  The fully polarizable QM/MM approach based on fluctuating charges and
fluctuating dipoles, named QM/FQF{\mu} (J. Chem. Theory Comput. 2019, 15,
2233-2245), is extended to the evaluation of nuclear gradients and the
calculation of IR spectra of molecular systems in condensed phase. To this end,
analytical equations defining first and second energy derivatives with respect
to nuclear coordinates are derived and discussed. The potentialities of the
approach are shown by applying the model to the calculation of IR spectra of
Methlyoxirane, Glycidol and Gallic Acid in aqueous solution. The results are
compared with the continuum QM/PCM and the polarizable QM/FQ, which is based on
Fluctuating Charges only.
