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Renzo Vallauri

Publications and source records attributed to Renzo Vallauri.

5 recordsLinked to original sources

Development of a new polarizable potential model of hydrogen fluoride and comparison with other effective models in liquid and supercritical states.

Development of a new polarizable potential of hydrogen fluoride through the reparametrization of the JV-P model is presented: The length of the H-F bond has been shortened and the other parameters of the model have been readjusted accordingly. The structural, thermodynamic, and liquid-vapor equilibrium properties of the new model are compared with those of other effective potential models of HF as well as with experimental data in a broad range of thermodynamic states, from near-freezing to supercritical conditions. It is found that although the reparametrization does not change the structural properties of the HF model noticeably at the level of the pair correlations, it improves the reproduction of the thermodynamic properties of hydrogen fluoride over the entire range of existence of a thermodynamically stable liquid phase and also that of the vapor-liquid coexistence curve. However, the new model, which still overestimates the close-contact separation of the HF molecules, underestimates the density of the coexisting liquid phase and overestimates the saturation pressure, probably due to the too steep repulsion of the potential function.

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Diffusion of water in confined geometry: the case of a multilamellar bilayer.

The diffusion of water confined in a stack of GM3 ganglioside bilayers is studied by computer simulation. A theoretical analysis of the behavior of the mean square displacement parallel and perpendicular to the bilayer surface is also provided in terms of diffusion equations in a very long time interval, between 2 ps and 2 ns. Such an analysis has allowed us to identify two different time regimes, to clarify the nature of nonlinear time dependence of the mean square displacement, and to give an interpretation to the origin of the often used time dependent diffusion coefficient. Both the effects of spatial inhomogeneities and boundary conditions are demonstrated to be the key points for the interpretation of all these results within a consistent theoretical framework.

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Liquid-vapor and liquid-liquid phase equilibria of the Brodholt-Sampoli-Vallauri polarizable water model.

Liquid-vapor and liquid-liquid phase equilibria of the polarizable Brodholt-Sampoli-Vallauri water model have been investigated by Gibbs ensemble Monte Carlo computer simulations. The coexisting liquid and vapor densities and energy of vaporization of the model is found to be in a reasonable agreement with experimental data in the entire temperature range of liquid-vapor coexistence. The critical temperature and density of the model are found to be 615 K and 0.278 gcm(3), respectively, close to the experimental values of 647.1 K and 0.322 gcm(3). In the supercooled state two distinct liquid-liquid coexistence regions are observed. The existence of liquid-liquid phase separation of a polarizable water model is demonstrated for the first time.

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Free volume properties of a linear soft polymer: a computer simulation study.

Molecular dynamics simulation of a linear soft polymer has been performed and the free volume properties of the system have been analyzed in detail in terms of the Voronoi polyhedra of the monomers. It is found that there are only small density fluctuations present in the system. The local environment of the monomers is found to be rather spherical, even in comparison with liquids of atoms or small molecules. The monomers are found to be, on average, eight coordinated by their nearest geometric neighbors, including intra-chain and inter-chain ones. The packing of the monomers is found to be rather compact, in a configuration of 1900 monomers there are, on average, only three voids large enough to incorporate a spherical particle as large as a monomer, indicating that the density of the large vacancies in the system is considerably, i.e., by a few orders of magnitude lower than in molecular liquids corresponding to roughly the same reduced densities.

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Temperature of maximum density line of a polarizable water model.

Monte Carlo simulations of liquid water were performed with a polarizable model in a narrow range of temperatures around the temperature of maximum density (TMD) and a broad pressure range, extended also to negative pressures. In order to infer features of the phase diagram relevant for the explanation of the anomalous behavior of water the pressure dependence of the TMD line was analyzed. The TMD is found to increase with decreasing pressure up to 274.8 K at -32 bar, and decrease upon further stretching. This behavior excludes the possibility of a reentrant liquid-gas spinodal line.

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