Physics (Internal)

Are Mechanically Stable Hard Particle Packings Equally Likely?

This event is part of the Biophysics/Condensed Matter Seminar Series.

There have been several attempts to construct statistical mechanical descriptions of athermal particulate systems, for example the Edward’s entropy description for granular materials. Tapping experiments by Nowak, et al. (Phys. Rev. E, 57 (1998) 1971) and numerical simulations of granular shear flow by Makse, et al. (Nature 415 (2002) 614) have shown that the Edward’s description may be promising for slow, dense granular flows. An essential assumption of the Edward’s framework is that all jammed configurations are equally likely. However, this assumption has not been explicitly tested. Using numerical simulations, we create jammed hard particle packings using two experimentally relevant protocols: 1) a compression and decompression scheme and 2) quasi-static shear flow at constant pressure. For both methods, we find that jammed packings are not equally likely, and thus we argue that the Edward’s entropy description for granular materials should be reconsidered.