from ase.build import bulk
from gpaw import GPAW

si = bulk('Si', 'diamond', a=5.4)
si.calc = GPAW(mode='pw', kpts=(4, 4, 4))
si.get_potential_energy()

si.calc.set(fixdensity=True,
            kpts={'path': 'WLGXWK',
                  'npoints': 100},
            symmetry='off')
si.get_potential_energy()

bs = si.calc.band_structure()
bs.plot(emax=5.0, filename='bands.pdf')