Corundum Al2O3. Forces were calculated in the 2x2x1 supercell of the hexagonal lattice by VASP with 500eV cutoff energy and 6x6x1 k-point mesh.

Dielectric constant and Born effective charge tensors were calculated with the hexagonal unit cell.

The Wyckoff positions are c and e, respectively, which can be found by

% phonopy -c POSCAR-unitcell --symmetry --pa=auto

The band structure is plotted using seekpath by

% phonopy --nac --band auto -p

seekpath can be installed by "pip install seekpath".
