How to compute Franck-Condon factors

Franck-Condon factors (FCFs) are needed for modeling vibrational progression in electronic spectra. Most often FCFs are needed for computing UV-VIS and photoelectron spectra, but they also enter other workflows (such as ET rate calculations). FCFs can be computed using stand-alone ezSpectrum code:
which smoothly interacts with Q-Chem’s outputs.
The details are described in ezSpectrum manual:

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We updated the the software! ezFCF v.1.0 (formerly known as ezSpectrum) is available for download at

We removed some dependencies, modernized the scripts, and updated the manual.

For a comprehensive overview of the ezSpectra suite (ezFCF and ezDyson) and tutorial, sign up for the upcoming webinar (03/03, 10-11 PST) hosted by Q-Chem:

We just submitted Software Focus article describing the ezSpectra suite (ezFCF and ezDyson). You can download preprint here:

To address some issues raised at the webinar, we prepared a minor update of ezFCF - v1.1 is now available for download at

Paper describing ezSpectra suite is out: