Optimized intermolecular potential for nitriles based on Anisotropic United Atoms model

An extension of the Anisotropic United Atoms intermolecular potential model is proposed for nitriles. The electrostatic part of the intermolecular potential is calculated using atomic charges obtained by a simple Mulliken population analysis. The repulsion-dispersion interaction parameters for methyl and methylene groups are taken from transferable AUA4 literature parameters [Ungerer et al., J. Chem. Phys., 2000, 112, 5499]. Non-bonding Lennard-Jones intermolecular potential parameters are regressed for the carbon and nitrogen atoms of the nitrile group (–C≡N) from experimental vapor-liquid equilibrium data of acetonitrile. Gibbs Ensemble Monte Carlo simulations and experimental data agreement is very good for acetonitrile, and better than previous molecular potential proposed by Hloucha et al. [J. Chem. Phys., 2000, 113, 5401]. The transferability of the resulting potential is then successfully tested, without any further readjustment, to predict vapor-liquid phase equilibrium of propionitrile and n-butyronitrile

Equilibrium and transport properties of CO2+N2O and CO2+NO mixtures : a molecular simulation and equation of state modelling study.

International audienceIn the present study, the thermodynamic behaviour and transport properties of CO2+N2O and CO2+NO mixtures have been investigated using molecular simulation and equation of state modelling. Molecular simulations were based on Monte Carlo and Molecular Dynamics calculations using force fields calibrated from pure component properties and no adjustment of mixture properties was performed. Original force fields were proposed for N2O, NO and N2O2 molecules. Special attention must be paid when studying nitric oxide containing systems because this compound can exist as a mixture of monomers (NO) and dimers (N2O2) under certain pressure and temperature conditions. Liquid-vapour coexistence properties of the reacting NO-N2O2 system were thus first investigated using combined reaction ensemble and Gibbs ensemble Monte Carlo methods. Using the new force fields proposed, phase compositions, phase densities and phase viscosities were determined for CO2+NOx mixtures. Due to the strong similarities between carbon dioxide and nitrous oxide (Tc(CO2) = 304.21 K; Tc(N2O) = 309.57 K; Pc(CO2) = 7.38 MPa; Pc(N2O) = 7.24 MPa), the obtained thermodynamic and transport properties for a CO2+N2O mixture with 10 mol% of N2O are similar to pure CO2 properties in the whole range of studied temperatures (273 - 293 K), in agreement with available experimental data. Calculations of CO2+NO equilibrium and transport properties were also performed at three different temperatures in the range of 253 - 273 K. At these temperatures, only the monomer form of the nitric oxide (NO) has to be accounted for. The performed calculations are pure predictions since no experimental data are available in the open literature for this system. For a mixture containing 10 mol% of NO, the simulation results show a decrease of the liquid densities and viscosities of 9% and 24% with respect to corresponding pure CO2 values, respectively. The new pseudo-experimental data generated in this work were finally used to calibrate binary interaction parameters required in standard cubic equations of states. Both Peng-Robinson and Soave-Redlich-Kwong equations of state have been considered and after the regression, they display a decent match with experimental and pseudo-experimental data of the vapour-liquid equilibrium for the two studied mixtures

Calculation of the surface tension of pure tin from atomistic simulations of liquid-vapour systems.

International audienceMonte Carlo simulations of heterogeneous systems of tin at liquid–vapour equilibrium have been performed at several temperatures from 600 to 1500 K, using a modified embedded atom model potential. Surface tension of the corresponding planar interfaces has been evaluated using the test area method. Calculation results are in good agreement with experiments presenting a maximum deviation of 10% from experiments. In addition, the Monte Carlo simulations provide a temperature coefficient (the derivative of the surface tension in regard with temperature) in reasonable agreement with the experimental coefficient

Atomic scale investigation of the diffusion of defects and fission gases in uranium dioxide

International audienceFuel behaviour under irradiation is extremely complex due to the combined effect of radiation and temperature. Actinide fission produces large quantities of defects and fission products, which have a significant influence on the structural, thermal and mechanical properties of nuclear fuels and claddings. A better understanding of atomic transport properties in these materials is central to getting further insight into the irradiation driven micro-structural changes. An efficient approach to unravel the basic mechanisms governing these properties is to couple separate effect experiments and modelling at the atomic scale (1-3). We will present the study of the diffusion of defects and krypton in uranium dioxide (UO2) using atomic scale calculations (4). The migration barriers of the elementary mechanisms are calculated in the DFT+U framework using the nudged elastic band method. The attempt frequencies are obtained from the phonon modes of the defect at the initial and saddle points using empirical potential methods. The preferred mechanisms for defect and Kr migration and the corres-ponding diffusion coefficients as a function of the oxygen chemical potential or nonstoichiometry are then calculated by combining this data with diffusion models adapted to the systems studied

Impact of operational modelling choices on techno-economic modelling of local energy systems

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Slab thickness dependence of the surface tension: Toward a criterion of liquid sheets stability

International audienceMicroscopic Monte Carlo simulations of liquid sheets of copper and tin have been performed in order to study the dependence of the surface tension on the thickness of the sheet. It results that the surface tension is constant with the thickness as long as the sheet remains in one piece. When the sheet is getting thinner, holes start to appear, and the calculated surface tension rapidly decreases with thickness until the sheet becomes totally unstable and forms a cylinder. We assume here that this decrease is not due to a confinement effect as proposed by Werth et al. [Physica A392, 2359 (2013)] on Lennard-Jones systems, but to the appearance of holes that reduces the energy cost of the surface modification. We also show in this work that a link can be established between the stability of the sheet and the local fluctuations of the surface position, which directly depends on the value of the surface tension. Finally, we complete this study by investigating systems interacting through different forms of Lennard-Jones potentials to check if similar conclusions can be drawn

Anisotropic surface stresses of a solid/fluid interface: Molecular dynamics calculations for the copper/methane interface

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A new experimental design for laser-driven shocks on precompressed and preheated water samples

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