PNNL

Abstract

Molecular dynamics simulation of the AgCl/KCl(aq) interfacial electrostatic capacity is presented. The simulations are motivated by the need to reduce ambiguities in the parameterization of conventional electrical double layer models, which here we attempt by determining the interfacial structure and charge distribution explicitly at the molecular level. Reduction of the interfacial molecular structure to conventional fixed plane models of the electrical double layer is shown. The calculated value of interfacial capacity ( ?F/cm2) is in agreement with experiment for the closely related AgI/electrolyte interface [4]. Capacity profiles determined by combining the molecularly-resolved interfacial structure and hypothetical planes of charge separation show a similar decay to the classical Helmholtz model. This proves that a rigid parallel-plate capacitor model gives a reasonable approximation of the interfacial capacity for the particular electrolyte concentration under consideration (0.72 mol/dm3). Furthermore, the dielectric constant for the first layer of adsorbed water is calculated to equal 5.1, which confirms that water near the charged interface is under dielectric saturation conditions.