Carbon Dioxide under Earth Mantle Conditions: From a Molecular Liquid through a Reactive Fluid to Polymeric Regimes

Abstract

In both its gaseous and condensed forms, carbon dioxide has an everincreasing impact on Earth's chemistry and human life and activities. However, many aspects of its high-pressure phase diagram remain unclear. In this work, we present a complete structural characterization of carbon dioxide fluids under geological conditions using extensive ab initio molecular dynamics simulations throughout a wide pressure and temperature range, corresponding to Earth's lower mantle. We identify and describe four different disordered regimes, including two polymeric forms and two molecular ones, all within the geothermal conditions of the lower mantle. At pressures below 40 GPa, we find that the molecular liquid becomes very reactive above 2000 K: the C−O double bond routinely breaks, resulting in small and transient chains composed of CO 2 units and frequently leading to an exchange of oxygen atoms between molecules. At higher pressures, in addition to the polymeric fluid previously reported at 3000 K, we find a polymeric system with glass-like behavior at lower temperatures, suggesting a complex interplay between kinetics and stability.

Computational high‐pressure chemistry: Ab initio simulations of atoms, molecules, and extended materials in the gigapascal regime

“…The focus lies on water, silica melts, HCN, hydrides, carbon-F I G U R E 9 Suggested phase diagram of CO 2 under Earth mantle conditions, based on AIMD simulations. Reproduced with permission from Moog et al, 14 Copyright 2021, American Chemical Society. rich materials, and biological (macro)molecules under pressure.…”

“…Suggested phase diagram of $$$ {\mathrm{CO}}_2 $$$ under Earth mantle conditions, based on AIMD simulations. Reproduced with permission from Moog et al, 14 Copyright 2021, American Chemical Society.…”

“…A recent AIMD study 14 allowed the calculation of the phase diagram of $$$ {\mathrm{CO}}_2 $$$ under Earth mantle conditions (Figure 9). It was found that, below 40 GPa, temperatures above 2000 K are required to make the liquid reactive.…”

“…Using modern high‐pressure technology, 1–7 a plethora of fascinating effects can be induced in chemical systems. Pressure in the gigapascal range (1 GPa $$$ \approx $$$ $$$ {10}^4 $$$ atm) may cause electronic rearrangements at the atomic level, 8,9 allows the synthesis of otherwise unobtainable chemical compounds, 10 gives access to novel crystal structures, 11,12 and can lead to the metallization, 13 polymerization, 14 amorphization 15,16 or decomposition 16 of substances. The experimental method of choice in high‐pressure chemistry, physics, and materials science is the diamond anvil cell (DAC), 1,17,18 which allows the constant application of pressure up to a few hundred GPa 19 .…”

The Mechanical Properties of CO2‐II with Particular Emphasis on Its Auxetic Potential

“…[11][12][13][14][15][16][17][18][19][20][21] A number of studies have also shown the importance of CO 2 as a planetary material. [9,[22][23][24][25] The study of high-pressure chemistry is also of interest to researchers as high pressures could lead to the formation of atypical compounds. [26] One high-pressure polymorph of carbon dioxide is phase II.…”