Starting with rebasing the next PR that can be reviewed – #879, I have spent most of today in updating the PyQuante bridge function in cclib. The preexisting implementation works only with Python 2.x.x and considering that cclib is trying to drop Python 2.x.x in some foreseeable future, it makes sense to update this to newer PyQuante2, which supports Python 2 and 3.

Since this is a bridge as well, the code mostly resembles the cclib2horton bridge, minus the fact that only cclib to pyquante direction is implemented for this bridge. This is because the bridge is of most use for the cclib.method.volume routine, which uses pyquante to take care of the low-level orbital manipulations to obtain charge densities on a grid.

After two PRs that are related to this – PR #893 for new Travis CI configuration and PR #894 for updated bridge – are merged in, the next step would be to update the cclib.method.volume routine itself to continue into writing a sensible test and finally QTAIM charge routine.