Electroslatie Contribution to the Distortion Free Energy Density of Ferroelectric Liquid Crystals

In a chiral smectic C liquid crystal, a bend type deformation of the C-director induces a polarization charge. We have shown that due to the screening effect by impurity ions the free energy of the electrostatic interaction of the polarization charge is renormalized into the distortion free energy density associated with the bend mode of the C-director. The renormalized elastic constant depends on the electrostatic screening length (i.e., the amount of impurity ions) as well as on the magnitude of the spontaneous polarization.