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add elc test on madelung energy #4785

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Dec 8, 2023
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add elc test on madelung energy #4785

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56 changes: 51 additions & 5 deletions testsuite/python/elc.py
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
#
# Copyright (C) 2010-2022 The ESPResSo project
# Copyright (C) 2010-2023 The ESPResSo project
#
# This file is part of ESPResSo.
#
Expand All @@ -22,15 +22,13 @@
import espressomd.electrostatics

import numpy as np
import itertools

GAP = np.array([0., 0., 3.])
BOX_L = np.array(3 * [10.]) + GAP
TIME_STEP = 1e-100
POTENTIAL_DIFFERENCE = -3.


class ElcTest:
system = espressomd.System(box_l=BOX_L, time_step=TIME_STEP)
system = espressomd.System(box_l=[1.] * 3, time_step=TIME_STEP)
system.cell_system.skin = 0.0

def tearDown(self):
Expand All @@ -40,6 +38,12 @@ def tearDown(self):
def test_finite_potential_drop(self):
system = self.system

GAP = np.array([0., 0., 3.])
BOX_L = np.array(3 * [10.]) + GAP
POTENTIAL_DIFFERENCE = -3.

system.box_l = BOX_L

p1 = system.part.add(pos=[0, 0, 1], q=+1)
p2 = system.part.add(pos=[0, 0, 9], q=-1)

Expand Down Expand Up @@ -90,6 +94,48 @@ def test_finite_potential_drop(self):
with self.assertRaisesRegex(Exception, 'entered ELC gap region'):
self.system.integrator.run(2)

def test_elc_p3m_madelung(self):
system = self.system

n_pairs = 6

BOX_L = 2 * n_pairs
ELC_GAP = 0.4 * BOX_L
system.box_l = [BOX_L, BOX_L, BOX_L + ELC_GAP]

for j, k, l in itertools.product(range(2 * n_pairs), repeat=3):
system.part.add(pos=[j + 0.5, k + 0.5, l + 0.5],
q=(-1)**(j + k + l))

p3m = self.p3m_class(
prefactor=1,
mesh=[60, 60, 84],
cao=7,
r_cut=3.314,
alpha=1.18,
accuracy=3e-7,
tune=False,
)
elc = espressomd.electrostatics.ELC(
actor=p3m,
gap_size=ELC_GAP,
maxPWerror=3e-7,
delta_mid_top=-1,
delta_mid_bot=-1,
const_pot=True,
pot_diff=0,
)

system.electrostatics.solver = elc

MADELUNG = -1.74756459463318219
U_expected = MADELUNG

U_elc = 2. * \
system.analysis.energy()['coulomb'] / len(system.part.all())

np.testing.assert_allclose(U_elc, U_expected, atol=0., rtol=1e-6)


@utx.skipIfMissingFeatures(["P3M"])
class ElcTestCPU(ElcTest, ut.TestCase):
Expand Down