Fig. 2: Analysis of the IR-data.

a IR peaks for all the materials in the DFPT database, b comparison of finite-difference (FDM) and DFPT phonon frequencies for conventional cells, c space-group distributions of materials with at least one far (blue) and mid (green) IR peaks, d Venn-diagram of the chemistry of materials containing chalcogenides, halides, or pnictides materials, e minimum frequency vs density of the system, and f dimensionality analysis of the far-IR materials.