Fix for a bug inside of christiansen_integrals_dipole

pennylane/labs/tests/vibrational/test_christiansen_ham.py

@@ -150,6 +150,13 @@ def test_christiansen_integrals_dipole():
     assert np.allclose(abs(two), abs(D2), atol=1e-8)
     assert np.allclose(abs(three), abs(D3), atol=1e-8)
 
+def test_christiansen_integrals_dipole_conditional():
+    """Test that christiansen_integrals_dipole works even when there is only two mode dipoles."""
+    coeffs = christiansen_integrals_dipole(pes=pes_object_2D, n_states=4)
+    assert np.allclose(abs(coeffs[0]), abs(D1), atol=1e-8)
+    assert np.allclose(abs(coeffs[1]), abs(D2), atol=1e-8)
+    assert len(coeffs) == 2
+
 
 def test_cform_onemode():
     """Test that _cform_onemode produces the expected one-body integral."""

pennylane/labs/vibrational/christiansen_utils.py

@@ -848,7 +848,7 @@ def christiansen_integrals_dipole(pes, n_states=16):
     comm.Barrier()
     dipole_cform_onebody = comm.bcast(dipole_cform_onebody, root=0)
 
-    if pes.localized is True or pes.dipole_level > 1:
+    if pes.dipole_level > 1:
         local_dipole_cform_twobody = _cform_twomode_dipole(pes, n_states)
         comm.Barrier()
 
@@ -865,7 +865,7 @@ def christiansen_integrals_dipole(pes, n_states=16):
         comm.Barrier()
         dipole_cform_twobody = comm.bcast(dipole_cform_twobody, root=0)
 
-    if pes.localized is True or pes.dipole_level > 2:
+    if pes.dipole_level > 2:
         local_dipole_cform_threebody = _cform_threemode_dipole(pes, n_states)
         comm.Barrier()