Computer simulation of molten-salt interphases. Effect of a rigid boundary and an applied electric field

Abstract

The computer simulation technique of molecular dynamics has been used to investigate the microscopic boundary between a model of molten KCl and rigid, smooth walls above the bulk melting temperature and near zero pressure. A lamina model was employed with 288 or 504 ions in the basic cell replicated in two dimensions. Results were obtained for unperturbed films and also after allowing equilibration with externally applied electric fields (ca. 10⁷ V cm^–1). There was substantial structural ordering in the interphase broadly in agreement with current theories. The charge separation observed close to the electrified interfaces arose from only small changes in the time-averaged distribution of anions and cations at interphasial sites. The calculated double-layer capacitance is similar to experimental values at an ideally polarisable electrode. Thermodynamic properties were calculated and are discussed. There is evidence that the film thickness attainable was not sufficient to avoid interaction between the interphases. Other limitations of the current model are also discussed.