... Absorption cross-sections of PAHs in the optical/UV (top) and infrared (bottom) as suggested by Li Draine (2001, dashed blue), Malloci et al. (2007, dotted green) and this work, with parameters of Table 1 for the ISM (dotted magenta) and for NGC 2023 (full magenta line). ... We present a model for the diffuse interstellar dust that explains the observed wavelength-dependence of extinction, emission, linear and circular polarisation of light. ... Dust grains with radii larger than 6 nm are spheroids....