Electrostatics of Phase Boundaries in Coulomb systems

Any interface boundary in an equilibrium system of Coulomb particles is accompanied by the existence of a finite difference in the average electrostatic potential through this boundary. The discussed interface potential drop is a thermodynamic quantity. It depends on temperature only and does not depend on surface properties. The zero-temperature limit of this drop (along the coexistence curve) is an individual substance coefficient. At high temperature the drop tends to zero at critical point of gasliquid phase transition. A special critical exponent can be defined to describe this behavior. Study of the interface potential drop is illuminative in simplified Coulomb models: i.e. for melting and evaporation in variants of One Component Plasma model (OCP), or for model of Charged Hard/Soft Spheres (CHS/CSS) etc. In all these cases properties of the potential drop can be easily calculated by the DNS methods (direct numerical simulation) when the two-phase coexistence in Coulomb system is really simulated. Electrostatics of phase boundaries in real systems could be elucidated in analytical calculation of two-phase coexistence via finite-temperature DFT approach (density functional theory).