EQUILIBRIUM EQUATIONS FOR PIEZOELECTRIC AND FERROELECTRIC MATERIALS

A continuum description of media characterized by intermolecular force s with short- and long-range contributions is presented. By means of a simple version of the density functional theory we derive equilibrium equations, whose solutions are stable deformed states. They reduce to the usual Euler-Lagrange equations only if the long-range part of the interaction can be neglected. These equations are used for the descri ption of piezoelectric and ferroelectric media. Lyotropic nematic liqu id crystals doped with magnetic grains are also considered by means of a simple model. [S0163-1829(98)00729-2].