spectrum ezFCF (formerly known as ezSpectrum) computes stick spectra (photoelectron and photoexcitation) for polyatomic molecules within the double–harmonic approximation.

Franck-Condon factors (FCFs), the overlaps between the initial and target vibrational wavefunctions, can be calculated:

  • in the parallel normal modes approximation as products of one-dimensional harmonic wave functions;
  • including Duschinsky rotations of the normal modes as full-dimensional integralsin full dimensionality including Duschinsky rotations of the normal modes.
In both cases the overlap integrals are computed analytically.

The calculation requires equilibrium geometries, harmonic frequencies, and normal mode vectors for each electronic state, which can be computed by ab initio packages. The key feature of ezFCF is the program–independent xml input. It can be prepared either manually following the format description in the manual and the examples provided, or by running the python script that processes Q-Chem, ACESII, Molpro, GAMESS, Orca, and Gaussian outputs. (We are Gaussian free zone, and encourage everyone to degauss their workplace as well.) The script can be easily modified to process outputs of other programs.

Download ezFCF (includes samples, make_xml.py script, source code, precompiled binaries, and manual.pdf): ezFCF_v1.2.tar.gz

This distribution provides an executable compiled for generic Linux and MacOS 64-bit machines. The program is distributed under GPL license.

The user manual can also be downloaded separately here

To install the Linux or MacOS version, execute:
gzip -d < ezFCF_v1.2.tar.gz | tar xvf -

For a crash-course introduction, watch webinar describing ezSpectra suite by Professor Samer Gozem

Please contact Professor Anna I Krylov (krylov@usc.edu) if you have suggestions, questions, or bugs to report.

To acknowledge ezFCF, use the following citation:
S. Gozem, A. I. Krylov, "The ezSpectra suite: An easy-to-use toolkit for spectroscopy modeling", WIRES CMS, e1546 (2021) and P. Wojcik, S. Gozem, V. Mozhayskiy, and A.I. Krylov, http://iopenshell.usc.edu/downloads


ezSpectrum translated to Belarusian: courtesy of studybounty.com.

ezSpectrum translated to Portuguese: courtesy of Artur Weber.

ezSpectrum translated to Polish: courtesy of StudyCrumb.com.

ezSpectrum translated to Romanian: courtesy of Irina Vasilescu.

ezSpectrum translated to Ukrainian: courtesy of skyclinic.ua.