FCclasses (release 2.1, October 2009)

FCclasses is a Fortran 77 code for the computation of vibrationally resolved electronic absorption, emission and circular dichroism spectra. It implements a time-independent method described in ref. 1-4.

The method works in harmonic approximation including the normal mode Duschinsky mixing. Equilibrium geometries, normal modes and their frequencies are read from input files and they can therefore be computed by any suitable electronic method. Vibronic transitions are partitioned in classes Cn, depending on the number "n" of modes simultaneously excited in the final state. For each class, the codes selects automatically the relevant vibronic transitions through an a priori estimate of their intensity, without imposing limitations on the spectral energy window.

FCclasses includes the temperature effect and it is able to treat both Condon transitions (where the transition dipoles are independent of the nuclear coordinates) and Herzberg-Teller transitions (where the transition dipoles are assumed to be linearly dependent on the nuclear coordinates). In numerous tests the code has proved to be fast and efficient.

Bug fixed, March 2017 Two bugs have been fixed and a new tgz file is available filing the form below. The first bug concerned the printed units for emission spectra and emission lifetimes that were wrong. The second bug potentially affected the convoluted spectrum printed out for finite temperature calculations. More specifically, the so called n-0 transitions were properly computed and the stick bands properly printed out. However, erroneously their contribution on the convoluted spectra (usually minor, especially at low- resolution) was not included.

For further information please contact Fabrizio Santoro.


    Please fill in the form below to receive via mail the link for downloading
April M. Van Winkle and John W. Silzel at Biola University, modified the code to run it in parallel. They kindly made available their version of the code. For further information please click FCclasses21P

List of the references that should be cited in any article whose results are obtained, also partially, by using FCclasses:

    Method's development


  1. F. Santoro, R. Improta, A. Lami, J. Bloino, V.Barone,
    Effective method to compute Franck-Condon integrals for optical spectra of large molecules in solution
    J. Chem. Phys. 126, 084509-(1/13) (2007)., ibidem
    J. Chem. Phys. 126, 169903 (2007).

  2. F. Santoro, FCclasses: A Fortran 77 Code; 2008. (available via the Internet at http://www.pi.iccom.cnr.it/fcclasses; last accessed day/month/year)

  3. Additionally:

    If calculations at finite temperature have been performed, you should cite also:
  4. F. Santoro, R. Improta, A. Lami, V. Barone,
    An effective method to compute vibrationally resolved optical spectra of large molecules at finite temperature in the gas-phase and in solution,
    J. Chem. Phys. 126, 184102-(1/11) (2007)


  5. If calculations including Herzberg-Teller effects have been performed, you should cite also:
  6. F. Santoro, R. Improta, A. Lami, J. Bloino, V.Barone
    Effective method for the computation of optical spectra of large molecules at finite temperature including the Duschinsky and Herzberg-Teller effect. The Qx band of porphyrin as a case study,
    J. Chem. Phys. 128, 224311-(1/17) (2008)


  7. If ECD spectra have been computed, you should cite also:
  8. F. Santoro, V. Barone
    Computational approach to the study of the lineshape of absorption and electronic circular dichroism spectra,
    Int. J. Quantum. Chem. in press, DOI:10.1002/qua.22197