def test_coulomb(self):
coulomb_k = 1
q1 = 1
q2 = -1
self.system.part[0].q = q1
self.system.part[1].q = q2
self.run_test(
espressomd.interactions.BondedCoulomb(prefactor=coulomb_k),
lambda r: tests_common.coulomb_force(r, coulomb_k, q1, q2),
lambda r: tests_common.coulomb_potential(r, coulomb_k, q1, q2),
0.01, self.system.box_l[0] / 3)
def test_coulomb(self):
coulomb_k = 1
q1 = 1
q2 = -1
self.system.part[0].q = q1
self.system.part[1].q = q2
coulomb = espressomd.interactions.BondedCoulomb(prefactor=coulomb_k)
self.system.bonded_inter.add(coulomb)
self.system.part[0].add_bond((coulomb, 1))
for i in range(445):
self.system.part[1].pos = self.system.part[1].pos + self.step
self.system.integrator.run(recalc_forces=True, steps=0)
# Calculate energies
E_sim = self.system.analysis.energy()["bonded"]
E_ref = tests_common.coulomb_potential(scalar_r=(i + 1) *
self.step_width,
k=coulomb_k,
q1=q1,
q2=q2)
# Calculate forces
f0_sim = self.system.part[0].f
f1_sim = self.system.part[1].f
f1_ref = self.axis * tests_common.coulomb_force(
scalar_r=(i + 1) * self.step_width, k=coulomb_k, q1=q1, q2=q2)
# Check that energies match, ...
np.testing.assert_almost_equal(E_sim, E_ref)
# force equals minus the counter-force ...
self.assertTrue((f0_sim == -f1_sim).all())
# and has correct value.
f1_sim_copy = np.copy(f1_sim)
np.testing.assert_almost_equal(f1_sim_copy, f1_ref)