Rigid intertetrahedron angular interaction of nonmolecular carbon dioxide solids

We have theoretically investigated several polymeric (nonmolecular) CO2 solids analogous to various phases of SiO2. Our calculations reveal that CO2 differs dramatically from SiO2 because of its rigid intertetrahedron angular interaction. Because of this, we find that a beta-cristobalitelike phase is energetically the favored polymeric CO2 phase rather than quartz, which is preferred in SiO2. The calculated Raman spectrum of beta-cristobalite CO2 shows a dominant A, peak at about 780 cm(-1) at 40 GPa which shifts down to about 640 cm(-1) at 1 GPa. This is consistent with the recent high-pressure experiments of Iota et al.