Structural evolution in high-pressure amorphousCO2fromab initiomolecular dynamics

Abstract

By employing ab initio molecular dynamics simulations at constant pressure we investigated behavior of amorphous carbon dioxide between 0-100 GPa and 200-500 K. We focused on 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 proportion of three and four-coordinated carbon atoms. Besides that we also found a new mixed molecular-polymeric form that shows pronounced metastability at certain conditions. The observed behavior suggests CO2 as possible candidate for polyamorphism. We discuss structural and physical properties of the observed amorphous forms as well as their relations to crystalline phases.

A first principles approach to the electronic properties of liquid and supercritical CO2

“…Recent researches also emphasize the interest in the combination of subcritical and supercritical CO 2 with ionic liquids 6 which may lead to the design of sophisticated multiphasic reaction environments. 6 Numerous investigations on the structure, [9][10][11][12][13][14][15][16][17][18][19] dynamics, 9,17 Raman spectrum, [20][21][22][23] and thermochemical properties 24-31 of CO 2 were reported. A very recent work discusses the absorption of CO 2 in a protic ionic liquid.…”

Structural evolution of amorphous polymeric nitrogen from ab initio molecular dynamics simulations and evolutionary search

“…To our knowledge, a comprehensive analysis of structural evolution upon decompression from pressure of order of 100 GPa down to ambient pressure based on state-ofthe-art ab initio simulations has not been performed for a-N. We mention that ab initio MD studies of structural evolution of amorphous phases of sulfur and CO 2 were performed by some of us in Refs. [27] and [28].…”

High-Pressure Structural Evolution of Disordered Polymeric CS2

“…The general high-pressure trend of these compounds is to increase the coordination of the cation by the anion in typical pressure ranges of several to tens of GPa. Indeed, it is well established that the coordination goes from 4 to 6 in SiO 2 , − GeO 2 , and SiS 2 , − and from 2 to mixed 3–4 and pure 4 in nonmolecular amorphous and crystalline CO 2 , respectively. − Furthermore, in the multi-Mbar, CO 2 is also predicted to exhibit 6-fold coordination . At variance with the above-mentioned systems, CS 2 is a strongly metastable substance, even in the molecular state under ambient conditions.…”