On energy formulations of electrostatics for continuum media

In this paper we present a unified energy formulation of electrostatics for continuum media including conductors, dielectrics, ferroelectrics, etc. The effects of boundary devices, external charges and polarizations are taken into account in formulating the free energy. We further explore the relations between various energy formulations including Landau–Ginzburg–Devonshire's formulation, Toupin's formulation, Ericksen's formulation, formulations with respect to a change of comparison or background medium, a formulation without introducing the quantity of polarization, and the Hashin–Shtrikman variational principle. Finally, we apply the formulation to calculate the effective free energy of a polarizable body in the proximity of a conductor, and to estimate the effective properties of nonlinear dielectric composites. We expect that this formulation and clarification will provide a solid ground for addressing electro-elastics of deformable bodies.