Modelistic approach to structure and dynamics of soft matter

The aim of this work is the study of the reliability of novel approaches for the modeling of soft matter systems, in particular of liquid crystals. After a brief introduction to these systems in Chapter 1, the validation of a protocol for force field parameterization is presented in Chapter 2. This protocol was developed by the Pisa group of Liquid Crystals in 2002 and consists of the derivation of both inter and intramolecular contributions to the potential from quantum mechanical data. First, the energies of various dimer configurations and of some monomer conformations are computed at suitable levels of theory. Then, parametric model functions representing intra and intermolecular energies are fitted on these databases and parameters are derived. Finally, the force field is tested in molecular simulation runs and simulated and experimental properties are compared to assess the quality of the obtained force field. In Chapter 2 this approach is tested on a mesogenic molecule, namely 4,4'-diheptylazoxybenzene, making use of an united atom model, while in Chapter 3 the same validation is performed at a higher resolution with a fully atomistic approach. This investigation has allowed a deeper insight into the strong and weak points of the approach and has led to an improved strategy where the force field is derived from quantum mechanical energies of dimer configurations selected with the help of molecular simulations. The latest development of this improved strategy is presented in Chapter 4: a Fortran code, named PICKY, is being developed and its beta version has been tested on a simple molecule as a test case. Finally, Chapter 5 presents a further tool for investigations at atomistic level of details. It is a Fortran code, named POLDO, for exploring the energy minima of the potential energy surface of large and flexible van der Waals dimers.