J.P.J. Michels

Molecular-dynamical calculations of the self-diffusion coefficient below the critical density

Abstract By means of a molecular dynamical method the self-diffusion coefficient of gaseous systems have been calculated at densities below the critical. It has been found that the attractive part of the intermolecular potential has a remarkable influence on the density dependence of diffusion. Moreover, short-time effects in the behaviour of the velocity autocorrelation function, due to attractive forces, have been detected.

The density dependence of the self-diffusion coefficient of krypton

Abstract The diffusion coefficient of 85 Kr in natural krypton has been measured as a function of density. The results deviate significantly from the values predicted by the Enskog theory. At low densities, the behaviour can be described by regarding the gas as a monomer—dimer mixture.

Extended hydrodynamic modes in a dense hard sphere fluid

Abstract A computer simulation experiment of a dense hard sphere fluid of 256 particles shows that the intermediate scattering function and the longitudinal velocity correlation function can be described by three extended hydrodynamic modes, the properties of which agree well with those predicted by the revised Enskog theory.

Molecular dynamical calculations on the viscosity of a square-well fluid

Abstract The coefficient of viscosity for a square-well fluid is calculated by molecular dynamics as a function of the well-depth for densities up to the region of the fluid-solid phase transition. The inclusion of an attractive contribution in the intermolecular potential has a profound influence on the behaviour of the viscosity coeffient and is also responsible for the qualitative correspondence with real systems which has been found for densities above the critical one.

Linear kinetic theory of the square-well fluid

A recently proposed kinetic theory for a dense fluid of square-well particles is linearised and shown to satisfy time-reversal symmetry. The hydrodynamic modes and their extensions to short wavelengths are calculated with the aid of equilibrium correlation functions which are taken from molecular dynamics simulations and are presented as well. Under most conditions, potential energy fluctuations decay slowly in comparison with velocity fluctuations.

The influence of the attractive part of the Lennard-Jones potential on the viscosity

Abstract Molecular dynamics studies of Lennard-Jones repulsive and full potential systems have shown that the attractive portion of the potential has a small effect on the viscosity in comparison to the effect of an attractive square well superimposed on a hard-sphere potential. This indicates the importance of the precise shape of the attractive force on the viscosity.

Long time tails in two-dimensional Lennard-Jones systems

Abstract Studies of two-dimensional Lennard-Jones repulsive and full potential systems have shown that the long time tails of the velocity autocorrelation function of the repulsive systems are in agreement with Enskog predictions. Moreover, the full systems display similar behavior although the tail coefficient is smaller.

The short-time behavior of the velocity autocorrelation function of smooth, hard hyperspheres in three, four and five dimensions

Abstract The short-time behavior of the velocity autocorrelation function of smooth, hard hyperspheres in three, four and five dimensions obtained from molecular dynamic simulations is in excellent agreement with the predictions of Enskog theory.

Distribution of free flight times in a hard sphere gas

Using a simple functional relation the distribution of the times of free flight in a classical gas of hard spheres is shown to depend only on two specific combinations of the molecular and thermodynamic parameter. This distribution has been calculated with molecular dynamics for three values of the density. The behaviour of the function is found to be qualitatively similar to its form in the low density limit, even for densities for which the system is far into the crystalline phase.

On the coordination number of self-avoiding two-dimensional random walks

Abstract A numerical value for the effective coordination number of self-avoiding random walks has recently been obtained by analytical considerations. This value differs considerably from the empirical value obtained by computer simulations. It turns out that a seemingly severe simplification in the analytical approach is not the first cause of this discrepancy.