At the same time, the growth direction inside the vessel is aligned vertically-this insight is only possible by non-invasive tomography of the material inside the glass tube, while also revealing the interior pore structure of the grains. Some plate-shaped crystals can also be seen, which is the result of layer-by-layer growth, when the supersaturation is in a moderate regime. Finally, when the supersaturation further increases, especially in the late cooling period, dendrites will form. Overall, the screw-dislocation-driven growth dominated the initial period when the needles formed, and plates could only form starting from a later period, at which time there was not much empty space available. This is the reason why plate-shaped crystals larger than 1 mm × 0.5 mm are not observed, while the needle-shaped crystals in our tomography data are longer than 5 mm. Figure (f) shows the schematics of all three types of crystals. Finally, the electronic band structure of rhombohedral KBiS 2 is investigated by both theoretical calculation and ultraviolet-visible-near infrared (UV-vis-NIR) spectroscopy measurement, and the results are shown in Figure . Our Kohn-Sham electronic structure without spin-orbit coupling (SOC), shown in Figure (a), agrees well with that reported in an earlier work. In addition, we also quantify the influence of spin-orbit coupling and find that including this effect decreases the band gap by about 0.29 eV (DFT-PBE) and 0.36 eV (HSE06). Several of the lowest conduction bands are split by spin-orbit coupling, see Figure and S5 in the Supporting Information. The valence bands between 2 and 4 eV below the Fermi energy are also affected, but to a lesser extent. These splittings also impact the optical properties of the material, as shown in Fig . Overall, the material shows a pronounced optical anisotropy between the optical conductivities ϵ aa and ϵ cc , as expected for a layered compound. The aforementioned SOC-driven splitting leads to a spectral broadening of both ϵ components on the whole, judged by the total width of the peak from ∼2-6 eV.