Molecular Dynamics Simulation of the AgCl/Electrolyte Interfacial Capacity

Molecular dynamics simulation of the AgCl(100)/KCl(aq) interfacial electrostatic capacity is presented. The simulations are motivated by the need to reduce ambiguities in electrical double layer model parametrization, which here we attempt by reducing the computed interfacial molecular structure to hypothetical planes of charge separation consistent with a treatment of the interface in terms of parallel plate capacitors. The calculated interfacial capacity (c(int) = 8.43 mu F/cm(2)) is in excellent agreement with measurements for the closely related Agl/electrolyte interface, and the dependence on electrolyte concentration and temperature are qualitatively similar to experimental observations. Molecular dynamics based capacity profiles show a similar overall decay to the classical Helmholtz model, validating its use for approximating the interfacial capacity at relatively high electrolyte concentration. However, fine structure is present and the interfacial electrostatic properties oscillate with distance from the surface. The dielectric constant for first layer water is calculated to equal 5.1, which confirms that water nearest the interface is under dielectric saturation conditions,