Predictions of Physicochemical Properties of Ionic Liquids with DFT

Abstract

Nowadays, density functional theory (DFT)-based high-throughput computational approach is becoming more efficient and, thus, attractive for finding advanced materials for electrochemical applications. In this work, we illustrate how theoretical models, computational methods, and informatics techniques can be put together to form a simple DFT-based throughput computational workflow for predicting physicochemical properties of room-temperature ionic liquids. The developed workflow has been used for screening a set of 48 ionic pairs and for analyzing the gathered data. The predicted relative electrochemical stabilities, ionic charges and dynamic properties of the investigated ionic liquids are discussed in the light of their potential practical applications.

Insights into Ionic Liquid/Aromatic Systems from NMR Spectroscopy: How Water Affects Solubility and Intermolecular Interactions

“…The aromatic ring structures in pyridinium cations present a high density electron cloud, similar to that of the aromatic hydrocarbons, and a larger dipole moment which strengths the cation‐aromatic solute interaction. The imidazolium cations also have an aromatic structure due to the lone pair of the nitrogen, but their smaller effective positive charge leads to a lower aromatic solubility . An increase in the alkyl chain length promotes cation‐anion separation and enhances the hydrocarbon solubility because of the decrease in the polarity of the ionic liquid cation, the increase in its asymmetry, and the free volume of the IL .…”

“…The imidazolium cations also have an aromatic structure due to the lone pair of the nitrogen, but their smaller effective positive charge leads to a lower aromatic solubility. [31] An increase in the alkyl chain length promotes cation-anion separation and enhances the hydrocarbon solubility because of the decrease in the polarity of the ionic liquid cation, the increase in its asymmetry, and the free volume of the IL. [17,35,36] An evaluation of the chemical environment of the IL protons at the highest hydrocarbon concentration has been made by 1 H NMR spectroscopy.…”

Predicting Melting Points of Biofriendly Choline-Based Ionic Liquids with Molecular Dynamics

“…In the work by Zhang and Maginn [18], the IL force field charges used to test different methods were obtained similarly to our initial DFT CHELPG charges, where the ionic charges are forced to be ±1 e. In current work, we observed large errors when using these partial charges ( Table 3). The situation improved slightly with scaling the charges uniformly down with the factor of 0.8-a typical value obtained in DFT calculations [43,60]. Arbitrary down-scaling is better than using charges of unity, but an accurate charge distribution is also required as demonstrated in the previous works [61][62][63].…”

“…However, arbitrarily reducing the partial charges is not justifiable and still led to overestimated melting point predictions. Partial charge transfer manifests itself in DFT calculations of large sets of ion pairs [30,42,43]. Yet, as previous studies have shown, larger associates are require to obtain more realistic ionic charges and partial charge distributions within ions [44,45].…”

Special Issue “50th Anniversary of the Kohn–Sham Theory—Advances in Density Functional Theory”

“…In their approach, the different behavior for such a reaction-either in gas phase or in aqueous solution-can be properly described. There is a discussion by Karu et al [14] of relative electrochemical stabilities, ionic charges and dynamic properties of ionic liquids in the light of their potential practical applications. For a set of 48 ionic pairs the properties for practical electrochemical applications were tested based on a combination of DFT data and informatics techniques using a computational workflow.…”