Interestingly, this finite strain difference approach also yields the density at zero pressure ρ 0 which is of 1.16 g cm for the crystal and of in the 1.21 to 1.31 g cm -3 range for the glasses. It is consistent with previous AIMD results and experimental works which showed that glasses have larger ρ 0 than the crystalline phase. However, it should be noted that all densities are smaller than the experimental values of ρ glass = 1.38 g cm -3 (CO 2 physisorption study 66 ) and ρ crystal = 1.22 g cm -3 (crystallographic density 67 ).