The unfolded phonon dispersions and DoS curves of the filled models are shown in Fig. . In the "rattler" model of filled cage compounds, the fillers introduce localised bands of modes with a narrow dispersion. However, theoretical studies on BaFe4Sb12 have shown that some fillers introduce features into the DoS over a wide range of frequencies. Filling with He introduces a narrow peak into the phonon DoS at ~6 THz, which lies in the phonon bandgap and is suggestive of "rattling" behaviour (this peak has a small spectral weight un the unfolded phonon dispersion and is therefore difficult to discern). The other four fillers introduce broader bands of modes among the lower-frequency optic modes, similar to the Ba filler in BaFe4Sb12. Interestingly, modes associated with Ne appear around 4 THz in NeCo8Sb24, 4-6 THz ArCo8Sb24, and ~3.5-4 THz in the Kr-and Xe-filled systems. None of the curves show any evidence of imaginary modes, suggesting that there are no driving forces for the fillers to move off centre.