the predictions of integral equation theory solved in 1D (1 intermolecular distance and 5 Euler angles), showing near-perfect agreement. This methodology enables the study of solvation properties of solutes of arbitrary shapes in electrolytic solutions, as demonstrated with the prototypical N-methylacetamide molecule immersed in both electrolytic solution models.

physics.chem-ph↗

arXiv2024

The orientational structure of a model patchy particle fluid: simulations, integral equations, density functional theory and machine learning

We investigate the orientational properties of a homogeneous and inhomogeneous tetrahedral 4-patch fluid (Kern--Frenkel model). Using integral equations, either (i) HNC or (ii) a modified HNC scheme with simulation input, the full orientational dependence of pair and direct correlation functions is determined. Density functionals for the inhomogeneous problem are constructed via two different methods. The first, molecular density functional theory, utilizes the full direct correlation function and an isotropic hard-sphere bridge functional. The second method, a machine learning approach, uses a decomposition of the functional into an isotropic reference part and a mean-field orientational part, where both parts are improved by machine learning techniques. Comparison to simulation data at hard walls and around hard tracers show a similar performance of the two functionals. Machine learning strategies are discussed to eliminate residual differences, with the goal of obtaining machine-learning enhanced functionals for the general anisotropic fluid.

cond-mat.soft↗

arXiv2023

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↗

arXiv2023

Grand-canonical molecular dynamics simulations powered by a hybrid 4D nonequilibrium MD/MC method: Implementation in LAMMPS and applications to electrolyte solutions

Molecular simulations in an open environment, involving ion exchange, are necessary to study various systems, from biosystems to confined electrolytes. However, grand-canonical simulations are often computationally demanding in condensed phases. A promising method (L. Belloni, J. Chem. Phys., 2019), one of the hybrid nonequilibrium molecular dynamics/Monte Carlo algorithms, was recently developed, which enables efficient computation of fluctuating number or charge density in dense fluids or ionic solutions. This method facilitates the exchange through an auxiliary dimension, orthogonal to all physical dimensions, by reducing initial steric and electrostatic clashes in three-dimensional systems. Here, we report the implementation of the method in LAMMPS with a Python interface, allowing facile access to grand-canonical molecular dynamics (GCMD) simulations with massively parallelized computation. We validate our implementation with two electrolytes, including a model Lennard-Jones electrolyte similar to a restricted primitive model and aqueous solutions. We find that electrostatic interactions play a crucial role in the overall efficiency due to their long-range nature, particularly for water or ion-pair exchange in aqueous solutions. With properly screened electrostatic interactions and bias-based methods, our approach enhances the efficiency of salt-pair exchange in Lennard-Jones electrolytes by approximately four orders of magnitude, compared to conventional grand-canonical Monte Carlo. Furthermore, the acceptance rate of NaCl-pair exchange in aqueous solutions at moderate concentrations reaches about 3 $\%$ at the maximum efficiency.

physics.chem-ph↗

arXiv2023

Dielectric response of confined water films: Insights from classical DFT

We re-examine the problem of the dielectric response of highly polar liquids such as water in confinement between two walls using a simple two-variable density functional theory involving number and polarisation densities. In the longitudinal polarisation case where a perturbing field is applied perpendicularly to the walls, we show that the notion of local dielectric constant, although ill-defined at a microscopic level, makes sense when a coarse-graining over the typical size of a particle is introduced. The approach makes it possible to study the effective dielectric response of thin liquid films of various thicknesses in connection to the recent experiments of [Fumagalli et al. , Science, 2018, 360, 1339-1342], and to discuss the notion interfacial dielectric constant. We argue that the observed properties as function of slab dimension, in particular the very low dielectric constants of the order of 2-3 measured for thin slabs of 1 nm thickness do not highlight any special property of water but can be recovered for a generic polar solvent having similar particle size and the same high dielectric constant. Regarding the transverse polarisation case where the perturbing field is parallel to the walls, the associated effective dielectric constant as a function of the slab dimension reaches bulk-like values at much shorter widths than in the longitudinal case.

cond-mat.stat-mech↗

arXiv2020

Predicting hydration free energies of the FreeSolv database of druglike molecules with molecular density functional theory

