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import pytest
import numpy as np
from ase.build import molecule
from ase.md.velocitydistribution import Stationary, ZeroRotation
norm = np.linalg.norm
@pytest.fixture
def atoms():
rng = np.random.RandomState(0)
atoms = molecule('CH3CH2OH')
momenta = -0.5 + rng.rand(len(atoms), 3)
atoms.set_momenta(momenta)
return atoms
@pytest.fixture
def stationary_atoms(atoms):
atoms = atoms.copy()
Stationary(atoms)
return atoms
def propagate(atoms):
dt = 0.1
atoms = atoms.copy()
velocities = atoms.get_velocities()
displacement = velocities * dt
atoms.positions += displacement
return atoms
def test_stationary(atoms, stationary_atoms):
assert norm(atoms.get_momenta().sum(axis=0)) > 0.1
assert norm(stationary_atoms.get_momenta().sum(axis=0)) < 1e-13
def test_stationary_propagate(atoms, stationary_atoms):
# Test that center of mass is stationary by time propagation
prop_atoms = propagate(atoms)
stationary_prop_atoms = propagate(stationary_atoms)
com = atoms.get_center_of_mass()
# Center of mass have moved (a bit, at least):
assert norm(prop_atoms.get_center_of_mass() - com) > 1e-4
assert norm(stationary_prop_atoms.get_center_of_mass() - com) < 1e-13
def test_zero_rotation(atoms):
mom1 = atoms.get_angular_momentum()
ZeroRotation(atoms)
mom2 = atoms.get_angular_momentum()
assert norm(mom1) > 0.1
assert norm(mom2) < 1e-13
# Can we write a "propagation" test for zero rotation as well?
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