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Biomedical subjects

András Baranyai

Publications and source records attributed to András Baranyai.

3 recordsLinked to original sources

Limitations of the rigid planar nonpolarizable models of water.

We analyzed the ability of variants of the SPC/E and TIP4P types of water models to describe the temperature dependence of their second virial coefficients, liquid-vapor phase envelopes, and corresponding coexistence vapor pressure. We complete the characterization of the two most promising models by testing their adequacy to predict the structure of the 13 known crystalline phases of ice by (Parrinello-Rahman) isothermal-isobaric Monte Carlo simulations. While these models perform well for the description of properties to which their force fields were fitted (density, heat of vaporization, structure at the level of pair correlations), their transferability to the entire phase diagram is unsatisfactory, i.e., none could significantly mitigate the shortcomings of the original models. In fact, the most appropriate alternative appears to be the TIP4P-EW model, i.e., the recent reparametrization of the original TIP4P water model. Model parametrizations aimed at improving the description of ice behavior fail even in the description of the liquid phase.

Journal Article↗

Computer simulation of the 13 crystalline phases of ice.

As a reference for follow-up studies toward more accurate model parametrizations, we performed molecular-dynamics and Monte Carlo simulations for all known crystalline phases of ice, as described by the simple point-charge/extended and TIP4P water models. We started from the measured structures, densities, and temperatures, and carried out classical canonical simulations for all these arrangements. All simulated samples were cooled down close to 0 K to facilitate the comparison with theoretical estimates. We determined configurational internal energies as well as pressures, and monitored how accurately the measured configurations were preserved during the simulations. While these two models predicted very similar thermophysical and structural properties for water at ambient conditions, the predicted features for the corresponding ice polymorphs may differ significantly.

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Direct estimation of the partition function from computer simulation.

We propose an approximate method for directly estimating the partition function of classical, many-body model systems. The accessible part of the phase space is determined from a single simulation. We introduce the method for the hard-sphere fluid and solid. The best performance is found in the dense fluid regime, close to freezing density and in the solid crystal. Defining hard-core effective diameters, the method can be applied to systems with soft-core interactions. We present results of exploratory calculations for the Lennard-Jones liquid.

Journal Article↗