PPT Slide
Figures 5 and 6 show snapshots of the simulated system after equilibration for a =1.0 and a=0.01 respectively. For a =1.0 as the denstiy of the system is decreased the crystal structures melt. At lower densities small number of ‘B’ particles appear in the bulk of ‘A’ particles. Symmetrically small number of ‘A’ particles appear in the bulk of ‘B’ particles. This number increases as the density decreases further and, finally, the two species mix completely. This behavior is called as fluid-fluid phase transition. We have observed it for all the simulations where a?0.1.
For a =0.01 the situation is quite different. Mixing of the particles is observed before melting takes place. Therefore even after mixing the system is still a crystal. We call this type of phase transition as crystal-crystal phase transition.
Figures 7 and 8 show the correlation functions for fluid-fluid and crystal-crystal phase transition. ‘g11’ and ‘g12’ are the radial distribution functions for the same and different species respectively. Each plot contains radial distribution functions for three different values of density, corresponding to completely mixed, partially mixed and demixed states.
In the fluid-fluid transition case the radial distribution functions clearly show the melting of the system. The long range order is lost upon melting. When we look at the radial distribution functions for the demixed state we observe two different behaviors. For g11 the short range correlation are more dominant compared to the long range correlation, whereas for g12 long range correlation are more dominant. As the system mixes this behavior disappears, namely, the fluid homogenizes.
Radial distribution functions in figure 8 show several peaks for all densities, which clearly indicates that the system is crystal. The clear indication of mixing in g12 is the increasing amplitude of the first peak, as the system mixes. For g11 the amplitudes of the peaks decreases rapidly, as a result of mixing.