PwBandsWorkChain: Move inputs to protocol

Several "default" inputs of the `PwBandsWorkChain` are set inside one of the steps of the work chain, which:

1. Can be confusing for the user, since the expected inputs are not there in the input files.
2. Can be frustrating for the user when a different value is desirable, for a use case that may not immediately be obvious.
3. Means default values are specified _both_ in the work chain logic and protocol, making it more difficult to get a clear overview of the input parameters.

Here we move the specification of the default inputs to the protocol file of the `PwBandsWorkChain` (`bands.yaml`). We also explicitly set the restart inputs to make sure the `bands` calculations restarts from the charge density by default.

Since the default protocol now correctly sets the calculation type to `bands`, the `validate_inputs` validator of the `PwCalculation` will raise a warning because a `parent_folder` has not been initially provided. Hence, we set the `validate_inputs_base` validator for the `pw` port of the `bands` namespace, as is also done for e.g. the `nscf` of the `PdosWorkchain`.

src/aiida_quantumespresso/workflows/protocols/pw/bands.yaml

@@ -2,6 +2,21 @@ default_inputs:
     bands_kpoints_distance: 0.025
     clean_workdir: True
     nbands_factor: 3.0
+    scf:
+        pw:
+            parameters:
+                CONTROL:
+                    calculation: scf
+    bands:
+        pw:
+            parameters:
+                CONTROL:
+                    calculation: bands
+                    restart_mode: from_scratch
+                ELECTRONS:
+                    diagonalization: paro
+                    diago_full_acc: True
+                    startingpot: file
 default_protocol: moderate
 protocols:
     moderate:

src/aiida_quantumespresso/workflows/pw/bands.py

@@ -3,16 +3,15 @@
 from aiida import orm
 from aiida.common import AttributeDict
 from aiida.engine import ToContext, WorkChain, if_
-from aiida.plugins import WorkflowFactory
 
 from aiida_quantumespresso.calculations.functions.seekpath_structure_analysis import seekpath_structure_analysis
+from aiida_quantumespresso.calculations.pw import PwCalculation
 from aiida_quantumespresso.utils.mapping import prepare_process_inputs
+from aiida_quantumespresso.workflows.pw.base import PwBaseWorkChain
+from aiida_quantumespresso.workflows.pw.relax import PwRelaxWorkChain
 
 from ..protocols.utils import ProtocolMixin
 
-PwBaseWorkChain = WorkflowFactory('quantumespresso.pw.base')
-PwRelaxWorkChain = WorkflowFactory('quantumespresso.pw.relax')
-
 
 def validate_inputs(inputs, ctx=None):  # pylint: disable=unused-argument
     """Validate the inputs of the entire input namespace."""
@@ -72,6 +71,7 @@ def define(cls, spec):
             help='Explicit kpoints to use for the BANDS calculation. Specify either this or `bands_kpoints_distance`.')
         spec.input('bands_kpoints_distance', valid_type=orm.Float, required=False,
             help='Minimum kpoints distance for the BANDS calculation. Specify either this or `bands_kpoints`.')
+        spec.inputs['bands']['pw'].validator = PwCalculation.validate_inputs_base
         spec.inputs.validator = validate_inputs
         spec.outline(
             cls.setup,
@@ -229,7 +229,6 @@ def run_scf(self):
         inputs.metadata.call_link_label = 'scf'
         inputs.pw.structure = self.ctx.current_structure
         inputs.pw.parameters = inputs.pw.parameters.get_dict()
-        inputs.pw.parameters.setdefault('CONTROL', {})['calculation'] = 'scf'
 
         # Make sure to carry the number of bands from the relax workchain if it was run and it wasn't explicitly defined
         # in the inputs. One of the base workchains in the relax workchain may have changed the number automatically in
@@ -267,13 +266,6 @@ def run_bands(self):
         inputs.pw.parameters.setdefault('SYSTEM', {})
         inputs.pw.parameters.setdefault('ELECTRONS', {})
 
-        # The following flags always have to be set in the parameters, regardless of what caller specified in the inputs
-        inputs.pw.parameters['CONTROL']['calculation'] = 'bands'
-
-        # Only set the following parameters if not directly explicitly defined in the inputs
-        inputs.pw.parameters['ELECTRONS'].setdefault('diagonalization', 'cg')
-        inputs.pw.parameters['ELECTRONS'].setdefault('diago_full_acc', True)
-
         # If `nbands_factor` is defined in the inputs we set the `nbnd` parameter
         if 'nbands_factor' in self.inputs:
             factor = self.inputs.nbands_factor.value

tests/workflows/protocols/pw/test_bands.py

@@ -87,7 +87,7 @@ def test_options(fixture_code, generate_structure):
 
     for subspace in (
         builder.relax.base.pw.metadata,
-        builder.scf.pw.metadata,
-        builder.bands.pw.metadata,
+        builder.scf.pw.metadata,  # pylint: disable=no-member
+        builder.bands.pw.metadata,  # pylint: disable=no-member
     ):
         assert subspace['options']['queue_name'] == queue_name, subspace

tests/workflows/protocols/pw/test_bands/test_default.yml

@@ -9,13 +9,15 @@ bands:
         withmpi: true
     parameters:
       CONTROL:
-        calculation: scf
+        calculation: bands
         etot_conv_thr: 2.0e-05
         forc_conv_thr: 0.0001
         tprnfor: true
         tstress: true
       ELECTRONS:
         conv_thr: 4.0e-10
+        diago_full_acc: true
+        diagonalization: paro
         electron_maxstep: 80
         mixing_beta: 0.4
       SYSTEM: