xtbout.json not written for GFN-FF

[nielskm]

The xtbout.json file that should be written when passing the --json flag is not generated when running GFN-FF calculations.

To Reproduce
Running xtb <some-molecule.xyz> --gfnff --json produces no JSON output file.

Additional context
xtb version: 6.5.1

[MtoLStoN]

The "--json" flag is, at the moment, not used in conjunction with GFN-FF. We could use this flag to write all available information (replacing the need to use the --wrtopo flag with keywords). See #750.
Is that what you had in mind?

[nielskm]

@MtoLStoN Thank you for taking the time to look at this. I was simply thinking if you could output a JSON containing total energy, etc. as done for the xTB methods.

[MtoLStoN]

I understand; I'll look into this. This should be relatively easy to do, if I find the time. If this is something you want faster, you are more than welcome to submit a patch.

The relevant call can be found here:

xtb/src/prog/main.F90

Lines 860 to 868 in 863dcdc

	if (set%pr_json) then
	select type(calc)
	type is(TxTBCalculator)
	call open_file(ich,'xtbout.json','w')
	call main_json(ich, &
	mol,chk%wfn,calc%basis,res,fres)
	call close_file(ich)
	end select
	endif

And we would need an additional writer routine for the GFN-FF json file.

https://github.com/grimme-lab/xtb/blob/main/src/main/json.f90

This could probably be done with an explicit interface and a second writer routine just for GFN-FF.

[MtoLStoN]

Thanks to @Thomas3R, we have this implemented now!