Abstract
The successive phase transitions in ferro- and antiferro-electric smetics have been discussed on the bases of the ANNNI model with the third next nearest neighbour interaction. Here, the nearest neighbour interacting modeh with variables indicating the sense of the molecular long axis is introduced to certify that model. By taking the summation over all states of these variables in the partition function the system is transformed into the effective Hamiltonian with long range interactions and many body forces. In the minimal theory where the range of the interaction is taken into account up to the third nearest neighbour, the assumptions appearing in the above ANNNI model are justified. In the intermediate phases excerpt for SmC* and SmCA* the ordering of the molecular sense is shown to be induced by the bias due to the order of layer stacking.
