An ab initio study on the transition path of carbon dioxide at high pressure: evidence for a new intermediate P(4)over-barm2 phase

Abstract

The structural and dynamical behaviour of seventeen solid polymorph of the non-molecular CO2 compound was evaluated using the full potential linear augmented plane wave method (FP-LAPW) in the framework of density functional theory within the generalized gradient approximation (GGA-PBEsol). We showed the presence of stable non-molecular solid CO2 compound, which has the phase as the most energetically stable phase. The phase of the CO2 compound under pressure undergoes phase transition to the rutile phase at P ≈ 5 GPa, while the phase was found to be dynamically unstable. Also, the α-cristobalite phase was found to be dynamically unstable with imaginary mode in the phonon dispersion curves. We showed that the phase exist at P ≈ 11 GPa and undergoes phase transition to the tetragonal phase a high pressure of P ≈ 168 GPa Thus, the transition path for the non-molecular solid CO2 is given as shown below