The Landau phenomenological free-energy expansion in its discrete form is used to describe the free energy of each layer of a ferroelectric (FE) and antiferroelectric (AF) liquid crystalline system. In order to study systematically the effect of electric field on phases, a simple free-energy model is considered, which includes only the usual Van der Wools, nearest-neighbour and next nearest-neighbour interactions. Numerical simulation based on the discrete-form of Landau-Khalatnikov equations of motion is performed to analyze the influence of electric field on the system. The resultant structural changes are presented.