Nexus: expand eshdf features

[Paul-St-Young]

Proposed changes

No change to default behavior. Options added:

1. --fnk3d outputs the 3D n(k) to the specified hdf file
2. --ispin=0,1 targets spin channel
3. --ncore and --nval define ``active'' orbitals that contribute to n(k)

What type(s) of changes does this code introduce?

• New feature

Does this introduce a breaking change?

• No

What systems has this change been tested on?

workstation, Xeon 6234, CentOS 7

Checklist

Update the following with a yes where the items apply. If you're unsure about any of them, don't hesitate to ask. This is
simply a reminder of what we are going to look for before merging your code.

• Yes. This PR is up to date with current the current state of 'develop'
• No. Code added or changed in the PR has been clang-formatted
• No. This PR adds tests to cover any new code, or to catch a bug that is being fixed
• No. Documentation has been added (if appropriate)

[qmc-robot]

Can one of the admins verify this patch?

[jtkrogel]

The functionality here looks good. The intended usage of eshdf is eshdf [mode] [options]. Please can you move the new functionality to a new function at the same level as kinetic (e.g. write_nk) that will process only what is needed for n(k) according to the new options you introduce? Invocation would then look like e.g. eshdf write_nk [options].

[Paul-St-Young]

@jtkrogel I split out the write_nk subcommand like you suggested.
I also pulled out two option parsing subroutines from kinetic() to reuse in write_nk()

1. first_eshdf_file
2. interpret_nk_options

Please see if this PR is now satisfactory.

[jtkrogel]

@Paul-St-Young This looks OK now. Please can you just quickly confirm that running eshdf kinetic ... produces the same output as before?

[Paul-St-Young]

@jtkrogel yes, I can confirm eshdf kinetic works the same as before on my example wf h5 file.

[jtkrogel]

LGTM

[ye-luo]

Test this please