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

Abstract

The electronic absorption spectra of liquid and supercritical CO2 (scCO2) are investigated by coupling a many-body energy decomposition scheme to configurations generated by Born-Oppenheimer molecular dynamics. A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies were calculated with time dependent density functional theory. A red-shift of ∼ 0.2 eV relative to the gas-phase monomer is observed for the first electronic absorption maximum in liquid and scCO2. The origin of this shift, which is not very dependent on deviations from the linearity of the CO2 molecule, is mainly related to polarization effects. However, the geometry changes of the CO2 monomer induced by thermal effects and intermolecular interactions in condensed phase lead to the appearance of an average monomeric electric dipole moment〈μ〉= 0.26 ± 0.04 D that is practically the same at liquid and supercritical conditions. The predicted average quadrupole moment for both liquid and scCO2 is〈Θ〉= - 5.5 D Å, which is increased by ∼ -0.9 D Å relative to its gas-phase value. The importance of investigating the electronic properties for a better understanding of the role played by CO2 in supercritical solvation is stressed.

Probing Lewis Acid–Base Interactions with Born–Oppenheimer Molecular Dynamics: The Electronic Absorption Spectrum ofp-Nitroaniline in Supercritical CO2

“…As in previous BOMD studies, 40,57 the vibrational spectrum is presently investigated through the calculation of time correlation functions. For example, the distribution of the ν(C−N) stretching frequency of PNA in scCO 2 can be analyzed by calculating the Fourier transform of the average velocity autocorrelation function defined as C AA (t) = ⟨A(t)…”

Quantum Chemistry with Thermodynamic Condition. A Journey into the Supercritical Region and Approaching the Critical Point

“…However, this is not free from risks and in some cases the use of quantum molecular dynamics may be advisable. 11,12 The possibility of incorporating thermodynamic condition led to great developments in the theoretical description of molecular spectroscopy and reactivity in solution. Solvent effects can be incorporated realistically contributing to a more accurate description of the spectroscopic results but also adding some new aspects such as the calculation of inhomogeneous line broadening.…”

“…Recently there has been an increased theoretical interest in the supercritical region. 11,[13][14][15][16][17] For thermodynamic conditions beyond the critical point, the supercritical region, the fluid exhibits novel characteristics with unusual properties very different from normal and regular liquids. For instance, small changes in the thermodynamic condition of the fluid in the supercritical region change pronouncedly the dielectric constant.…”

Surface‐enhanced Raman scattering properties of Lewis acid–base complexes ofp‐hydroxybenzoic andp‐mercaptobenzoic acids with CO2in the presence of silver

“…Recently, the anomalous red shift of the charge transfer π–π * in p ‐nitroaniline (PNA) was investigated in scCO 2 , and its origin was demonstrated to be related to the LA–LB interactions with neighbor CO 2 molecules . Under supercritical conditions, CO 2 is an important solvent because of its ability to induce significant and controlled modifications on solvated molecules . For these reasons, we also expect obtaining typical effects of LA–LB complexes in the calculated spectra of PHBA and PMBA with CO 2 in the presence of a metal.…”