from gpaw import GPAW
from ase.data.molecules import molecule
from gpaw.utilities import h2gpts
from gpaw.poisson import PoissonSolver
from gpaw.dipole_correction import DipoleCorrectionPoissonSolver

system = molecule('H2O')
system.center(vacuum=3.0)
system.center(vacuum=6.0, axis=2)

ps = PoissonSolver(relax='GS', eps=1e-9)
dcps = DipoleCorrectionPoissonSolver(ps, 2) # 2 refers to the z axis

calc = GPAW(mode='lcao',
            basis='dzp',
            poissonsolver=dcps)

system.set_calculator(calc)
system.get_potential_energy()