Overtones and combination bands

[isolated-matrix]

Hi there,

Thankfully, this isn't a bug report (I got pbqff working, thanks to your help!), more of a question.

The original Spectro was able to calculate anharmonic fundamental frequencies and intensities, as well as overtones and combination bands. Is that functionality still there in the Rust implementation of Spectro? And is it possible to calculate these through pbqff, or do we need to modify the Spectro input and run it through Spectro itself to do that (using the QFF generated by pbqff, of course)?

[ntBre]

That's great to hear!

Unfortunately I have not implemented the intensity side of spectro yet, but overtones and combination bands are available through the separate spectro binary. Unfortunately again, that would mean you'd have to build this from source, and we'd likely run into some of the same build issues as here. If you do give that a try, there's a verbose -v flag for my version of spectro that triggers the overtone and combination band output, and you can use the -f flag with the path to the finish.spectro file output by pbqff (if you used normal coordinates) to run from that input format. So the full command from the root of your pbqff run would be

spectro -v -f freqs/finish.spectro

For other coordinate types, pbqff should have generated a normal spectro.in, fort.15, fort.30, and fort.40 files, so you could just run spectro -v freqs/spectro.in or similar.

But beyond all of that, I think the overtones and combination bands should just be in the default pbqff output anyway, so I will try to patch that in the next few days and cut a new release so you can just get the fix here.