Simplify System setup

[cortner]

The tutorial in ACEpotentials seems more complicated than necessary. The lines

data = FastSystem(ExtXYZ.Atoms(read_frame("initial structure in xyz file")))
atoms = [Molly.Atom( index=i, mass=AtomsBase.atomic_mass(data, i) ) for i in 1:length(data) ]
boundary = begin
    box = bounding_box(data)
    CubicBoundary(box[1][1], box[2][2], box[3][3])
end
atom_data = [ (; :Z=>z,:element=>s)  for (z,s) in zip(AtomsBase.atomic_number(data), AtomsBase.atomic_symbol(data))  ]

seem completely generic and could be wrapped into a convenience wrapper?

I'm not certain if that wrapper should be here or elsewhere though. This seems to have nothing to do with ACEmd or ACEpotentials? Maybe in AtomsBase?

[tjjarvinen]

This is to deal with Molly. So, Molly would also be the correct address for this.

I can do some fixing in ACEmd, but I need to make a PR in Molly to fix them properly.

[cortner]

then let's do it properly and go straight to Molly? Thanks for looking into it.