Make OpenBabel read pymatgen format

[correaa]

Is your feature request related to a problem? Please describe.

The new Materials Project API (https://next-gen.materialsproject.org/api) seems to only report structures in the pymatgen format only.

For example a REST request of this type "https://api.materialsproject.org/materials/summary/?material_ids=mp-66&_fields=structure",headers={"X-API-KEY": MP_API_KEY}" returns

{"data":[{"structure":{"@module":"pymatgen.core.structure","@class":"Structure","charge":0,"lattice":{"matrix":[[2.18050236,0.0,1.25891346],[0.72683412,2.05579703,1.25891346],[-0.0,0.0,2.51782692]],"pbc":[true,true,true],"a":2.5178271667719256,"b":2.5178269134954783,"c":2.51782692,"alpha":59.99999991454224,"beta":60.00000324214051,"gamma":59.9999988338285,"volume":11.286587893379405},"properties":{},"sites":[{"species":[{"element":"C","occu":1}],"abc":[0.875,0.875,0.875],"xyz":[2.54391942,1.7988224012499998,4.40619711],"properties":{"magmom":0.0},"label":"C"},{"species":[{"element":"C","occu":1}],"abc":[0.125,0.125,0.125],"xyz":[0.36341706,0.25697462875,0.62945673],"properties":{"magmom":0.0},"label":"C"}]}}],"meta":{"api_version":"0.63.2","time_stamp":"2024-02-27T03:47:28.940648","total_doc":1,"max_limit":1000,"default_fields":["material_id"]}}

Describe the solution you'd like

The following should generate a "molecule" from the string above (or a substring, after "structure:").

#include <iostream>

#include <openbabel/obconversion.h>
#include <openbabel/mol.h>

int main(int argc,char **argv)
{
  OBConversion obconversion;
  obconversion.SetInFormat("pymatgen");
  OBMol mol;

  bool notatend = obconversion.Read(&mol, ... string above ... );
}

Describe alternatives you've considered

The Python pymatgen library can read this format, and thanks to its own OpenBabel binding, it can covert to other file formats.

(see example here: https://matgenb.materialsvirtuallab.org/2013/01/01/Molecule.html)

However, this requires the use of Python and can't be done directly with C++.

Additional context

Here it is a full python request using the new Materials Project API to download the structure of the material labeled "mp-66":

>>> import os
>>> import requests

>>> MP_API_KEY="12qlK7tT5WoqaXXXJjKKuPBHZ1ByEG3"

>>> print(requests.get("https://api.materialsproject.org/materials/summary/?material_ids=mp-66&_fields=structure",he
aders={"X-API-KEY": MP_API_KEY}).text)
{"data":[{"structure":{"@module":"pymatgen.core.structure","@class":"Structure","charge":0,"lattice":{"matrix":[[2.18050236,0.0,1.25891346],[0.72683412,2.05579703,1.25891346],[-0.0,0.0,2.51782692]],"pbc":[true,true,true],"a":2.5178271667719256,"b":2.5178269134954783,"c":2.51782692,"alpha":59.99999991454224,"beta":60.00000324214051,"gamma":59.9999988338285,"volume":11.286587893379405},"properties":{},"sites":[{"species":[{"element":"C","occu":1}],"abc":[0.875,0.875,0.875],"xyz":[2.54391942,1.7988224012499998,4.40619711],"properties":{"magmom":0.0},"label":"C"},{"species":[{"element":"C","occu":1}],"abc":[0.125,0.125,0.125],"xyz":[0.36341706,0.25697462875,0.62945673],"properties":{"magmom":0.0},"label":"C"}]}}],"meta":{"api_version":"0.63.2","time_stamp":"2024-02-27T03:47:28.940648","total_doc":1,"max_limit":1000,"default_fields":["material_id"]}}