Progress in computer simulations of liquid crystals

Abstract

This article reviews some of the recent progress in the simulation of liquid crystals across a range of length and time scales. Simulators now have an extensive range of models at their disposal, ranging from fully atomistic studies where each atom is represented in a simulation, via hard or soft anisotropic potentials, to lattice models and director-based simulation methods. Each of these provide access to different phenomena. The progress towards accurate atomistic modelling of nematics is discussed in detail, pointing to improvements in force fields made recently and discussing the progress towards accurate prediction of material properties. Three material properties are discussed in detail: elastic constants, rotational viscosity and helical twisting powers. The simulation methods that can be employed to extract such properties are reviewed and the insights provided by recent results from atomistic and coarse-grained models are discussed. The article points also to the recent success of coarse-grained modelling in helping to understand the structure of complex macromolecular liquid crystals: liquid crystal polymers and liquid crystal dendrimers in which the macromolecules contain different types of interaction site. Finally, it is worth noting that throughout Nature liquid crystals occur as the archetypal self-assembled materials; able to form well-defined self-organized structures, which are often ordered at the nanoscale. With this in mind, some perspectives on the future use of these materials are presented, with suggestions for how liquid crystal simulation can be used to help in the design of the next generation of nanoscale devices. Contents PAGE 1. Introduction 422 2. Simulation of liquid crystals: crossing the time and length scales 423 3. Simulation models for liquid crystal phases 424 4. Progress in atomistic simulations 428 4.1. Force fields for atomistic simulation of liquid crystals 428 4.2. Prediction of transition temperatures and structure in nematic fluids 431 5. Calculation of materials properties for atomistic and mesoscale models 435 5.1. Elastic constants 435 5.2. Rotational viscosity 438 5.3. Helical twisting powers 439 6. Coarse-grained simulations for complex liquid crystalline materials 444 6.1. A coarse-grained model for flexible macromolecular liquid crystals 444 6.2. Liquid crystal polymers 446 6.3. Liquid crystal dendrimers 447 7. Some perspectives on the future 450 Acknowledgements 451 References 451