  We investigated the stability of polymeric CO2 over a wide range of
pressures, temperatures, and chemical environments. We find that the I-42d
polymeric structure, consisting of a three-dimensional network of corner
sharing CO4 tetrahedra, forms at 40-140 GPa and from a CO-N2 mixture at 39 GPa.
An exceptional stability field of 0 to 286 GPa and 100 to 2500 K is documented
for this structure, making it a viable candidate for planetary interiors. The
stability of the tetrahedral polymeric motif of CO2-V is a consequence of the
rigidity of sp3 hybridized orbitals of carbon in a closed-packed oxygen
sublattice.
