New High-Density Packings of Similarly Sized Binary Spheres

Binary sphere packings with a density greater than that of phase-separated face-centered cubic (fcc) packings are important structural candidates for the self-assembly of mixtures of stabilized, hard, spherical particles. Details are presented of an A3B binary hard sphere packing obtained by simulated annealing in an isopointal set 62cd/c. The structure has a higher density than all known others when the sphere radius ratio rA/rB is between 0.619 and 0.659786. This extends the known range over which compound binary sphere packings can exceed the density of phase-separated fcc packing. Previously, no packings were known to exceed this mark between a radius ratio of 0.62 and 1.0. The structure of interest has a peak density of 0.747857, which occurs at a radius ratio of 0.647989. A related dense packing is also discussed, which has a peak density of 0.7573 at a size ratio of 0.5147. This latter structure is the densest known noninterstitial compound packing when the mixture has three small spheres for every...