A further 8 meV/atom reduction in energy is found when the primitive cell is increased to 32 atoms due to a greater number of cation configurations being allowed. The lowest configuration is the centrosymmetric (antipolar) P 2 1 /c space group where the cations are arranged in a zigzag -Sn-Sb-Sb-Sn-(ABBA) configuration along the metal-sulfur chains, as shown in Figure ). In the P 2 1 /c space group, the a vector is doubled and becomes the c vector. In the initial structures, the Sn(polyhedra) cations were centered between the metalsulfur chains and became off-centred when the geometry was relaxed. The off-centering is present in the Cmc2 1 (16-atom) cell, however the Sn(polyhedra)-S bond difference greatly increases from 0.06 Å in the Cmc2 1 cell, to 0.40 Å in the P 2 1 /c (32-atom) cell, due to reduced Sn(polyhedra)-Sb(chain) repulsion facilitated by the ABBA chain ordering (Figure ). This stabilizes the structure through an additional reduction in Madelung energy (Table ) and an increase in bonding between the Sn(polyhedra) and neighbouring anions.