Short Time Dynamics of Ionic Liquids in AIMD-Based Power Spectra

Abstract

Power spectra of several imidazolium-based ionic liquids, 1,3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazolium dicyanamide 5, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium thiocyanate, and 1-butyl-3-methylimidazolium dicyanamide, are presented based on ab initio molecular dynamics simulations. They provide an alternative tool of analysis of several electronic structure-based properties, in particular, those related to the strength of hydrogen bonding in liquids. Moreover, they can be employed to interpret experimental IR or Raman spectra, avoiding the additional calculations required for theoretical IR or Raman spectra. The obtained power spectra are shown to be in good agreement with experimental spectra, and electronic structure properties related to them are analyzed. Further, there are indications for a locality of the power spectra on a relatively short time scale of ≈10 ps or system size of about 8 ion pairs as already speculated in previous work.

Intermolecular interactions, ion solvation, and association in mixtures of 1‐n‐butyl‐3‐methylimidazolium hexafluorophosphate and γ‐butyrolactone: insights from Raman spectroscopy

“…Nonetheless, the lower wavenumber contributions of the C 2 ―H stretching profile are dominated by the strongly H‐bonded configurations. This is also confirmed by the progressive redshift of the ring C―H contributions with increasing anion basicity . The latter observation is admitted by both groups who initiated the debate …”

“…Nevertheless, the latest studies on this issue which use IR spectroscopy of EmimTFSI as single ion pairs in helium nanodroplets or in jet‐cooled IL vapor suggest that both effects contribute to the complex broad low‐wavenumber part of the ring C―H stretching profile which is attributed to the C 2 ―H stretching mode. Ab initio molecular dynamics using a dispersion‐corrected density functional showed that despite the fact that the spectral contributions stemming from the C 2 ―H fragment are revealed at somewhat lower wavenumbers they cover rather broad range strongly overlapping with the C (4,5) ―H contributions. Nonetheless, the lower wavenumber contributions of the C 2 ―H stretching profile are dominated by the strongly H‐bonded configurations.…”

Periodic Arrays of Phosphorene Nanopores as Antidot Lattices with Tunable Properties

“…The power spectrum P ( ω ) is obtained by first performing a molecular dynamics run and then calculating the Fourier transform of the total velocity autocorrelation A v ( τ ): 97 $$A_{\mathrm{v}}false(\tau false)=\sum _{n=1}^{N_{\text{atoms}}}{\int }_{-\infty }^{\infty }\mathrm{normald}t{\overrightarrow{v}}_{n}false(tfalse)·{\overrightarrow{v}}_{n}false(t+\tau false)$$ $$Pfalse(\omega false)=true|m{\int }_{-\infty }^{\infty }\mathrm{normald}\tau A_{\mathrm{v}}false(\tau false){\mathrm{e}}^{-\mathrm{normali}\omega \tau }true|$$…”

Computer simulations of ionic liquids at electrochemical interfaces

“…The most important one is that classical modelling is not suitable for the determination of the potential of zero charge (PZC), which is defined as the value of ∆Ψ for which σ + = σ − = 0 ; of course a value can be extracted from C-V curves but those cannot be compared to experiments because it corresponds to the position of the Fermi level of the electrode, an electronic property which can only be caught at the ab initio level. Ab initio molecular dynamics may provide a solution to this problem in future years 101 , but this technique remains substantially too expensive in computational resources because of the large cells and long relaxation times necessary for the IL interfacial studies -for the moment it is limited to the study of relatively small bulk ionic liquids samples [102][103][104] . The surface charges and the relative potentials fluctuate on long timescales so that their averages are associated with substantial error bars; for example on figure 5.…”