Calculations of the Structure of Basin Volumes for Mechanically Stable Packings

TL;DR

This paper introduces a new computational method to predict the probabilities of mechanically stable packings in granular systems by measuring their basin volumes, revealing that probabilities are influenced by complex geometric features rather than core sizes.

Contribution

The authors develop a novel approach to calculate MS packing probabilities through basin volume measurement, highlighting the role of distant geometric features in these probabilities.

Findings

MS packing probabilities are weakly correlated with core volumes.

Distant geometric features significantly influence packing probabilities.

A small core region exists around each MS packing in configuration space.

Abstract

There are a finite number of distinct mechanically stable (MS) packings in model granular systems composed of frictionless spherical grains. For typical packing-generation protocols employed in experimental and numerical studies, the probabilities with which the MS packings occur are highly nonuniform and depend strongly on parameters in the protocol. Despite intense work, it is extremely difficult to predict {\it a priori} the MS packing probabilities, or even which MS packings will be the most versus the least probable. We describe a novel computational method for calculating the MS packing probabilities by directly measuring the volume of the MS packing `basin of attraction', which we define as the collection of initial points in configuration space at {\it zero packing fraction} that map to a given MS packing by following a particular dynamics in the density landscape. We show that there is a small core region with volume $V^c_n$ surrounding each MS packing $n$ in configuration space in which all initial conditions map to a given MS packing. However, we find that the MS packing probabilities are very weakly correlated with core volumes. Instead, MS packing probabilities obtained using initially dilute configurations are determined by complex geometric features of the basin of attraction that are distant from the MS packing.