Add test for TwoCenterIntegrator for pyabacus.

Author: ErjieWu

python/pyabacus/tests/test_m_nao.py

@@ -73,7 +73,36 @@ def test_rc():
     assert orb(0,1,1).l == 1
     assert orb(0,2,0).l == 2
 
+def test_twocenterintegrator():
+    orb_dir = '../../../tests/PP_ORB/'
+    file_list = ["C_gga_8au_100Ry_2s2p1d.orb", "O_gga_10au_100Ry_2s2p1d.orb"]
+    file_list = [orb_dir + orbfile for orbfile in file_list]
+
+    orb = nao.RadialCollection()
+    orb.build(2, file_list, 'o')
+
+    alpha = nao.RadialCollection()
+    alpha.build(1, [file_list[0]])
+
+    dr = 0.01  # R spacing
+    rmax = max(orb.rcut_max, alpha.rcut_max)
+    cutoff = 2.0 * rmax
+    nr = int(rmax / dr) + 1
+
+    orb.set_uniform_grid(True, nr, cutoff, 'i', True)
+    alpha.set_uniform_grid(True, nr, cutoff, 'i', True)
+
+    sbt = base.SphericalBesselTransformer()
+    orb.set_transformer(sbt)
+    alpha.set_transformer(sbt)
+
+    integrator = nao.TwoCenterIntegrator()
+    integrator.tabulate(orb, alpha, 'S', nr, cutoff)
 
+    overlap = integrator.snap(0, 0, 0, 0, 0, np.array([0.0, 0.0, 0.0]), False)
+    assert 1 - overlap[0][0] < 1e-10
+    overlap = integrator.snap(1, 0, 0, 0, 0, np.array([3.0, 3.0, 3.0]), False)
+    assert abs(overlap[0][0] - 0.031136758774787342) < 1e-10