Ab initio molecular-dynamics study of supercritical carbon dioxide

Abstract

Car-Parrinello molecular-dynamics simulations of supercritical carbon dioxide (scCO(2)) have been performed at the temperature of 318.15 K and at the density of 0.703 g/cc in order to understand its microscopic structure and dynamics. Atomic pair correlation functions and structure factors have been obtained and good agreement has been found with experiments. In the supercritical state the CO(2) molecule is marginally nonlinear, and thus possesses a dipole moment. Analyses of angle distributions between near neighbor molecules reveal the existence of configurations with pairs of molecules in the distorted T-shaped geometry. The reorientational dynamics of carbon dioxide molecules, investigated through first- and second-order time correlation functions, exhibit time constants of 620 and 268 fs, respectively, in good agreement with nuclear magnetic resonance experiments. The intramolecular vibrations of CO(2) have been examined through an analysis of the velocity autocorrelation function of the atoms. These reveal a red shift in the frequency spectrum relative to that of an isolated molecule, consistent with experiments on scCO(2). The results have also been compared to classical molecular-dynamics calculations employing an empirical potential.

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

“…9,14,17 In particular, a comprehensive analysis of the bond angle distribution of CO 2 in the gas and condensed phases was reported by Anderson et al 14 It has been verified that an increase of the temperature from 375 to 673 K or the inclusion of quantum effects leads to a significant broadening of the distributions related to the CO bond distances. These authors also notice that CO 2 should not be viewed as a nonlinear molecule, although it could be represented by a flexible model with an equilibrium angle of 180 • .…”

“…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.…”

Electronic absorption spectra and nonlinear optical properties of CO2 molecular aggregates: A quantum chemical study

“…CO 2 molecule in supercritical phase shows unique characteristics of liquid-like density and gas-like diffusivity in addition to its nontoxic behaviour, as observed in neutron diffraction experiments. [14][15][16] It has been observed in some earlier studies that, due to close proximity of the monomers in these dense phases, the CO 2 molecules no longer remain linear, [17][18][19][20] giving rise to instantaneous dipole moment. Thus we believe, which can be understood in the light of their linear and nonlinear optical response functions.…”

“…We have arranged several single molecular optimized structures in different special orientations and optimized further the molecular aggregates to obtain the cluster geometry, which can be seen possibly in dense CO 2 phases like supercritical one. [17][18][19] The calculated binding energies for these molecular assemblies are given in table 1. As can be seen, the dimer with slipped parallel geometry (D1) is slightly stabler than the T-shape one (D2).…”

Controlled/living heterogeneous radical polymerization in supercritical carbon dioxide

“…36,48,49 The CO 2 molecule has zero permanent dipole moment, 50 but has been reported to be marginally nonlinear (thus having a weak dipole moment) in the supercritical state. 51 Despite its zero (or close to zero in scCO 2 ) dipole moment and low dielectric constant, scCO 2 cannot be considered a nonpolar solvent comparable to alkanes. 50,52 ScCO 2 has been characterized as having a polarizability similar to methane, 46 with a significant quadrupole moment that operates over much shorter distances than dipole interactions.…”