A new approximate bridge function for pure fluids

Approximative "one particle" bridge function B(1)(r) for the theory of simple fluids

New properties for the one particle bridge function B(1)(r), which are necessary to the calculation of the excess chemical potential betamue), are derived for the hard sphere fluid. The method, which only requires the knowledge of the bridge function B(2)(r), is based on an investigation of the correlation function dependence on the Kirkwood charging parameter. In this framework, the unavoidable question of topological homotopy is addressed. As far as B(2)(r) is considered as exact, this work provides useful information on B(1)(r) in the well identified dynamical regimes of the hard sphere fluid. Signatures of the transitions between these regimes are identified on the trends of B(1)(r). This approach provides self-consistent results for betamue) that agree very well with simulation data.

Thermodynamic and dynamic anomalies for a three-dimensional isotropic core-softened potential

Using molecular-dynamics simulations and integral equations (Rogers-Young, Percus-Yevick, and hypernetted chain closures) we investigate the thermodynamics of particles interacting with continuous core-softened intermolecular potential. Dynamic properties are also analyzed by the simulations. We show that, for a chosen shape of the potential, the density, at constant pressure, has a maximum for a certain temperature. The line of temperatures of maximum density (TMD) was determined in the pressure-temperature phase diagram. Similarly the diffusion constant at a constant temperature, D, has a maximum at a density rho(max) and a minimum at a density rho(min) < rho(max). In the pressure-temperature phase diagram the line of extrema in diffusivity is outside of the TMD line. Although this interparticle potential lacks directionality, this is the same behavior observed in simple point charge/extended water.

Structure of inhomogeneous Lennard-Jones fluid near the critical region and close to the vapor-liquid coexistence curve: Monte Carlo and density-functional theory studies

Results for the density profiles of the Lennard-Jones (LJ) fluid subjected to diverse external fields are presented for the Monte Carlo simulations within the grand canonical ensemble and for the third order and second order perturbation density-functional approximation (DFA). In all cases, the bulk LJ fluid in the particle reservoir to which the nonuniform fluid under consideration is connected, is at the conditions situated at "dangerous" regions of the phase diagram, i.e., near the critical temperature or close to the gas-liquid coexistence curve. It is found that the previously investigated third order and second order perturbation DFA for hard core attractive Yukawa fluid [J. Chem. Phys. 122, 064503 (2005)] can perform successfully also for the nonuniform LJ fluid only on the condition of high accuracy of the required bulk second order direct correlation function. The present report further indicates that the proposed third order and second order perturbation DFA is efficient and suitable for both supercritical and subcritical temperatures.

Excess entropy scaling for the diffusion coefficient in expanded liquid metals

Molecular-dynamics simulation is used to compute the pair correlation function and the velocity autocorrelation function of Cs and Rb along the liquid-vapor coexistence curve, from which the excess entropy S(ex) and the diffusion coefficient D are deduced. The numerical results of both physical properties are correlated and a scaling law between the excess entropy and the reduced diffusion coefficient D(*)(=D/D(0)) is investigated for different expressions of the reduction parameter D(0). The choice of thermodynamic states along the liquid--vapor coexistence curve gives us the possibility to extend the investigation of the relation between the reduced diffusion coefficient and the excess entropy over a wide area and to test the adequacy of the scaling law confidently.