def test_cgf_repulsion(self):
"""
Test two-electron integrals for contracted Gaussians
(ij|kl) = <cgf_i cgf_j | r_ij | cgf_k cgf_l>
"""
# construct integrator object
integrator = PyQInt()
# build hydrogen molecule
mol = Molecule("H2")
mol.add_atom('H', 0.0, 0.0, 0.0)
mol.add_atom('H', 0.0, 0.0, 1.4)
cgfs, nuclei = mol.build_basis('sto3g')
T1111 = integrator.repulsion(cgfs[0], cgfs[0], cgfs[0], cgfs[0])
T1122 = integrator.repulsion(cgfs[0], cgfs[0], cgfs[1], cgfs[1])
T1112 = integrator.repulsion(cgfs[0], cgfs[0], cgfs[0], cgfs[1])
T2121 = integrator.repulsion(cgfs[1], cgfs[0], cgfs[1], cgfs[0])
T1222 = integrator.repulsion(cgfs[0], cgfs[1], cgfs[1], cgfs[1])
T2211 = integrator.repulsion(cgfs[1], cgfs[1], cgfs[0], cgfs[0])
np.testing.assert_almost_equal(T1111, 0.7746056914329529, 4)
np.testing.assert_almost_equal(T1122, 0.5696758031845093, 4)
np.testing.assert_almost_equal(T1112, 0.4441076656879812, 4)
np.testing.assert_almost_equal(T2121, 0.2970285713672638, 4)
# test similarity between two-electron integrals
np.testing.assert_almost_equal(T1222, T1112, 4)
np.testing.assert_almost_equal(T1122, T2211, 4)
def calculate_force_finite_difference(mol, nuc_id, cgf_id1, cgf_id2, cgf_id3,
cgf_id4, coord):
# build integrator object
integrator = PyQInt()
# distance
diff = 0.00001
mol1 = deepcopy(mol)
mol1.atoms[nuc_id][1][coord] -= diff / 2
mol2 = deepcopy(mol)
mol2.atoms[nuc_id][1][coord] += diff / 2
# build hydrogen molecule
cgfs1, nuclei = mol1.build_basis('sto3g')
left = integrator.repulsion(cgfs1[cgf_id1], cgfs1[cgf_id2], cgfs1[cgf_id3],
cgfs1[cgf_id4])
cgfs2, nuclei = mol2.build_basis('sto3g')
right = integrator.repulsion(cgfs2[cgf_id1], cgfs2[cgf_id2],
cgfs2[cgf_id3], cgfs2[cgf_id4])
return (right - left) / diff
