Dense particle packings have served as useful models of the structures of liquid, glassy and crystalline states of matter1,2,3,4, granular media3,5, heterogeneous materials3 and biological systems6,7,8. Probing the symmetries and other mathematical properties of the densest packings is a problem of interest in discrete geometry and number theory9,10,11. Previous work has focused mainly on spherical particles—very little is known about dense polyhedral packings. Here we formulate the generation of dense packings of polyhedra as an optimization problem, using an adaptive fundamental cell subject to periodic boundary conditions (we term this the ‘adaptive shrinking cell’ scheme). Using a variety of multi-particle initial configurations, we find the densest known packings of the four non-tiling Platonic solids (the tetrahedron, octahedron, dodecahedron and icosahedron) in three-dimensional Euclidean space. The densities are 0.782…, 0.947…, 0.904... and 0.836..., respectively. Unlike the densest tetrahedral packing, which must not be a Bravais lattice packing, the densest packings of the other non-tiling Platonic solids that we obtain are their previously known optimal (Bravais) lattice packings. Combining our simulation results with derived rigorous upper bounds and theoretical arguments leads us to the conjecture that the densest packings of the Platonic and Archimedean solids with central symmetry are given by their corresponding densest lattice packings. This is the analogue of Kepler’s sphere conjecture for these solids.
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We are grateful to H. Cohn and J. Conway for comments on our manuscript. S.T. thanks the Institute for Advanced Study for its hospitality during his stay there. This work was supported by the National Science Foundation under award numbers DMS-0804431 and DMR-0820341. The figures showing the polyhedra were generated using the AntiPrism package developed by A. Rossiter.
Author Contributions S.T. devised the algorithm and upper bounds, performed theoretical analysis, and wrote the paper. Y.J. implemented the algorithm, performed theoretical analysis, commented on the manuscript and created all of the figures.
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Torquato, S., Jiao, Y. Dense packings of the Platonic and Archimedean solids. Nature 460, 876–879 (2009) doi:10.1038/nature08239
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