Ab initio-enabled phase transition prediction of solid carbon dioxide at ultra-high temperatures

Carbon dioxide is one of the fundamental chemical species on Earth, but its solid-phase behavior at high pressures is still far from well understood and some phases remain uncertain or unknown, which increases the challenge to predict its structures. The difficulty of theoretical prediction arises from the high cost of structure screening and the low accuracy of applicable methods. In this study, we employed an ab initio computational study on solid carbon dioxide phases I and VII at high pressure and predicted their structures, energies and phase transition using the second-order Møller-Plesset perturbation (MP2) theory. Compared to the classical force field method and density-functional theory (DFT), MP2 is capable of describing covalent, ionic, hydrogen-bonds, and dispersion interactions accurately. The equation of state, vibrational spectra and Gibbs free energy were calculated, which agree well with the experimental results. We reproduced the structure of phase VII and the predicted phase boundary between phases I and VII occupying the reasonable region in the phase diagram.