  We present a novel approach to calculate molecular IR spectra based on
semiclassical molecular dynamics. The main advance from a previous
semiclassical method [M. Micciarelli, R. Conte, J. Suarez, M. Ceotto J. Chem.
Phys. 149, 064115 (2018)] consists in the possibility to avoid state-to-state
calculations making applications to systems characterized by sizable densities
of vibrational states feasible. Furthermore, this new method accounts not only
for positions and intensities of the several absorption bands which make up the
IR spectrum, but also for their shapes. We show that accurate semiclassical IR
spectra including quantum effects and anharmonicities for both frequencies and
intensities can be obtained starting from semiclassical power spectra. The
approach is first tested against the water molecule, and then applied to the
10-atom glycine aminoacid.
