Update documentation

docs/source/user_guide/command_line.rst

@@ -314,7 +314,7 @@ Calculate phonons with a 2x2x2 supercell, after geometry optimization (using the
 
 .. code-block:: bash
 
-    janus phonons --struct tests/data/NaCl.cif --supercell 2 2 2 --minimize --arch mace_mp --model-path small
+    janus phonons --struct tests/data/NaCl.cif --supercell "2 2 2" --minimize --arch mace_mp --model-path small
 
 
 This will save the Phonopy parameters, including displacements and force constants, to ``NaCl-phonopy.yml`` and ``NaCl-force_constants.hdf5``,
@@ -324,7 +324,7 @@ Additionally, the ``--bands`` option can be added to calculate the band structur
 
 .. code-block:: bash
 
-    janus phonons --struct tests/data/NaCl.cif --supercell 2 2 2 --minimize --arch mace_mp --model-path small --bands
+    janus phonons --struct tests/data/NaCl.cif --supercell "2 2 2" --minimize --arch mace_mp --model-path small --bands
 
 
 If you need eigenvectors and group velocities written, add the ``--write-full`` option. This will generate a much larger file, but can be used to visualise phonon modes.
@@ -333,7 +333,7 @@ Further calculations, including thermal properties, DOS, and PDOS, can also be c
 
 .. code-block:: bash
 
-    janus phonons --struct tests/data/NaCl.cif --supercell 2 3 4 --dos --pdos --thermal --temp-start 0 --temp-end 300 --temp-step 50
+    janus phonons --struct tests/data/NaCl.cif --supercell "2 3 4" --dos --pdos --thermal --temp-start 0 --temp-end 300 --temp-step 50
 
 
 This will create additional output files: ``NaCl-thermal.dat`` for the thermal properties (heat capacity, entropy, and free energy)

janus_core/cli/phonons.py

@@ -237,10 +237,8 @@ def phonons(
         supercell = supercell[0]
     elif supercell_length not in [3, 9]:
         raise ValueError(
-            "Please pass one, three or nine lattice vectors in the form '1', '1 2 3' "
-            "or '1 2 3 4 5 6 7 8 9'. In the latter case first three values are the "
-            "first row of the supercell matrix, the second three are the second row, "
-            "etc."
+            "Please pass lattice vectors as space-separated integers in quotes. "
+            "For example, '1 2 3'."
         )
 
     calcs = []