Following this, we assessed the model predicted by our DFT and MC calculations, where the Sn and Sb cations are swapped, resulting in Sn residing on the split site (polyhedron), while the other cation position (chain) is shared between Sn and Sb. We find a slight improvement of the refinement parameters (R 1 = 1.6 %, wR 2 = 3.6 %, GoF = 1.13, corresponding to relative improvements of 5-27%), but more significantly, a smoother residual electron density (0.738 > ∆e -/ Å3 > -0.974, a relative improvement of 35%) as compared to the conventional model (Sn 2 S 2 chains rather than Sn 0.5 Sb 0.5 S 2 ). In addition to these improvements in the refinement, we find the bond valence sums (BVS) for the cations in the conventional model are significantly too small for Sb 3+ (+1.90) and too large for Sn 2+ (+2.29). This means the bonds around the Sb position are longer than expected from the bond valence concept, while those involving Sn 2+ are shorter than expected. When Sn and Sb are switched, however, the BVS for Sb 3+ (+2.84) and Sn 2+ (+1.92 and +2.00) are much closer to their expected values (i.e. oxidation states). This notable difference is mainly due to the greater S 2 -coordination of highly charged Sb 3+ in the M 2 S 2 chains (as opposed to the MI 6 polyhedron) along with shorter Sb-S bonds than Sn-S bonds. Accumulating the refinement values and the BVS values, we can conclude with some confidence that our DFT+CE disordered Cmcm structure is indeed the room-temperature crystal structure for Sn 2 SbS 2 I 3 .