# web-page: bandstructure.png
"""Band structure tutorial

Calculate the band structure of Si along high symmetry directions
Brillouin zone
"""
# P1
from ase.build import bulk
from gpaw import GPAW, PW, FermiDirac

# Perform standard ground state calculation (with plane wave basis)
si = bulk('Si', 'diamond', 5.43)
calc = GPAW(mode=PW(200),
            xc='PBE',
            kpts=(8, 8, 8),
            random=True,  # random guess (needed if many empty bands required)
            occupations=FermiDirac(0.01),
            txt='Si_gs.txt')
si.calc = calc
si.get_potential_energy()
ef = calc.get_fermi_level()
calc.write('Si_gs.gpw')
# P2
# Restart from ground state and fix potential:
calc = GPAW('Si_gs.gpw').fixed_density(
    nbands=16,
    symmetry='off',
    kpts={'path': 'GXWKL', 'npoints': 60},
    convergence={'bands': 8})

# P3
bs = calc.band_structure()
bs.plot(filename='bandstructure.png', show=True, emax=10.0)