I have just started using orca, the transition that gives a close match to the experimental spectra has f=0. I realised i need to factor in vibronic coupling, but i am confused on how to write the input file.

I am using this for geometry opt and frequency

! UKS PBE0 GD3BJ def2TZVP Opt Freq TightSCF

Any help would be appreciated!

Thanks