Invited Lecture. Columnar ordering as an excluded-volume effect

The nature of the possible liquid-crystalline phases that a molecular or colloidal system may exhibit depends sensitively on the shape of the constituent particles. Recent computer simulations on fluids of consisting of non-spherical hard-core molecules suggest that, in order to predict the relative stability of isotropic, nematic, smectic and columnar phases in such very simple model fluids, it is not enough to characterize the molecular shape by an overall length-to-width ratio. New results of computer simulations on a model for disc-like molecules clearly illustrate this point.