Anisotropic United Atom Model Including the Electrostatic Interactions of Benzene

Thermodynamic, structural and dynamic properties of selected non-associative neat liquids

Non-associative neat liquids benzene, acetone and carbon tetrachloride have been examined via molecular dynamics simulations. Several models of each neat liquid have been simulated, and selected thermodynamic and structural results are presented. However, the models have been compared mainly in terms of their dynamic quantities. Since models are rarely parametrized with the dynamic properties in mind, the principal goal of this work is to present quantities such as the power spectra, rotational correlation functions and relaxation times, diffusion coefficients and self and distinct parts of the van Hove functions in relation to available experimental data. The general trends of the calculated data provide a benchmark for the behavior of neat simple liquids which will be built upon in the cases of mixtures with associative liquids.

Adsorption and Diffusion of Benzene in Mg-MOF-74 with Open Metal Sites

We performed molecular simulations to investigate the adsorption and diffusion of benzene in metal-organic framework Mg-MOF-74. At 300 K and 20 Pa, the saturated loading of benzene reaches 8.2 mmol/g, almost twice of (12,12) single-walled carbon nanotube with a similar pore size, and 93% of the benzene molecules in Mg-MOF-74 can desorb at 390 K. The energy analysis indicates that the van der Waals contribution still dominates 70-80% of the total fluid-wall interaction energy compared with the Coulombic contribution. We further analyzed the structure of benzene confined in Mg-MOF-74 by the molecular snapshots, pair correlation functions, orientational order parameters, and local density profiles. It is found that low temperature and high pressure make the structure of adsorbed benzene more similar to that of the liquid benzene. Moreover, the benzene molecules in the contact adsorption layer lie flat on the surface of adsorbent, whereas those molecules near the pore center have no particular orientations. Due to the existence of open metal sites, the structures of adsorbed benzene are more compact and ordered than those of bulk liquid benzene. Consequently, the self-diffusion coefficient of saturated benzene in Mg-MOF-74 at 300 K is significantly lower than that of bulk liquid benzene and confined liquid benzene in slit pores and disordered carbons by 4-5 orders of magnitude. We investigated the separation and diffusion of benzene/cyclohexane in the mixture in Mg-MOF-74 and found that the pores almost completely adsorbed benzene, although its self-diffusion coefficient was slightly lower than that of cyclohexane.

Chemoinformatics at IFP Energies Nouvelles: Applications in the Fields of Energy, Transport, and Environment

The objective of the present paper is to summarize chemoinformatics based research, and more precisely, the development of quantitative structure property relationships performed at IFP Energies nouvelles (IFPEN) during the last decade. A special focus is proposed on research activities performed in the "Thermodynamics and Molecular Simulation" department, i. e. the use of multiscale molecular simulation methods in responses to projects. Molecular simulation techniques can be envisaged to supplement dataset when experimental information lacks, thus the review includes a section dedicated to molecular simulation codes, development of intermolecular potentials, and some of their possible applications. Know-how and feedback from our experiences in terms of machine learning application for thermophysical property predictions are included in a section dealing with methodological aspects. The generic character of chemoinformatics is emphasized through applications in the fields of energy, transport, and environment, with illustrations for three IFPEN business units: "Transports", "Energy Resources", and "Processes". More precisely, the review focus on different challenges such as the prediction of properties for alternative fuels, the prediction of fuel compatibility with polymeric materials, the prediction of properties for surfactants usable in chemical enhanced oil recovery, and the prediction of guest-host interactions between gases and nanoporous materials in the frame of carbon dioxide capture or gas separation activities.

Significant curvature effects of partially charged carbon nanotubes on electrolyte behavior investigated using Monte Carlo simulations

Carbon nanotubes and graphene are among the major nanomaterials in nanoscience and technology. Despite having π electrons, these nanocarbon allotropes have been simply considered as neutral in classical calculations. In this study, the effects of partial charges on graphene and curved interfaces on molecular adsorption were investigated using Monte Carlo simulations of N2 and NaCl aqueous solutions on graphene and carbon nanotubes. The simulated N2 adsorption behavior and adsorption potential on partially charged and non-charged graphene coincided with each other. The adsorption potentials suggested that partially charged graphene attracted Na ions and repelled Cl ions. However, those tendencies were not present in NaCl aqueous solutions on graphene. Conversely, in partially charged carbon nanotube models, a preference for Na ions and repulsion of Cl ions in the internal nanospaces were observed in the adsorption potentials using Monte Carlo simulations. Curved interfaces in the internal nanospaces of carbon nanotubes enhanced these properties, suggesting significant electrostatic interactions in a curved π-conjugated system.

