Dielectric continuum models are popular for modeling solvent effects in quantum chemical calculations. The polarizable continuum model (PCM) was originally published exploiting the exact dielectric boundary condition. This is nowadays called DPCM. The conductor-like screening model (COSMO) introduced a simplified and slightly empirical scaled conductor boundary condition, which turned out to reduce the errors resulting from outlying charge. This was implemented in PCM as CPCM. Later, the integral equation formalism (IEFPCM) and the formally identical SS(V)PE model of Chipman introduced a modified dielectric boundary condition combining the dielectric exactness of DPCM with the reduced outlying charge sensitivity of COSMO. In this paper, we demonstrate on two huge data sets of neutral and ionic solutes that no significant difference can be observed between the COSMO and IEFPCM, if the correct scaling factor is chosen for COSMO.

The specific density and molar liquid volume of 40 imidazolium-based ionic liquids were predicted using the COSMO-RS method, a thermodynamic model based on quantum chemistry calculations. A molecular model of ion pairs was proposed to simulate the pure ionic liquid compounds. These ion-paired structures were generated at the B3LYP/6-31++G** computational level by combining the cations 1-methyl- (Mmim+), 1-ethyl- (Emim+), 1-butyl- (Bmim+), 1-hexyl- (Hxmim+), and 1-octyl-3-methylimidazolium (Omim+) with the anions chloride (Cl-), tetrafluoroborate (BF4 -), tetrachloroferrate (FeCl4 -), hexafluorophosphate (PF6 -), bis(trifluoromethanesulfonyl)imide (Tf2N-), methylsulfate (MeSO4 -), ethylsulfate (EtSO4 -), and trifluoromethanesulfonate (CF3SO3 -). Satisfactory agreement with the available experimental measurements was obtained, showing the capability of the current computational approach to describe the effect of the anion nature and cation substituent on the volumetric properties of this family of ionic liquids. Thus, calculated and experimental density values of ionic liquids (and also other common solvents) were fitted by linear regressions with correlation coefficients R > 0.99 and standard deviations SD < 20 kg/m3. Consequently, molar liquid volumes were also predicted very accurately by COSMO-RS, indicating the suitability of the ion-pair model to describe intermolecular interactions of pure ionic liquids. In this sense, the σ-profiles of the ion-paired molecules were used to qualitatively analyze the influence of cation and anion natures of ionic liquids on their volumetric properties. As a result of the analysis, we propose the charge distribution area below the σ-profile (S σ -profile) as a simple a priori parameter to characterize the contributions of cation and anion to the ionic liquid behavior as tool to design solvents.

The quantum chemical Conductor-like Screening Model for Real Solvents (COSMO-RS) method was evaluated as a theoretical framework to computationally investigate the application of room temperature ionic liquids (ILs) in absorptive technologies for capturing CO2 from power plant emissions to efficiently reduce both experimental efforts and time consumption. First, different molecular models to simulate ILs and computational methods in geometry calculations were investigated to optimize the COSMO-RS capability to predict Henry’s Law coefficients using a demanding solubility sample test with 35 gaseous solute-IL systems and 20 CO2−IL systems. The simulation results were in good agreement with experimental data, indicating that using an ion-pair molecular model optimized in a gas-phase environment allows a finer COSMO-RS description of the IL structure influence on the CO2 and other solutes solubilities. Moreover, the COSMO-RS methodology was used for the first time to achieve a deeper insight into the behavior of the solubility of CO2 in ILs from a molecular point of view. For this purpose, further analyses of the energetic intermolecular interactions between CO2 and ILs were performed by COSMO-RS, revealing that the van der Waals forces associated with the solute in the liquid phase determine the absorption capacity of CO2 in ILs, which is measured in terms of Henry’s Law coefficients. These findings were finally driven by a rational screening over 170 ILs with COSMO-RS to design new ILs that enhance CO2 capture by physical absorption.

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