Novel crystal phase in suspensions of hard ellipsoids

TL;DR

This study uses computer simulations to identify a new crystalline phase in suspensions of hard ellipsoids with aspect ratios ≥3, revealing a monoclinic structure with unique packing properties.

Contribution

It uncovers a novel monoclinic crystalline phase with two differently oriented ellipsoids, replacing the previously suggested phase for certain aspect ratios.

Findings

Discovery of a new monoclinic crystal structure.

Identification of a soft lattice angle beta.

Connection to superdense packings.

Abstract

We present a computer simulation study on the crystalline phases of hard ellipsoids of revolution. For aspect ratios greater than or equal to 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. Its unit cell contains two ellipsoids with unequal orientations. The lattice is simple monoclinic. The angle of inclination of the lattice, beta, is a very soft degree of freedom, while the two right angles are stiff. For one particular value of beta, 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)]. These results are relevant for studies of nucleation and glassy dynamics of colloidal suspensions of ellipsoids.