Mixed threefold and fourfold carbon coordination in compressed CO2.
Carbon dioxide (CO2) has been recently reported to possess an amorphous form, named "carbonia," structurally similar to other group-IV oxide glasses. By combining ab initio constant pressure molecular dynamics, density-functional perturbation theory, and experimental IR spectra, we show that carbonia, and possibly also phase VI, is not SiO2-like, and that instead it is partially tetrahedral containing also a sizable amount of carbon in threefold coordination, but no sixfold octahedral coordination. Enthalpic considerations suggest that carbonia is a metastable intermediate state of the transformation of molecular CO2 into fully tetrahedral phases.
International School for Advanced Studies (SISSA), Trieste, Italy.
Javier A
JA
Montoya
Roger
R
Rousseau
Mario
M
Santoro
Federico
F
Gorelli
Sandro
S
Scandolo