Absorption (upper panels) and scattering (lower panels) opacities of ice-dust grains assuming compact (left) and porous ices (right). Lines in black are the opacities assuming the water ice refractive index derived in this paper, for instance, assuming n_700nm = 1.16 (NK1), whereas red curves show the opacities calculated using n_700nm = 1.32 (NK2). The small panels below the large ones show the variation between the two opacities in percentage values. A small offset is performed on the absorption opacities for better readability. No offset is applied to the scattering opacity. Zoomed-in images of the rectangular regions indicated by the grey dotted boxes are provided in Fig. 5.