Plots of the efficiency of absorption Q_abs(λ) for two exemplary grain shapes with a fractal dimension of D_f = 2.0, different wavelengths λ (rows), and grain sizes a_eff (columns). Solutions are calculated with the DDSCAT code for different values of the number of dipoles N_dip (red dot). The DDSCAT solutions are extrapolated assuming N_dip → ∞ (blue dots). The percentage values represent the error between the extrapolated solutions and the exact solutions of the MSTM code (black cross).