Generating Ultradense Jammed Ellipse Packings Using Biased SWAP.

Using a Lubachevsky-Stillinger-like growth algorithm combined with biased SWAP Monte Carlo and transient degrees of freedom, we generate ultradense disordered jammed ellipse packings. For all aspect ratios α, these packings exhibit significantly smaller intermediate-wavelength density fluctuations and greater local nematic order than their less-dense counterparts. The densest packings are disordered despite having packing fractions ϕJ(α) that are within less than 0.5% of that of the monodisperse-ellipse crystal [ϕxtal = π/(2√3) ≃ 0.9069] over the range 1.2 ≲ α ≲ 1.45 and coordination numbers ZJ(α) that are within less than 0.5% of isostaticity [Ziso = 6] over the range 1.2 ≲ α ≲ 2.6. Lower-α packings are strongly fractionated and consist of polycrystals of intermediate-size particles, with the largest and smallest particles isolated at the grain boundaries. Higher-α packings are also fractionated, but in a qualitatively different fashion; they are composed─of increasingly large locally nematic domains─reminiscent of liquid glasses.