Molecular dynamics simulation of gaseous ion-motion in electrostatic fields

Abstract

A molecular dynamics (MD) method has been developed for the simulation of the motion of ions in neutral gases under the influence of homogeneous electrostatic fields. The method treats the translational motion of the ions and gas molecules classically and thus requires as input the ion–molecule interaction potentials. The continuous dissipation of a part of the ion-energy to a thermal bath is accomplished through the introduction of ‘‘iconical interactions’’ between ions and images of the neutrals created and stored in the memory of a computer during ion–atom encounters. The steady ion motion is then simulated by usual equilibrium MD methods using periodic boundary conditions. The resulting ion mobilities, effective temperatures, and third other velocity-distribution moments, expressed as skewness parameters, compare well with available results derived from the moment solution of Boltzmann equation and Monte Carlo simulations using the same interaction potentials in the cases of K+ in He and Ar, as well as of Ba+ in Ar. The additional reproduction of experimental data provides an independent test for the accuracy of the employed model potentials. Although the method has been applied to atomic systems it is easily extendable to the more complex molecular systems but at the expense of computer time.