Crystallization of nanoparticles with square-shoulder interactions

Abstract

Complex structures in colloidal systems are often stabilized by a competition between different length scales. Inspired by recent experiments on nanoparticles coated with polymers, we use Monte Carlo simulations to explore the types of crystal structures that can form in a simple (square shoulder) model which explicitly incorporates two favored distances between the particles. To this end, we implement a Monte Carlo-based crystal structure finding algorithm, and use it to explore the types of crystal structure we may expect this system to form, as a function of the interaction range and strength. The aim is to identify sets of interaction parameters where complex crystal structures (such as the C14 lattice) can be expected to form. Although we do not observe the C14 lattice in this model, a range of new crystal structures are classified. We use cell theory to calculate the free energy of the obtained structures and predict phase diagrams for different interaction ranges.