Cluster crystal formation in binary solutions with bounded interaction potentials

Abstract

In the course of this work, I have implemented a genetic algorithm, which can predict candidate crystal structures for binary systems of colloidal particles with bounded interaction potentials, which are able to form clusters of overlapping particles. The algorithm was utilized in combination with a minimization based on classical density functional theory to predict phase diagrams of binary cluster crystal systems.The system of interest is an equimolar mixture of two kinds of particles (labelled 1and 2). All interactions were assumed to be of the form of a generalized exponential model of order 4. The candidate crystal structures were restricted to be of the form of periodic lattices with Gaussian-shaped one-particle density profiles. The aim of this work is to investigate the changes in the phase diagram upon increasing the 12-interaction strength relative to equal 11- and 22- interaction strengths.The system was found to form two kinds of crystal structures (a BCC structure and an FCC/tetragonal structure), that can under go a first order structural phase transition.Upon increasing the 12-interaction strength the region in the phase diagram, where the BCC structure is stable, shrinks in size before completely vanishing out of the phase diagram. The FCC/tetragonal structure is an FCC structure for equal interaction strengths and transforms into a tetragonal structure as the 12-interaction increases.