Valence electronic structure of [EMIM][B(CN)₄]: ion-pair vs. bulk description

Abstract

The ultraviolet photoelectron spectrum of the [EMIM][B(CN)4] ionic liquid was recorded and simulated using different ab initio ion-pair and bulk calculation methods.

The electronic structure of ionic liquids based on the TFSI anion: A gas phase UPS and DFT study

“…In addition, there is no need for energy scale adjustment other than a constant shift. This is surprising, since in most other cases, the energy scale would benefit from compressing in the case of ion-pair calculations [17,18] or stretching when bulk calculations are performed [37] . The M06 functional needed a 2.0 eV shift and the ωB97X-D functional only needed a 0.3 eV shift to match the experiment.…”

“…The ion-pair approximation assumes that the electronic structure of the ionic liquid is similar to the ion-pairs it consists of. The ion-pair approximation seems to hold for [EMIM][TFSI] [29] but may not be valid for [PYR1,4 or DEME][TFSI], a situation similar to [EMIM][BF4 or B(CN)4][18,37]. Therefore care should be taken when extrapolating results from these gas phase measurements and calculations to the liquid phase.…”

Frontier orbitals and quasiparticle energy levels in ionic liquids

“…In recent years, a number of experimental and theoretical investigations of the electronic structure of ILs have been reported. For example, photoelectron spectroscopy has been used to study the valence band electronic structure of liquid ILs and IL vapors consisting of neutral cation-anion pairs [13][14][15][16][17][18][19] .…”

“…To gain a detailed understanding of the properties of ILs, many groups have carried out calculations based on density-functional theory (DFT) [20][21][22][23][24] . To model photoemission experiments, several studies compared the Kohn-Sham (KS) eigenvalues obtained from DFT calculations to the measured photoelectron spectra 16,17,19,25 . This practice is based on the observation that in many materials KS eigenvalues can be useful approximations to quasiparticle energies that are measured in photoemission spectroscopy.…”

Frontier Orbitals and Quasiparticle Energy Levels in Ionic Liquids

“…For example, photoelectron spectroscopy has been used to study the valence band electronic structure of liquid RTILs and ionic liquid vapours consisting of neutral cation-anion pairs. [13][14][15][16][17][18][19] Computational studies of RTILs have mostly been carried out in the framework of density functional theory (DFT). [13,[19][20][21] Advantages of DFT include its relatively modest computational cost and its ability to predict ground state geometries with good accuracy, as long as dispersion interactions are taken into account.…”