def test_hex():
    """Test band structure from different variations of hexagonal cells."""
    import numpy as np
    from ase import Atoms
    from ase.calculators.test import FreeElectrons
    from ase.dft.kpoints import get_special_points

    firsttime = True
    for cell in [[[1, 0, 0], [0.5, 3**0.5 / 2, 0], [0, 0, 1]],
                 [[1, 0, 0], [-0.5, 3**0.5 / 2, 0], [0, 0, 1]],
                 [[0.5, -3**0.5 / 2, 0], [0.5, 3**0.5 / 2, 0], [0, 0, 1]]]:
        a = Atoms(cell=cell, pbc=True)
        a.cell *= 3
        a.calc = FreeElectrons(nvalence=1, kpts={'path': 'GMKG'})
        lat = a.cell.get_bravais_lattice()
        assert lat.name == 'HEX'
        print(repr(a.cell.get_bravais_lattice()))
        #print(crystal_structure_from_cell(a.cell))
        r = a.cell.reciprocal()
        k = get_special_points(a.cell)['K']
        print(np.dot(k, r))
        a.get_potential_energy()
        bs = a.calc.band_structure()
        coords, labelcoords, labels = bs.get_labels()
        assert ''.join(labels) == 'GMKG'
        e_skn = bs.energies
        if firsttime:
            coords1 = coords
            labelcoords1 = labelcoords
            e_skn1 = e_skn
            firsttime = False
        else:
            for d in [coords - coords1,
                      labelcoords - labelcoords1,
                      e_skn - e_skn1]:
                assert abs(d).max() < 1e-13
        # bs.plot()