  Particle shape and aggregation have a strong influence on the spectral
profiles of infrared phonon bands of solid dust grains. In this paper, we use a
discrete dipole approximation, a cluster-of-spheres code following the
Gerardy-Ausloos approach and a T-matrix method for calculating IR extinction
spectra of aggregates of spherical silicon carbide (SiC) particles. We compare
the results obtained with the three different methods and discuss differences
in the band profiles.
