CCL:G: Low-progression Franck-Condon transitions

["Tobias Kraemer" <tobias.kraemer(~)mu.ie>]

 Sent to CCL by: "Tobias  Kraemer" [tobias.kraemer_._mu.ie]
 Hello everyone,
 I am interested in calculating vibrationally-resolved spectra in G16. The
 molecule in question is a phthalocyanine (pc) complex. I've followed the
 protocol detailed in the whitepaper by Barone et al., however in the
 final step (generating the spectrum) an error occurs:
      ==================================================
               Calculations of Band Intensities
      ==================================================
  -- To: vibronic fundamental state --
     Spectrum progression:    0.06%
  -- To: single overtones --
     Spectrum progression:    0.71%
  -- To: combinations of  2 simultaneously excited modes --
     Spectrum progression:    4.14%
  ERROR: Low progression after class 2. Total convergence =  4.1%.
         The vibronic spectrum will likely be unreliable. Stopping.
 The whitepaper provides some possible causes, but I'd like to ask for
 some expert opinions here on CCL nonetheless. In the excited state
 optimisation I have included 6 states, of which the gradients for the
 first one are to be followed [TD=(Read,NStates=6,Root=1)].
 There are a good number of keywords listed on the Gaussian16 webpage that
 relate to this type of calculation, and I'd appreciate some guidance on
 the above issue and possible ways around it.
 Thanks for your help, as always much appreciated.
 Kind regards,
 Tobias