Peter Mausbach

Solid-liquid phase equilibria of the Gaussian core model fluid

The solid-liquid phase equilibria of the Gaussian core model are determined using the GWTS [J. Ge, G.-W. Wu, B. D. Todd, and R. J. Sadus, J. Chem. Phys. 119, 11017 (2003)] algorithm, which combines equilibrium and nonequilibrium molecular dynamics simulations. This is the first reported use of the GWTS algorithm for a fluid system displaying a reentrant melting scenario. Using the GWTS algorithm, the phase envelope of the Gaussian core model can be calculated more precisely than previously possible. The results for the low-density and the high-density (reentrant melting) sides of the solid state are in good agreement with those obtained by Monte Carlo simulations in conjunction with calculations of the solid free energies. The common point on the Gaussian core envelope, where equal-density solid and liquid phases are in coexistence, could be determined with high precision.

Thermodynamic properties in the molecular dynamics ensemble applied to the Gaussian core model fluid

The thermodynamic properties of pressure, energy, isothermal pressure coefficient, thermal expansion coefficient, isothermal and adiabatic compressibilities, isobaric and isochoric heat capacities, Joule-Thomson coefficient, and speed of sound are considered in a classical molecular dynamics ensemble. These properties were obtained using the treatment of Lustig [J. Chem. Phys. 100, 3048 (1994)] and Meier and Kabelac [J. Chem. Phys. 124, 064104 (2006)], whereby thermodynamic state variables are expressible in terms of phase-space functions determined directly from molecular dynamics simulations. The complete thermodynamic information about an equilibrium system can be obtained from this general formalism. We apply this method to the gaussian core model fluid because the complex phase behavior of this simple model provides a severe test for this treatment. Waterlike and other anomalies are observed for some of the thermodynamic properties of the gaussian core model fluid.

Transport Anomalies in the Gaussian Core Model Fluid

Abstract In this study, we investigate the self-diffusion coefficient, the shear viscosity and the thermal conductivity of a single-component system interacting via a Gaussian core (GC) potential. The transport properties are studied by means of the Green-Kubo formulas calculated from molecular dynamics simulation. We show that, for certain state conditions, anomalous behaviour occurs for the diffusivity and the shear viscosity. Therefore, the Stokes-Einstein relation is violated for the GC fluid. We do not find anomalous behaviour for the thermal conductivity. We develop an equation of state for the deviation of the ideal gas pressure and we derive the excess entropy from this equation. Depending on the phase space region, the excess entropy also shows anomalous behaviour. We discuss recently developed scaling relationships between excess entropy and transport properties. Because the GC potential is bounded, these relationships do not work properly for the GC fluid. Using new empirical scaling relations we are able to fit the diffusion coefficient within one single master curve for the whole density and temperature range we have simulated. We were also able to find a single master curve for the viscosity, but only for state conditions where the classical Stokes-Einstein relation is valid.