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"""Tests for `FiniteDifferenceCalculator`."""
import numpy as np
import pytest
from ase import Atoms
from ase.build import bulk
from ase.calculators.emt import EMT
from ase.calculators.fd import FiniteDifferenceCalculator
@pytest.fixture(name='atoms')
def fixture_atoms() -> Atoms:
"""Make a fixture of atoms."""
atoms = bulk('Cu', cubic=True)
atoms.rattle(0.1)
return atoms
def test_fd(atoms: Atoms) -> None:
"""Test `FiniteDifferenceCalculator`."""
atoms.calc = EMT()
energy_analytical = atoms.get_potential_energy()
forces_analytical = atoms.get_forces()
stress_analytical = atoms.get_stress()
atoms.calc = FiniteDifferenceCalculator(EMT())
energy_numerical = atoms.get_potential_energy()
forces_numerical = atoms.get_forces()
stress_numerical = atoms.get_stress()
# check if `numerical` energy is exactly equal to `analytical`
assert energy_numerical == energy_analytical
# check if `numerical` forces are *not* exactly equal to `analytical`
assert np.any(forces_numerical != forces_analytical)
assert np.any(stress_numerical != stress_analytical)
np.testing.assert_allclose(forces_numerical, forces_analytical)
np.testing.assert_allclose(stress_numerical, stress_analytical)
def test_analytical_forces(atoms: Atoms) -> None:
"""Test if analytical forces are available."""
atoms.calc = EMT()
forces_ref = atoms.get_forces()
atoms.calc = FiniteDifferenceCalculator(EMT(), eps_disp=None)
forces_fdc = atoms.get_forces()
# check if forces are *exactly* equal to `analytical`
np.testing.assert_array_equal(forces_fdc, forces_ref)
def test_analytical_stress(atoms: Atoms) -> None:
"""Test if analytical stress is available."""
atoms.calc = EMT()
stress_ref = atoms.get_stress()
atoms.calc = FiniteDifferenceCalculator(EMT(), eps_strain=None)
stress_fdc = atoms.get_stress()
# check if stress is *exactly* equal to `analytical`
np.testing.assert_array_equal(stress_fdc, stress_ref)
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