Phase diagrams of charged colloidal particles

We have calculated the phase diagrams of charged colloidal particles in the parameter space. The free energies of different phases, which were used to determine the phase boundaries, were calculated variationally. The Einstein oscillators and the hard sphere fluid were used as the reference systems for the solid phases and the liquid, respectively. The interparticle interactions were approximated to be the Debye–Hückel screened Coulomb potential with size correction. We show that the solid phases are stable at low salt concentrations: bcc is preferred only at high charges and at low densities while fcc is dominant at higher densities. The solid phases melt upon the addition of salt: bcc may or may not transform to fcc before melting, depending on the particle number densities. No reentrant transition is found upon the addition of salt. When the particles are extremely highly charged, the system may undergo fcc–bcc–fcc transitions at nonzero salt concentration when the particle number density is increased.