Extended-Solid Phases of Carbon Dioxide at High Pressures*

At high pressures and temperatures, CO$_{2}$ transforms to a series of solid polymorphs with differing crystal structures, intermolecular interactions and chemical bonding. Among them are a number of covalent (extended) solid phases, with crystal structures analogous to SiO$_{2}$ polymorphs. Above 40GPa and 1500K CO$_{2}$ transforms to phase V, a network of corner sharing CO$_{4}$ tetrahedra -- structurally similar to SiO$_{2}$ tridymite. At room temperatures, CO$_{2}$ forms \textit{a-carbonia, }an amorphous extended-solid phase similar to silica glass. Recently, we reported another phase, with a structure resembling that of SiO$_{2}$ stishovite, formed by compressing associated phase II above 50GPa. Here, we present a systematic picture of the structural and bonding diagram of carbon dioxide, focusing on the relationship between its molecular and extended phases at high pressures and temperatures.