  Light-induced ion demixing in mixed-halide perovskites is simulated
numerically using the phenomenological Cahn-Hilliard equation. In the model we
consider the energy of local elastic deformation as well as the contribution of
free carriers, assuming both the polaron and the bandgap-fluctuation models.
The simulation shows that elastic deformation suppresses the demixing while
free carriers promote it, however both effects lead to different ion
distributions. The free-carrier-induced demixing appears only for larger
starting random fluctuations of the ion concentration.