Adsorption of probe molecules in pillared interlayered clays: experiment and computer simulation

In this paper we investigate the adsorption of various probe molecules in order to characterize the porous structure of a series of pillared interlayered clays (PILC). To that aim, volumetric and microcalorimetric adsorption experiments were performed on various Zr PILC samples using nitrogen, toluene, and mesitylene as probe molecules. For one of the samples, neutron scattering experiments were also performed using toluene as adsorbate. Various structural models are proposed and tested by means of a comprehensive computer simulation study, using both geometric and percolation analysis in combination with Grand Canonical Monte Carlo simulations in order to model the volumetric and microcalorimetric isotherms. On the basis of this analysis, we propose a series of structural models that aim at accounting for the adsorption experimental behavior, and make possible a microscopic interpretation of the role played by the different interactions and steric effects in the adsorption processes in these rather complex disordered microporous systems.

UNITED ATOM MODEL APPROACH FOR DESCRIBING C60 INTERACTION ENERGY IN MOLECULAR MECHANICS

A unified atom model for describing interaction energy between C60 molecules was obtained by Liu and Wang based on the Smith–Thakkar potential function. In view of the mathematical resemblance between the Liu–Wang and the conventional Lennard-Jones (12-6) function (used in computational chemistry software for describing van der Waals energy), modified versions of the Lennard-Jones function are proposed for quantifying the potential energy between C60 molecules. In this way, the Liu–Wang parameters can be converted into Lennard-Jones parameters for ready execution in commercially available computational chemistry software with minimal hard-coding involved. It was found that the Lennard-Jones function reasonably approximates the Liu–Wang model when the former's indices are increased by a factor of (7/4), without introducing any change to the coefficients. A better agreement was found when m = 4n = 35.4857, which also requires the change in repulsive and attractive indices from 1 and 2 to (1/3) and (4/3), respectively.

Adsorption and structure of benzene on silica surfaces and in nanopores

Grand canonical Monte Carlo simulations are used to study the adsorption of benzene on atomistic silica surfaces and in cylindrical nanopores. The effect of temperature and surface chemistry is addressed by studying the adsorption of benzene at 293 and 323 K on both fully and partially hydroxylated silica surfaces or nanopores. We also consider the adsorption of benzene in a cylindrical nanopore of diameter D=3.6 nm and compare our results with those obtained for planar surfaces. The structure of benzene in the vicinity of the planar surface and confined in the cylindrical nanopore is determined by calculating orientational order parameters and examining positional pair correlation functions. The density profiles of adsorbed benzene reveal the strong layering of the adsorbate, which decays with the distance from the silica surface. At a given temperature and at low pressures, the film adsorbed at the fully hydroxylated silica surface is larger than that for the partially hydroxylated silica surface. This result is due to an increase in the density of silanol groups that induces an increase in the polarity of the silica surface, which becomes more attractive for the adsorbate. Our results also suggest that the benzene molecules prefer an orientation in which their ring is nearly perpendicular to the surface when fully hydroxylated surfaces are considered. When partially hydroxylated surfaces are considered, a second preferential orientation is observed where the benzene ring forms an angle of approximately 50 degrees with the silica surface. In this case, the average orientation of the benzene molecules appears disordered as in the bulk phase. These results suggest that determining the experimental orientation of benzene in the vicinity of a silica surface is a difficult task even when the surface chemistry is known. Capillary condensation in the nanopores involves a transition from a partially filled pore (a thin film adsorbed at the pore surface) to a completely filled pore configuration where the confined liquid coexists at equilibrium with the external gas phase. The disordered orientation of the adsorbed benzene molecules in the case of the partially hydroxylated surface favors the condensation of benzene molecules (the condensation pressure for this substrate is lower than that for the fully hydroxylated surface). Finally, these results are consistent with the structural analysis, showing that (1) benzene tends to relax its liquid structure a little in order to optimize its molecular arrangement near the pore wall and (2) the disordering of the liquid structure induced by the surface becomes stronger as the interaction with the pore wall increases.