Computer Simulations provide an essential set of tools for the understanding of the macroscopic properties of liquid crystals and of their phase transitions in terms of molecular models. While simulations of liquid crystals are based on the same general Monte Carlo and Molecular Dynamics techniques used for other fluids, they present a number of specific problems and peculiarities connected with the intrinsic properties of these mesophases. An example is the need to develop suitable algorithms to calculate anisotropic static properties such as order parameters and tensorial observables as well as dynamic quantities like diffusion tensors, viscosities, susceptivities etc. Another series of problems is connected with the need of predicting the properties of liquid crystals from molecular models. This involves the determination of phase transitions and their characteristics, and requires on one hand the development of intermolecular potentials for modelling the essential molecular features of mesogens, and on the other performing large scale simulations, with a number of particles often an order of magnitude greater than those used for simple fluids. Such large numbers require exploiting state of the art resources in computing, and particularly parallel techniques with the development of appropriate algorithms. Further peculiarities of liquid crystals, compared to ordinary isotropic fluids, are their topological defects and it is now becoming feasible to simulate their core structure and optical textures. Similar methods can even be used to perform direct microscopic level simulations of simple devices and displays.
The field of computer simulations of anisotropic fluids is clearly interdisciplinary and evolving very rapidly and this has brought us to organize the NATO Advanced School Institute (ASI) on Advances in the Computer Simulations of Liquid Crystals, held at the Ettore Majorana Centre of Scientific culture (CCSEM) in Erice, Sicily from June 11th to June 21st, 1998. The School, that has tried to cover all the above issues considering various techniques and model systems (from lattice to hard particle and Gay-Berne up to atomistic) for thermotropics, lyotropics and some liquid crystals of biological interest has had an excellent panel of international Lecturers and has attracted over 70 very keen students and young researchers from different disciplines and 16 countries. The successful organization of the NATO ASI was only possible thanks to the help of many people and we would like to mention particularly our collaborators R. Berardi, A. Porreca, S. Orlandi and the competent and helpful staff of CCSEM. A particular thought is due to the memory of Dr. Alberto Gabriele, in charge of organization at the Centre, whose efficiency together with kindness, courtesy and dedication to CCSEM we had the fortune to appreciate.
The present book contains a large part of the lectures given at the NATO ASI starting with some introductory papers followed by more applicative and technical chapters. We believe it provides a timely account of the techniques and problems in the field and we hope it will convey some of the stimulating atmosphere of the School.
We are particularly grateful to the Lecturers, the members of the Scientific Committee, Professors N.A. Clark, G.R. Luckhurst, D. Frenkel and to the CCSEM Director, Professor A. Zichichi. We wish to thank NATO and its Science Committee for their essential support which made the organization of the School and the production of this book possible. We also acknowledge financial contributions from Ente per le Nuove tecnologie, l'Energia e l'Ambiente (ENEA), Consorzio Interuniversitario per la Chimica dei Materiali (now INSTM), TECDIS S.p.A., Consiglio Nazionale delle Ricerche (CNR) and Quadrics Supercomputers World (QSW).
Paolo Pasini Claudio Zannoni
INFN, Bologna Università di Bologna