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import numpy as np
from ase import Atoms
from pytest import mark
@mark.calculator_lite
def test_multi_neighlist(KIM):
"""
To test that the correct energy/forces/stress can be computed using a
model that implements multiple cutoffs. This is done by construct a 10
Angstrom x 10 Angstrom x 10 Angstrom non-periodic cell filled with 15
randomly positioned atoms and requesting tha tthe model compute the
energy, forces, and virial stress. The energy returned by the model is
compared to a known precomputed value, while the forces and stress
returned are compared to numerical estimates via finite difference.
"""
# Create random cluster of atoms
positions = np.random.RandomState(34).rand(15, 3) * 10
atoms = Atoms(
"Ar" * 15, positions=positions, pbc=False, cell=[[10, 0, 0], [0, 10, 0], [0, 0, 10]]
)
calc = KIM("ex_model_Ar_P_Morse_MultiCutoff")
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 = 34.69963483186903 # 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)
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