Adam B. Hopkins, Frank H. Stillinger, Salvatore Torquato
The densest binary sphere packings in the alpha-x plane of small to large
sphere radius ratio alpha and small sphere relative concentration x have
historically been very difficult to determine. Previous research had led to the
prediction that these packings were composed of a few known "alloy" phases
including, for example, the AlB2 (hexagonal omega), HgBr2, and AuTe2
structures, and to XYn structures composed of close-packed large spheres with
small spheres (in a number ratio of n to 1) in the interstices, e.g., the NaCl
packing for n = 1. However, utilizing an implementation of the Torquato-Jiao
sphere-packing algorithm [S. Torquato and Y. Jiao, Phys. Rev. E 82, 061302
(2010)], we have discovered that many more structures appear in the densest
packings. For example, while all previously known densest structures were
composed of spheres in small to large number ratios of one to one, two to one,
and very recently three to one, we have identified densest structures with
number ratios of seven to three and five to two. In a recent work [A. B.
Hopkins, Y. Jiao, F. H. Stillinger, and S. Torquato, Phys. Rev. Lett. 107,
125501 (2011)], we summarized these findings. In this work, we present the
structures of the densest-known packings and provide details about their
characteristics. Our findings demonstrate that a broad array of different
densest mechanically stable structures consisting of only two types of
components can form without any consideration of attractive or anisotropic
interactions. In addition, the novel structures that we have identified may
correspond to currently unidentified stable phases of certain binary atomic and
molecular systems, particularly at high temperatures and pressures.
View original:
http://arxiv.org/abs/1111.4917
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