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# fmt: off
import numpy as np
from ase import Atoms, units
from ase.calculators.counterions import AtomicCounterIon as ACI
from ase.calculators.fd import calculate_numerical_forces
def test_counterions():
""" Test AtomicCounterIon is force/energy consistent over
PBCs and with cutoff """
sigma = 1.868 * (1.0 / 2.0)**(1.0 / 6.0)
epsilon = 0.00277 * units.kcal / units.mol
atoms = Atoms('3Na', positions=np.array([[0, 0, -2], [0, 0, 0], [0, 0, 2]]))
atoms.cell = [10, 10, 10]
atoms.pbc = True
atoms.calc = ACI(1, epsilon, sigma, rc=4.5)
points = np.arange(-15., 15., 0.2)
for _ in points:
f = atoms.get_forces()
fn = calculate_numerical_forces(atoms, 1e-5)
df = (f - fn)
assert abs(df).max() < 1e-8
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