Hi all,

I've been using OpenMM to run simulations for the past couple of years. Unlike other tools, OpenMM does not write a 'topology' file (e.g. .gro, .prmtop) but instead creates a Topology object on the fly when loading structures. Because simulation systems tend to be quite large, I've take to use PDBx/mmCIF files as my default file format for writing structures that I use as topologies.

I'd like to start using MDAnalysis but right now this involves jumping through a bunch of hoops to get my topologies in a format that is parseable. It'd be much easier if I could just load a PDBx/mmCIF file as a topology, specially since it's now the default file format for structures in the PDB.

To this end, I've started working on writing a simple PDBxParser class. I wouldn't mind extending it to a PDBxReader/Writer class but that is not necessarily a priority (specially the writer). Would this be an interesting feature to add in your opinion? See the code here, I modeled the class after PDBParser.

Thanks for the great work with the library so far!

EDIT: Since I cannot label issues, I'm just editing the title of the issue for now to make it clear!