Structural evolution in high-pressure amorphous CO_2 from ab initio molecular dynamics

摘要

By employing ab initio molecular dynamics simulations at constant pressure we investigated the behavior of amorphous carbon dioxide between 0 and 100 GPa and 200 and 500 K. We focused on the evolution of the high-pressure polymeric amorphous form known as a-carbonia on its way down to zero pressure, where it eventually converts into a molecular state. During the simulations we observed a spectrum of amorphous forms between two limiting polymeric forms with different proportions of three- and four-coordinated carbon atoms. Besides that we also found a mixed molecular-polymeric form that shows pronounced metastability at certain conditions. The observed behavior suggests CO_2 as a possible candidate for polyamorphism. We discuss the structural and physical properties of the observed amorphous forms as well as their relation to crystalline phases.