Novel Ground-State Crystals with Controlled Vacancy Concentrations: From Kagom\'{e} to Honeycomb to Stripes

TL;DR

This paper introduces a family of pair potentials that stabilize various vacancy-rich crystals as ground states, including kagomé, honeycomb, and stripe phases, with potential applications in colloidal and photonic materials.

Contribution

The authors develop a simple, short-range pair potential with a tunable parameter that stabilizes a diverse set of vacancy-containing crystal ground states, expanding the design space for novel materials.

Findings

Ground states include kagomé, honeycomb, and stripe crystals.

Ground states are mechanically stable but challenging to self-assemble.

Potential for experimental realization in colloidal and photonic systems.

Abstract

We introduce a one-parameter family, $0 \leq H \leq 1$, of pair potential functions with a single relative energy minimum that stabilize a range of vacancy-riddled crystals as ground states. The "quintic potential" is a short-ranged, nonnegative pair potential with a single local minimum of height $H$ at unit distance and vanishes cubically at a distance of $\rt$. We have developed this potential to produce ground states with the symmetry of the triangular lattice while favoring the presence of vacancies. After an exhaustive search using various optimization and simulation methods, we believe that we have determined the ground states for all pressures, densities, and $0 \leq H \leq 1$. For specific areas below $3\rt/2$, the ground states of the "quintic potential" include high-density and low-density triangular lattices, kagom\'{e} and honeycomb crystals, and stripes. We find that these ground states are mechanically stable but are difficult to self-assemble in computer simulations without defects. For specific areas above $3\rt/2$, these systems have a ground-state phase diagram that corresponds to hard disks with radius $\rt$. For the special case of H=0, a broad range of ground states is available. Analysis of this case suggests that among many ground states, a high-density triangular lattice, low-density triangular lattice, and striped phases have the highest entropy for certain densities. The simplicity of this potential makes it an attractive candidate for experimental realization with application to the development of novel colloidal crystals or photonic materials.