Fig. 3.

Density functional theory modeling of halide phase segregation. a Estimated free energy of formation as a function of bromide fraction x. The blue line/circles are generalized gradient approximation (GGA)-computed 0 K ground state formation energies, including spin-orbit coupling. The green line/squares are free energies of mixing at 300 K, assuming ideal mixing on the halide sublattice. The red line/inverted triangles represent the free energy difference after single photon absorption. All energies are reported per two formula units. Blue and pink shaded areas indicate positive (phase separation favored) and negative (phase separation disfavored) free energy regions. b Approximate size of separated domains, n _max, following single photon absorption