Pressure-induced transformations of AgIIF2-towards an 'infinite layer' d9 material

The enthalpy of seven polymorphs of AgF2 has been scrutinized up to 50 GPa using density functional theory ( DFT) calculations. We show that alpha-(AgF2)-F-II ( Pbca, with its puckered- sheet structure and an elongated octahedral 4 + 2 coordination of Ag) transforms above 15 GPa into a layered polymorph d ( Abma). The Jahn - Teller effect persists and the coordination of Ag( II) is of the 4 + 4 type; the Ag - F - Ag bridges are bent. Cubic. structure of the CaF2 type ( Fm_3m),and its Pa3 variant (eta), rutile (zeta), and tetragonal `infinitechain' P4mm structure related to AgFBF4 (epsilon) are not preferred in the entire pressure window that was investigated. Electronic structure of high- pressure d-(AgF2)-F-II form shows features that are characteristic for two- dimensional ( 2D) materials, a prerequisite for high-T-C superconductivity. Our calculations also suggest that experimentally observed hightemperature beta-AgF2 ( Imcm, disproportionated, i. e. a charge- density- wave form, (AgAgF4)-Ag-I-F-III) is indeed metastable; it is slightly endothermic compared to alpha-(AgF2)-F-II.