D.L. Jolly

An efficient microcanonical sampling method

Abstract A new microcanonical sampling procedure is presented which incorporates much of the simplicity and efficiency of the canonical procedures. Comparison with previous procedures indicates that the gain in efficiency is substantial. The relevance to numerical simulation of rate processes and equilibrium systems is noted.

Ergodic collision theory of intermolecular energy transfer

Abstract We present a simple theory of collisional energy transfer between molecules based on the assumption of ergodic collisions, i.e., the final state distri

Molecular dynamics simulation of the mutual and self diffusion coefficients in Lennard-Jones liquid mixtures

A molecular dynamics calculation has been attempted for the mutual diffusion coefficient in a Lennard-Jones liquid mixture utilizing about 200 000 timesteps and incorporating the contribution for the thermodynamic factor. The precision of the result is about 8 per cent, excluding errors arising from the N dependence of the coefficient. For the same mixture, a number of calculations have been made for the self diffusion coefficients D 1 and D 2 varying the total number of particles. A significant apparent N dependence is noted for D 1 and D 2 individually but the ration D 1/D 2 is constant.

Hard dumbells: Monte Carlo pressures and virial coefficients

The equation of state was determined by Monte Carlo simulation for 108 dumb-bells subject to periodic boundary conditions. The isotropic fluid-solid phase transition was observed. An orientational phase transition was not observed. Virial coefficients through B5 were calculated.

Mass dependence of the self diffusion coefficients in two equimolar binary liquid Lennard-Jones systems determined through molecular dynamics simulation

Careful molecular dynamics simulations have been made on the mass dependence of the self diffusion coefficients of two liquid Lennard-Jones systems corresponding, respectively, to equimolar solutions of ‘argon(1)-argon(2)’ and ‘argon(1)-krypton(2)’. In each case the mass m 1 of component 1 was held at 39·948 amu, and the mass m 2 of component 2 was varied over a wide range, holding constant the potential parameters, mole fractions, density and temperature. The linear contributions to the slopes of the curves in a log-log plot of the diffusion coefficients versus m 2/m 1 were found to be of the order of -0·25. This was justified heuristically and, in the ‘argon-argon’ case, on the basis of a perturbation theory developed by Ebbsjo and collaborators. The analogous linear contributions for the diffusion coefficient ratios D 1/D 2 in a log-log plot versus m 2/m 1, were found to be much weaker, 0·064 and 0·075, respectively.

Simulation of microscopic chemical processes.: I. De-energization of bromine in argon

Abstract This is the first in a series of articles devoted to the study of fundamental chemical processes by numerical simulation. The main aim of this work is to facilitate the development of accurate chemical reaction rate theories. We report here the results of an investigation of the collisional de-energization of highly vibrationally excited bromine by a heatbath of argon atoms at 295 K. A molecular dynamics calculation has been carried out for a cell containing one bromine molecule and 106 argon atoms at pressures of about 20 and 100 atmospheres. On the average the bromine molecule loses about 0.4 kcal/mole per collision but the relaxation is dominated by collisions removing about 3 kcal/mole. Detailed statistics on the energy transfer including collision lifetimes and their correlation with the strength of the collision is provided. Comparing the relaxation rate for the two pressures we find a 20% deviation from the binary collision scaling law.

Ergodic collision theory of intermolecular energy transfer II. Quantum effects in the harmonic approximation

Abstract An efficient numerical implementation of the ergodic collision theory is described and used to evaluate the average energy transfer per collision relevant to several reactant species undergoing unimolecular reaction. The full effect due to vibrational quantization in the harmonic approximation is included and found to cause only a minor shift in the results previously obtained in a quasi-classical approximation. A much simplified computational method based on the use of specific heat data for the molecules concerned is suggested and shown to account for most of this shift.

Simulation of microscopic chemical processes.: II. De-energization of bromine in argon at high pressures

Abstract The collisional de-energization of very highly vibrationally excited bromine in an argon medium has been studied by molecular dynamics calculation at 295 K and pressures up to 1200 atm. This note is concerned, in particular, with the validity of the scaling laws for the relaxation rate obtained on the basis of the independent binary collision theory. The relaxation rate is found to increase faster than predicted by independent binary collision theory so that the deviation at 1200 atm amounts to a factor of two.

Equation of state of heteronuclear hard dumbbells

Abstract The equation of state of five heteronuclear dumbbells has been calculated by standard Monte Carlo techniques. Approximate theories are also used to calculate the equation of state and are compared to the “simulation” results.

Simulation of microscopic chemical processes. III. Deactivation and dissociation of bromine in argon at high pressure

Abstract Previous numerical simulation of the vibrational relaxation of highly excited bromine in argon at different pressures is here extended in several ways.