Rigid intertetrahedron angular interaction of nonmolecular carbon dioxide solids

We have theoretically investigated several polymeric (nonmolecular) CO2 sol ids analogous to various phases of SiO2. Our calculations reveal that CO2 d iffers dramatically from SiO2 because of its rigid intertetrahedron angular interaction. Because of this, we find that a beta-cristobalitelike phase i s energetically the favored polymeric CO2 phase rather than quartz, which i s 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 t o about 640 cm(-1) at 1 GPa. This is consistent with the recent high-pressu re experiments of Iota et al.