Set relax type none and no properites to run SCF only

[unkcpz]

fixes #264

Using RelaxType.NONE for relax workchain to run the SCF only.
The builder is constructed with all three workchain input parameters port, relax, bands, pdos.
Whether to run sub-workchain is controlled by popping the input key out from the builder, right after the builder is created.
Also, the relax/properties infos of workchain selector is changed to show this newly add calculation type as 'SCF only'.

[superstar54]

One comment, after the SCF calculation, what results could the user get? Currently, the energy and force are not printed out in the result section. Better to implement this also. Otherwise, the calculation is meaningless.

[superstar54]

It is also confusing that one runs a SCF calculation using the relax port. Better to add a SCF workchain, to make the code clean and readable.

[unkcpz]

Thanks! @superstar54

after the SCF calculation, what results could the user get? Currently, the energy and force are not printed out in the result section. Better to implement this also. Otherwise, the calculation is meaningless.

This is a very good point. But this issue came from the in-person testing with Nicola that when selecting not relax and no properties are chosen the qeApp will block the calculation from running by throwing a warning.
Is that possible to leave it in the future since we do not decide yet what to show as the output of the SCF only calculation? I'll open an issue for it.

It is also confusing that one runs a SCF calculation using the relax port. Better to add a SCF workchain, to make the code clean and readable.

I also had same feeling when start working on this. But qeApp is simply the UI wrapper of aiida-quantumespresso, I think the change should be make there. @mbercx can you comment on if you think this is worth implementing?
I think we can basically add an alias workchain called PwScfOnlyWorkChain sort of, and have it point to Relax with the parameters fixed. The question is where to put this workchain? If it is not a case to add in aiida-quantumespresso, I think it is also make sense to have the workchain here in QeApp/src. I'll add it in this PR.

[unkcpz]

Hi @superstar54, I change the message show in workflow bar. But I still not add the energies showed in the output tabs. Since I don't decide yet where to add it, it can be on in the Workflow summary or as a new tab with all related and necessary output parameters. I open an issue at #311.
Let's focus on it with another PR.

[mbercx]

Re the SCF only output: I think one of the possible outputs Nicola had in mind would be the charge density. However, I don't think it's possible to extract the charge density file atm. I'll add that originally we blocked this type of calculation for this very reason: I saw little point in running only an SCF for a layman user. The total energy of a single calculation is also not super meaningful, I'd say? The forces could be useful in some cases, I suppose.

Re the relax work chain: An "SCF" work chain would simply be the PwBaseWorkChain, no? The RelaxType.NONE implementation comes from the common workflows project, there it was decided to add this relax type for technical reasons, and here we simply repurpose this to make the implementation somewhat easier. I'd have to take a closer look at the code (which I'll try to make some time for ASAP, many apologies @unkcpz!), but I think you'd also have to make quite some significant changes to the QeAppWorkChain to add this to a proper (optional) port. Not sure if the resulting code would be easier to maintain.

[unkcpz]

@mbercx Thanks! I update the #311 with your comment. I think for the current one, it is okay to use the PwRelaxWorkChain with RelaxType.None. Since in my opinion, we should not add complexity to the workchain of QeApp but just light wrapper of what already implement in the aiida-quantumespresso.

@superstar54 could you have another look and let's try get this PR done?

[superstar54]

Why is "none", not None or "None". Please make sure "none" is correct.

If it is correct, we need to change it to a more standard way, e.g. None

[unkcpz]

relax_type is a parameter read from widget.

        # RelaxType: degrees of freedom in geometry optimization
        self.relax_type = ipw.ToggleButtons(
            options=[
                ("Structure as is", "none"),
                ("Atomic positions", "positions"),
                ("Full geometry", "positions_cell"),
            ],
            value="positions_cell",
        )

The string type is used to distinguish the None in purpose.

[superstar54]

I think this try ... except is not used, because it will always run a relax (scf or real relax) calculation.

[superstar54]

Could you explain the difference between relax (only scf) and relax sub-workflow? I am not very clear about this, thanks.

[unkcpz]

You can find how this tag change the parameters set in pw.x input file at https://github.com/aiidateam/aiida-quantumespresso/blob/d15f8cd1032e37ae59a19d733ee5ae1ed59e1f10/src/aiida_quantumespresso/workflows/pw/relax.py#L123-L146

[superstar54]

LGTM