We study the mechanism of defect migration and the phase transitions of 3D colloidal crystals (CCA) using Langevin dynamics simulations. DLVO (Derjaguin and Landau, Verwey and Overbeek) pair potential has been applied. In the melting transition study we use the Voronoi volume and face analysis to describe the melting of a CCA system upon changing the effective charge and Debye length. We calculate the self diffusion coefficient of the colloid particles and the diffusion constant for vacancies as a function of temperature and the DLVO potential parameters, effective colloid charge and Debye length. We investigate the phase behavior of several systems with different interaction potential parameters using Voronoi analysis. Voronoi polyhedra tessellation, which is a useful method for characterizing the nearest neighbour environment around each atom, provides a way to identify phase transitions as well as topological and geometrical changes in crystals. We observe FCC crystal melting at larger values of inverse Debye length, for constant effective charge. Melting of the FCC also occurs at a constant Debye length as the effective particle
charge decreases. We also calculated the particle self diffusion coefficient as function of the interaction potential. At a constant Debye length the self diffusion coefficient increases upon decreasing the effective colloid charge. As expected from the behavior of a system which shows a phase transition from crystal phase to fluid phase, upon increasing the inverse Debye screening length, κσ, the diffusion coefficient also increases rapidly. Calculation of the ratio of the average amplitude of thermal vibrations to the nearest neighbor distances of the colloid particles in the CCA at different effective charges and inverse Debye lengths shows that the melting point we calculated using the Voronoi distribution of the number of Voronoi polygon faces and volumes is in very good agreement with the Lindemann criterion.
Langevin Dynamics Simulation of 3D Colloidal Crystal Vacancies and Phase Transitions. Rozita Laghaei, Sanford A. Asher and Rob D. Coalson J. Phys. Chem. B, 2013, 117, 5271–5279).
