from ase.build import molecule
from gpaw import GPAW

a = 8.0

energies = {}
for ecut in [300, 400, 500]:
    with open(f'results-{ecut:3.0f}.txt', 'w') as resultfile:

        for name in ['H2O', 'H', 'O']:
            atoms = molecule(name)
            atoms.set_cell((a, a, a))
            atoms.center()

            if name in ['H', 'O']:
                hund = True
            else:
                hund = False

            calc = GPAW(mode={'name': 'pw', 'ecut': ecut}, hund=hund,
                        txt=f'gpaw-{name}-{ecut:3.0f}.txt')
            atoms.calc = calc

            energy = atoms.get_potential_energy()
            energies[name] = energy
            print(name, energy, file=resultfile)

        e_atomization = energies['H2O'] - 2 * energies['H'] - energies['O']
        print(e_atomization, file=resultfile)