We assess the performance of molecular densityfunctional theory (MDFT) to predict hydration freeenergies of the small drug-like molecules benchmark,FreeSolv. MDFT in the hyper-netted chain approx-imation (HNC) coupled with a pressure correctionpredicts experimental hydration free energies of theFreeSolv database within 1 kcal/mol with an averagecomputation time of two cpu.min per molecule. Thisis the same accuracy as for simulation based free en-ergy calculations that typically require hundreds ofcpu.h or tens of gpu.h per molecule.

physics.chem-ph↗

arXiv2018

High-throughput free energies and water maps for drug discovery by molecular density functional theory

The hydration or binding free energy of a drug-like molecule is a key data for early stage drug discovery. Hundreds of thousands of evaluations are needed, which rules out the exhaustive use of atomistic simulations and free energy methods. Instead, the current docking and screening processes are today relying on numerically efficient scoring functions that lose much of the atomic scale information and hence remain error-prone. In this article, we show how a probabilistic description of molecular liquids as implemented in the molecular density functional theory predicts hydration free energies of a state-of-the-art benchmark of small drug-like molecules within 0.5 kJ/mol (0.1 kcal/mol) of atomistic simulations, along with water and polarization maps, for a computation time compatible with screening and docking.

physics.chem-ph↗

arXiv2018

Screened Coulombic Orientational Correlations in Dilute Aqueous Electrolytes

The ion-induced long-range orientational order between water molecules recently observed in second harmonic scattering experiments and illustrated with large scale molecular dynamics simulations is quantitatively explained using the Ornstein-Zernike integral equation approach of liquid physics. This general effect, not specific to hydrogen-bonding solvents, is controlled by electroneutrality condition, dipolar interactions and dielectric+ionic screening. As expected, all numerical theories recover the well-known analytical expressions established 40 years ago.

physics.chem-ph↗

arXiv2017

Bridge functional for the molecular density functional theory with consistent pressure and surface tension and its importance for solvation in water

We address the problem of predicting the solvation free energy and equilibrium solvent density profile in fews minutes from the molecular density functional theory beyond the usual hypernetted-chain approximation. We introduce a bridge functional of a coarse-grained, weighted solvent density. In few minutes at most, for solutes of sizes ranging from small compounds to large proteins, we produce (i) an estimation of the free energy of solvation within 1 kcal/mol of the experimental data for the hydrophobic solutes presented here, and (ii) the solvent distribution around the solute. Contrary to previous propositions, this bridge functional is thermodynamically consistent in that it produces the correct liquid-vapor coexistence and the experimental surface tension. We show this consistency to be of crucial importance for water at room temperature and pressure. This bridge functional is designed to be simple, local, and thus numerically efficient. Finally, we illustrate this new level of molecular theory of solutions with the study of the hydration shell of a protein.

physics.chem-ph↗

arXiv2017

Efficient molecular density functional theory using generalized spherical harmonics expansions

We show that generalized spherical harmonics are well suited for representing the space and orientation molecular density in the resolution of the molecular density functional theory. We consider the common system made of a rigid solute of arbitrary complexity immersed in a molecular solvent, both represented by molecules with interacting atomic sites and classical force fields. The molecular solvent density $\rho(\mathbf{r},\mathbf{\Omega})$ around the solute is a function of the position $\mathbf{r}\equiv(x,y,z)$ and of the three Euler angles $\mathbf{\Omega}\equiv(\theta,\phi,\psi)$ describing the solvent orientation. The standard density functional, equivalent to the HNC closure for the solute-solvent correlations in the liquid theory, is minimized with respect to $\rho(\mathbf{r},\mathbf{\Omega})$. The up-to-now very expensive angular convolution products are advantageously replaced by simple products between projections onto generalized spherical harmonics. The dramatic gain in speed of resolution enables to explore in a systematic way molecular solutes of up to nanometric sizes in arbitrary solvents and to calculate their solvation free energy and associated microscopic solvent structure in at most a few minutes. We finally illustrate the formalism by tackling the solvation of molecules of various complexity in water.

physics.chem-ph↗