add test for molecule with xyzfile

doc/source/getting-started/hamiltonian.rst

@@ -2,9 +2,9 @@
 Hamiltonian
 ===========
 
-Central to quantum chemical calculations for molecules is the fermionic two-body Hamiltonian in second quantized form.
+Central to quantum chemical calculations for molecules is the fermionic spin-free nonrelativistic two-body Hamiltonian in second quantized form in the absence of external fields.
 
-TODO: spinfree, nonrelativistic, without external fields, without nuclear-repulsion energy
+In most literature it is written as follows, neglecting terms for the nuclear repulsion energy which is a constant under the Born-Oppenheimer approximation:
 
 .. math::
     \hat{H} = \sum_{pq} h_{pq} a^\dagger_p a_q + \frac12 \sum_{pqrs} g_{pqrs} a^\dagger_p a^\dagger_r a_s a_q

tests/lih.xyz

@@ -0,0 +1,4 @@
+2
+0 1
+Li 0.0 0.0 0.0
+H 0.0 0.0 1.2

tests/test_molecule.py

@@ -22,6 +22,16 @@ def test_run_pyscf():
     assert h2.e_hf == pytest.approx(h2_ref_energy)
     assert np.allclose(h2.hcore, h2_ref_hcore)
 
+def test_run_pyscf_molecule_xyz():
+    """Pyscf driver with xyz file"""
+
+    lih_ref_energy =  -7.83561582555692
+    lih = Molecule(xyz_file="lih.xyz")
+    lih.run_pyscf()
+
+    assert lih.e_hf == pytest.approx(lih_ref_energy)
+
+
 
 @pytest.mark.skip(reason="psi4 doesn't offer pip install, so needs to be installed through conda or manually.")
 def test_run_psi4():