Posted a github issue as well here, not sure where you prefer such things to be submitted.
Saw that you did significant work on adding an interface between Avogadro and various force field implementations, including the Python API for XTB. Currently this seems to use just the GFN-FF force field method, in alignment with the other options for optimization. This is fine, but since optimizations with the normal semi-empirical GFN2-xTB are also extremely fast, and the accuracy improvement over force fields is significant, it would be cool to include that. Likewise, it would be cool if the user could run CREST calculations directly from Avogadro, to find low energy conformers prior to doing DFT, in the same way various people I know use SPARTAN.
At the moment you seem to be using the xtb-python API. This is apparently then in turn limited to what is available in the xtb C API. Which I guess mean CREST and things is right out.
Also currently the user has to install python, and install xtb-python using conda, and set up their python environment, which is not something 95% of Avogadro users (lots of students) can even begin with, at least not without their hands being held throughout the process.
I have a suggestion.
Since xtb is completely open source and freely available, would it not be possible to simply package it with Avogadro? And then, on request by the user, run calculations using system calls? As in, complete native integration, as the privileged tool for optimization and calculation?
The license for xtb is LGPL/GPL, so if it was packaged as a dynamically-linked binary it should be ok with the Avogadro license, right? The binaries come to 87 MiB on my PC, which I guess is significant, but it can do a lot!
I suggest this because I find xtb to be a truly excellent tool for general use (as it seems you do too based on e.g. this thread), and I really think it would be great for chemical education and open-source chemistry if the use of it was widely accessible via a GUI, especially one as widely distributed as Avo.
Alternatively, I have some intermediate-level Python, including a little PyQt/PySide, but no experience with C++. Do you reckon making an optional add-on or plugin that can be downloaded and set up with one click, that included the xtb binary, would be a) technically feasible and b) within my capabilities to contribute?
Of course it would also be an option to have an interface to xtb go via the interface you built in for force fields in 1.98, but then it would have to not refer exclusively to force fields all the time!
I think effectively making Avogadro a portal to xtb for non-computational chemists would really give a sort of synergistic benefit to both tools.