The role of errors related to DFT methods in calculations involving ion pairs of ionic liquids

Abstract

Ionic liquids (ILs) play a key role in many chemical applications. As regards the theoretical approach, ILs show added difficulties in calculations due to the composition of the ion pair and to the fact that they are liquids. Although density functional theory (DFT) can treat this kind of systems to predict physico-chemical properties, common versions of these methods fail to perform accurate predictions of geometries, interaction energies, dipole moments, and other properties related to the molecular structure. In these cases, dispersion and self-interaction error (SIE) corrections need to be introduced to improve DFT calculations involving ILs. We show that the inclusion of dispersion is needed to obtain good geometries and accurate interaction energies. SIE needs to be corrected to describe the charges and dipoles in the ion pair correctly. The use of range-separated functionals allows us to obtain interaction energies close to the CCSD(T) level. © 2017 Wiley Periodicals, Inc.

Valence electronic structure of [EMIM][BF4] ionic liquid: photoemission and DFT+D study

“…26,28 Recently, Lage-Estebanez et al showed that traditional DFT without dispersion correction may be poor for the description of ionic liquid ion-pairs. 29 The inability to predict molecular crystal structures is one of the most notorious failures of traditional DFT methods. 30 As pointed out by Valencia et al and other works, DFT (both LDA and GGA) is not particularly suitable for the description of ionic-liquid crystals due to its inherent lack of correct description of the intermolecular dispersive interactions (non-local vdW interactions).…”

“…28 This is not due to the well-known exchange-hole or self-interaction problem of DFT, because the addition of some (correct) HF exchange, as in the case of hybrids, does not signicantly improve the results. 28,29 This may also explain why hybrid functionals failed to correctly describe the outer valence states in [EMIM][BF 4 ] vapor. 6 The M06 functional is oen recommended 28,32 when the dispersion interaction is important, but it offers little improvement (not shown) in the description of the electronic structure of the [EMIM][BF 4 ] vapor.…”

Density Functional Theory Study of Ionic Liquid Adsorption on Circumcoronene Shaped Graphene

“…Grimme et al concluded that the SIE error is almost negligible for three studied ionic pairs [7]. For a larger set of ionic associates, Lage-Estebanez et al showed that the SIE is pronounced in the case of specific combinations of ions, in particular for ionic pairs including halide anions or pyridinium cation [8,10]. Similar studies of a broad set of organic molecules and halide ions indicated that the SIE is notable [11][12][13].…”

Performance of SCAN density functional for a set of ionic liquid ion pairs

“…This indicates that M06‐L describes charge transfer better than SCAN but incorrectly estimates its energetic effect. The relatively good performance of M06‐L even in comparison with hybrid functionals was seen in the work of Lage‐Estebanez et al, where authors related the charge transfer to the self‐interaction error. So, we concluded that the self‐interaction error correction could be used to improve the overall SCAN performance.…”

“…The density functional theory (DFT) methods offer a good trade‐off between speed and accuracy . The success of DFT depends whether employed exchange–correlation functional can adequately describe the system of interest . In practice, the necessity for faster and scalable methods attracts the attention towards pure DFT functionals and prevents the use of generally more accurate yet more expensive hybrid functionals.…”