Study On Ferroelectric Phases Of The Elongation Dipoles

The investigations on the soft matter are the important branch in the field of physics in the 21st Century. The dipole fluid system researched in this thesis belongs to a kind of soft matter. The research on the dipolar fluid system possesses the vital significance. The strongly interacting dipoles can form orientational orderly liquid crystal phases. However, the most of the computer simulations adopt the point dipole model in previous research. This thesis will use elongation dipole model to describe the structure and phase behavior of the system in order to approach to the real situation. Moreover we research the impact of temperature to the system.Firstly, the thesis introduces the concepts of soft material, liquid crystal and dipolar fluid, and describes in detail the characteristics of soft material and the research significance of soft matter, meanwhile focuses on this soft liquid crystal material and illustrates the unique properties of liquid crystal. Secondly, the computer simulation approach is introduced, focusing on the molecular dynamics simulation methods, such as solving equations of motion of the finite difference method, the interaction potential between atoms, balanced ensemble and so on. Finally, we studied a model system consisting of elongation dipole by Molecular Dynamics simulation. The potential of system consist of LJ potential and Coulomb potential. In consideration of a more complex system such model has some innovative, and the result is more accurate. We analyze the simulation results using the orientational order parameters, mean square displacement and the vertical and horizontal radial distribution function. The results were more reliable. In addition, we study the impact of temperature on the phase transition. The main conclusions are outlined as follows:1. By studying the orientational order parameters, we find out anti-ferroelectric liquid crystals turning point. At the density of 0.362 kg/m~3, the turning point is 0.082nm.2. By studying the vertical and horizontal radial distribution function, we verified the order and related in the fluid system. In size=0.05nm, we find that the vertical radial distribution function is long range order, and the horizontal radial distribution function is disorder.3. The impact of temperature on the system, we conclude that as the temperature increases, the antiferroelectric phase transform gradually to ferroelectric phase.