Species handling struggles with _

[PythonFZ]

Describe the bug
This is just one example

MDSuite/mdsuite/calculators/radial_distribution_function.py

Line 313 in 6ed32d4

species_split = species.split("_")

that failes if the species contain _ e.g. Na_1

also a bit related to #486

[SamTov]

That can certainly happen in some simulations. There is a possible approach to this I would like to discuss at the general meeting.

[PythonFZ]

That can certainly happen in some simulations. There is a possible approach to this I would like to discuss at the general meeting.

If you have a good idea can you briefly describe it here?

[christophlohrmann]

is there a way to keep it internally as tuple(str) and just convert it to the underscore-string when returning it to the user?

tuple means it is fixed order and can be used as a dict key if needed