Transition pathway of CO2 crystals under high pressures

The pressure-induced transitions from molecular to nonmolecular CO2 crystals are systematically investigated by using first-principles lattice dynamics calculations. Geometrically, likely transition pathways are derived from the dynamical instability of the molecular crystals under high pressures. Layered CO2 crystals composed of a two-dimensional network of coiner-sharing CO4 tetrahedra are proposed as metastable products of high-pressure phases obtained through the transition pathways. The layered crystals are similar to phase VI in geometry and Raman spectrum.