A Phenomenological Theory of Ferroelectric and Antiferroelectric Liquid Crystals Based on a Discrete Model

A discrete model of ferroelectric and antiferroelectric phases, which takes into account the molecular interactions up to the second-nearest neighbors, has been proposed. On the basis of the model the dispersion relation of normal modes and the temperature dependence of the helical pitch for four types of phase sequence are obtained. It is clarified that the experimentally observed phenomena such as the reverse of the helical sense at the SmC * -SmC A * transition point and the divergence of pitch in the SmC A * phase are caused by the chiral interactions between layers.