Density-functional study of the cubic-to-rhombohedral transition in α-AlF₃

Under heating, α-AlF₃ undergoes a structural phase transition from rhombohedral to cubic at temperature T around 730 K. The density-functional method is used to examine the T = 0 energy surface in the structural parameter space, and finds the minimum in good agreement with the observed rhombohedral structure. The energy surface and electronic wave functions at the minimum are then used to calculate properties including density of states, Γ-point phonon modes, and the dielectric function. The dipole formed at each fluorine ion in the low-temperature phase is also calculated, and is used in a classical electrostatic picture to examine possible antiferroelectric aspects of this phase transition.