PolyMG 4-chain system.

(a) Gallium substitutions in the cross-linking calcium positions. (b) Calcium cross-linked 4-chain system. Only the cross-linking positions have been substituted by gallium and the two outer facing Ca-positions (marked in red on (b)) remain. The formation energies for both systems are marked. Carbon atoms are shown in black, oxygen in red, hydrogen in pink, gallium in green and calcium in blue. Bonds to the gallium and calcium ions are shown as green and blue dashed lines respectively. blue. Bonds to the gallium and calcium ions are shown as green and blue dashed lines respectively. (ZIP)