This paper presents some recent results of ab initio calculations of the dynamical properties of GaAs/AlAs superlattices (SL’s) grown along the (001) direction. In particular we will focus on open problems in the interpretation of the experimental thickness-dependence of the zone center longitudinal optical (LO) SL frequencies in the ultrathin (UT) regime, and clarify the origin of the major discrepancy between the measured Raman spectra and the previous theoretical predictions. This will allow us to draw conclusions on structural properties of such systems, and obtain indications on how LO modes can give useful information for characterization also in UT structures.
