Frustration in glass-forming liquids and the breakdown of the Stokes-Einstein relation

The properties of a frustrated system which combines features of a spin gla ss and a lattice gas model are review ed. This system in one limit reproduc es the spin glass model, and in another limit coincides with a frustrated l attice gas model which displays glassy behaviour at high density or low tem perature. Tn mean field the static properties are closely related to those of the p-spin glass models. These models have recently received renewed att ention, as their dynamical behaviour in mean field is described by the same equations as those of the mode coupling theory for simple liquids. We argu e that also the frustrated lattice gas model may be described by the same e quations. We therefore expect in mean field a dynamical transition with a d iffusion coefficient vanishing with a power law. Compared to the p-spin mod el the frustrated lattice gas model has the advantage of being made of part icles, and therefore is more appropriate to describe a supercooled liquid. In particular it is possible to investigate the behaviour of the diffusion coefficient. Numerical simulation in 3 dimensions shows indeed that the dif fusion coefficient D approaches zero where the relaxation time diverges. Mo reover at low temperature the model exhibits a breakdown of the Stokes-Eins tein relation, in good agreement with recent experimental results on superc ooled orthoterphenyl.