Ab-initio structure and dynamics of supercritical CO2

TL;DR

This study uses subsystem DFT to analyze the structure and dynamics of supercritical CO2, providing insights that align well with experimental data and demonstrating the method's efficiency for modeling such fluids.

Contribution

The paper introduces the application of subsystem DFT to simulate supercritical CO2, enabling finite-size and finite-time analysis with improved computational efficiency.

Findings

CO2 molecules in supercritical fluid are bent with an average OCO angle of 175.8 degrees.

The T-shape dimer configuration is the most prevalent.

Simulations agree with neutron diffraction experiments on structure and diffusion.

Abstract

Green technologies rely on green solvents and fluids. Among them, supercritical CO2 already finds many important applications. The molecular level understanding of the dynamics and structure of this supercritical fluid is a prerequisite to rational design of future green technologies. Unfortunately, the commonly employed Kohn-Sham DFT is too computationally demanding to produce meaningfully converged dynamics within a reasonable time and with a reasonable computational effort. Thanks to subsystem DFT, we analyze finite-size effects by considering simulations cells of varying sizes (up to 256 independent molecules in the cell) and finite-time effects by running 100 ps-long trajectories. We find that the simulations are in reasonable and semiquantitative agreement with the available neutron diffraction experiments and that, as opposed to the gas phase, the CO2 molecules in the fluid are bent with an average OCO angle of 175.8 degrees. Our simulations also confirm that the dimer T-shape is the most prevalent configuration. Our results further strengthen the experiment-simulation agreement for this fluid when comparing radial distribution functions and diffusion coefficient, confirming subsystem DFT as a viable tool for modeling structure and dynamics of condensed-phase systems.