Molecular theory of layer contraction in smectic liquid crystals

The period of the layered structure in smectic A and smectic C liquid crystal phases has been calculated numerically by direct minimization of the mean-field free energy which takes into account the interaction between molecules in adjacent smectic layers. The smectic layer spacing is calculated for two systems characterized by conventional and anomalously weak layer contraction in the smectic C phase. It is then compared with the simple estimate based on the average projection of the molecular long axis on the smectic layer normal. For both systems, temperature variation of the average molecular projection is qualitatively similar to that of the calculated layer spacing although certain quantitative deviations exist.