Programming patchy particles to form complex periodic structures

TL;DR

This paper presents a method to design patchy particles with specific interactions, including torsional constraints, enabling them to reliably self-assemble into complex periodic crystal structures, including large unit cell clathrates.

Contribution

It introduces a novel design scheme incorporating torsional components to guide particles into complex target crystal structures with high fidelity.

Findings

Target crystals are the global free-energy minima at low temperatures.

Complex structures like a 46-particle clathrate can assemble from a fluid phase.

Reducing interaction specificity can lead to alternative structures, but complex designs remain robust.

Abstract

We introduce a scheme to design patchy particles so that a given target crystal is the global free-energy minimum at sufficiently low temperature. A key feature is a torsional component to the potential that only allows binding when particles have the correct relative orientations. In all examples studied, the target crystal structures readily assembled on annealing from a low-density fluid phase, albeit with the simpler target structures assembling more rapidly. The most complex example was a clathrate with 46 particles in its primitive unit cell. We also explored whether the structural information encoded in the particle interactions could be further reduced. For example, removing the torsional restrictions led to the assembly of an alternative crystal structure for the BC8-forming design, but the more complex clathrate design was still able to assemble because of the greater remaining specificity.