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from numpy.testing import assert_allclose
import ase.build
from ase.calculators.emt import EMT
def test_potential_energies():
TOL = 1E-8
atoms = ase.build.bulk("Ni", crystalstructure="fcc", cubic=1)
atoms *= (2, 2, 2)
atoms.calc = EMT()
energies = atoms.get_potential_energies()
energy = atoms.get_potential_energy()
# energy sums should be identical
assert abs(energies.sum() - energy) < TOL
# in ideal FCC crystal per-atom energies should be identical
assert_allclose(energies, energies[0], rtol=TOL)
# rattle the system and check energy sums again
atoms.rattle()
assert abs(energies.sum() - energy) < TOL
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