For the 3-D version, where the density of the fcc can be beaten using ellipsoids, see A. Donev, I. Cisse, D. Sachs, E. A. Variano, F. H. Stillinger, R. Connelly, S. Torquato, and P. M. Chaikin, Improving the Density of Jammed Disordered Packings using Ellipsoids, Science, 303, 990-993 (2004). A. Donev, F. H. Stillinger, P. M. Chaikin, and S. Torquato, Unusually Dense Crystal Ellipsoid Packings, Physical Review Letters, 92, 255506 (2004). Neil