Crystallization and glass formation in hard ellipsoids

Schilling, T^1
1 University Mainz, Germany

Suspensions of hard objects such as spheres, cylinders or ellipsoids are useful model systems for basic questions of statistical mechanics. We present computer simulation studies on the crystalline phases and glassy dynamics of hard ellipsoids of revolution. For aspect ratios > 3 the previously suggested stretched-fcc phase [D. Frenkel and   B. M. Mulder, Mol. Phys. 55, 1171 (1985)] is replaced by a novel crystalline phase. The close-packed version of this crystal is a specimen of the family of superdense packings recently reported [Donev et al., Phys. Rev. Lett. 92, 255506 (2004)]. We also present evidence for glassy dynamics in suspensions of monodisperse hard ellipsoids. In equilibrium, almost spherical ellipsoids show a first order transition from an isotropic phase to a rotator phase. When overcompressing the isotropic phase into the rotator regime, we observe two-step relaxation in positional and orientational correlators, and super-Arrhenius slowing down of diffusion and relaxation. The effects are strong enough for asymptotic laws of mode-coupling theory to apply. Glassy dynamics are unusual in monodisperse systems. Typically, polydispersity in size or a mixture of particle species is prerequisite to prevent crystallization. Here, we show that a slight particle anisometry acts as a sufficient source of disorder.