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import numpy as np
from pytest import mark
from ase.lattice.cubic import FaceCenteredCubic
@mark.calculator_lite
def test_energy_forces_stress(KIM):
"""
To test that the calculator can produce correct energy and forces. This
is done by comparing the energy for an FCC argon lattice with an example
model to the known value; the forces/stress returned by the model are
compared to numerical estimates via finite difference.
"""
# Create an FCC atoms crystal
atoms = FaceCenteredCubic(
directions=[[1, 0, 0], [0, 1, 0], [0, 0, 1]],
size=(1, 1, 1),
symbol="Ar",
pbc=(1, 0, 0),
latticeconstant=3.0,
)
# Perturb the x coordinate of the first atom by less than the cutoff distance
atoms.positions[0, 0] += 0.01
calc = KIM("ex_model_Ar_P_Morse_07C")
atoms.calc = calc
# Get energy and analytical forces/stress from KIM model
energy = atoms.get_potential_energy()
forces = atoms.get_forces()
stress = atoms.get_stress()
# Previously computed energy for this configuration for this model
energy_ref = 19.7196709065 # eV
# Compute forces and virial stress numerically
forces_numer = calc.calculate_numerical_forces(atoms, d=0.0001)
stress_numer = calc.calculate_numerical_stress(atoms, d=0.0001, voigt=True)
tol = 1e-6
assert np.isclose(energy, energy_ref, tol)
assert np.allclose(forces, forces_numer, tol)
assert np.allclose(stress, stress_numer, tol)
# This has been known to segfault
atoms.set_pbc(True)
atoms.get_potential_energy()
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