Onsager’s Wien effect on a lattice

Abstract

The nonlinear response of a weak electrolyte to an applied electric field is known as the Wien effect. This is now simulated on a lattice Coulomb gas, therefore providing a platform for investigating system-specific corrections to the firmly established theory accounting for it. The second Wien effect describes the nonlinear, non-equilibrium response of a weak electrolyte in moderate to high electric fields. Onsager’s 1934 electrodiffusion theory1, along with various extensions2,3,4, has been invoked for systems and phenomena as diverse as solar cells5,6, surfactant solutions7, water splitting reactions8,9, dielectric liquids10, electrohydrodynamic flow11, water and ice physics12, electrical double layers13, non-ohmic conduction in semiconductors14 and oxide glasses15, biochemical nerve response16 and magnetic monopoles in spin ice17. In view of this technological importance and the experimental ubiquity of such phenomena, it is surprising that Onsager’s Wien effect has never been studied by numerical simulation. Here we present simulations of a lattice Coulomb gas, treating the widely applicable case of a double equilibrium for free charge generation. We obtain detailed characterization of the Wien effect and confirm the accuracy of the analytical theories as regards the field evolution of the free charge density and correlations. We also demonstrate that simulations can uncover further corrections, such as how the field-dependent conductivity may be influenced by details of microscopic dynamics. We conclude that lattice simulation offers a powerful means by which to model and investigate system-specific corrections to the Onsager theory, and thus constitutes a valuable tool for detailed theoretical studies of the numerous practical applications of the second Wien effect.