Dust opacity to the 1 and 3 mm from the coagulation model in protostellar cores. The data points in the main panel are retrieved from Ossenkopf & Henning (1994). The blue, orange, and green colors represent the dust grain, dust grain with thin ice mantle, and dust grain with thick ice mantle, respectively. The square and circle line markers represent for the case of volume density of 10⁶ and 10⁸ cm⁻³, respectively. The subpanel zooms in the frequency range of ∼ 0.1−1 THz, i.e., 300 μm to 3 mm. Based on the retrieved data points in a solid line, dust opacity is extrapolated by a power-law form κ_ν ∝ ν^β up to the 3 mm band in a dashed line. The extrapolated dust opacity is κ_{1 mm} = 0.9 ± 0.1 cm²/g and κ_{3 mm} = 0.18 ± 0.02 cm²/g.