Binary-collision contributions to atomic motions in fluids

Many-body correlations versus mode-coupling effects in the dynamics of dense gases

Time dependent contributions due to the triplet and quadruplet correlation functions have been combined with microscopically determined contribution due to the pair correlation function for the transverse stress correlation function. Comparison of the results with simulation data shows that contributions due to two- and three-body static correlation functions are sufficient to understand the viscous dynamics of dense gases. However, close to the triple point, it becomes necessary to include the contribution due to the four-body correlation function. The contribution due to the mode coupling effect has been contrasted with the contribution due to three- and four-body correlation functions. It is noted that the mode coupling contribution plays a similar role as that due to many-body correlation functions.

Role of many-body correlations in dynamics of liquids

A time correlation function is written exactly in terms of infinite series with each term containing contributions separately due to two, three, and higher body static correlations. For a time correlation function of force acting on a tagged particle, it is found that contributions due to two and three body static correlation functions are sufficient to understand dynamics of dense gases whereas at the triple point and in the glassy phase it is necessary to include contributions due to a four body correlation function.

Memory effect in friction on a particle caused by a system of fixed or moving scatterers with power law potential

The memory function for friction on a particle caused by a system of fixed or moving scatterers is evaluated for power law interaction. For a dilute system the study extends the steady-state calculation based on the Boltzmann equation to the case of frequency dependence due to the dynamics of the scattering process. For a dense gas an Enskog approximation can be used. The power law potential leads to scaling behavior of the dynamical friction coefficient as a function of reduced mass, coupling coefficient, and energy.

Binary and multiparticle contributions to the velocity autocorrelation function

A method for including the contribution of many-body correlation effects to the microscopically obtained results of the two-body contribution to the velocity autocorrelation has been proposed. A significant improvement over the results obtained through only binary contribution has been found, as can be judged by comparing the results for force and velocity autocorrelation functions of Lennard Jones fluids with that of molecular dynamic simulations. The agreement of results of self-diffusion coefficient is also quite good with simulation data over a wide range of densities and temperatures.

Shear viscosity of liquid mixtures: mass dependence

The expressions for zeroth, second, and fourth sum rules of the transverse stress autocorrelation function of a two-component fluid have been derived. These sum rules and Mori's memory function formalism have been used to study the shear viscosity of Ar-Kr and isotopic mixtures. It has been found that the theoretical result is in good agreement with the computer simulation result for the Ar-Kr mixture. The mass dependence of shear viscosity for different mole fractions shows that deviation from ideal linear model comes even from the mass difference in two species of the fluid mixture. At higher mass ratio, shear viscosity of the mixture is not explained by any of the empirical models.