  We report on optical properties of various polymorphs of hafnia predicted
within the framework of density functional theory. The full potential
linearised augmented plane wave method was employed together with the
Tran-Blaha modified Becke-Johnson potential for exchange and local density
approximation for correlation. Unit cells of monoclinic, cubic, and tetragonal
crystalline, and a simulated annealing-based model of amorphous hafnia were
fully relaxed with respect to internal positions and lattice parameters. The
thus obtained band gaps of 5.76 eV, 5.88 eV, 6.54 eV, and 5.5 eV for
monoclinic, cubic, tetragonal, and amorphous hafnia, respectively, are in
excellent agreement with available experimental data. Dielectric functions were
calculated and a shift of spectral weights to higher energies with respect to
experimental data was predicted. This was attributed to the random phase
approximation used to calculate the dielectric function, rather than
inaccuracies in the band structure.
