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Models and Monte Carlo Simulations of Anisotropic Systems


Researchers: Cesare Chiccoli, Paolo Pasini


The main interest of this research field is to develop models and computational methods to study problems of relevance in statistical physics and condensed matter, devoting particular attention to the anisotropic systems. We use Monte Carlo simulations of lattice spin models that provide an interesting and useful approach for investigating various aspects of the physics of liquid crystals  both from a theoretical point of view and to analyze experimental data. These models can also suggest new experiments and contribute to study technological applications. In particular, mainly due to the simplicity of the models and consequently to the larger number of particles which can be treated in comparison with more realistic potentials, they also allow to tackle by computer simulations problems not easily accessible by theoretical approaches. The research involves the study of phase transitions in two an three dimensions for uniaxial and biaxial models, the study of confined systems (films, droplets) and the study  of the creation and evolution of topological defects induced by the confinement, by the boundary conditions and by other physical parameters such as, for example, the elastic constants. In addition to thermodynamic observables attempts are made to simulate experimental observables like NMR spectral lines  and polarized microscopy  images  to  better understand the real data and the orientational order inside the systems under investigation or to predict new experimental results. The study of the topological defects is of fundamental and applicative interest, being   a crucial aspect to be considered  in the construction of various electro-optical devices such as displays or waveguides.

Example of topological defects in a droplet formed by biaxial molecules: increasing the molecular biaxiality the size of the ring defect produced in the center by the long axis increases and then disclinations formed by the short axis appear.