Computing the 1H NMR spectrum of a bulk ionic liquid from snapshots of Car-Parrinello molecular dynamics simulations

We have investigated the performance of several computational
protocols in predicting the NMR spectrum of a molecular ion in a
complex liquid phase such as an ionic liquid. To do this, we computed
the proton NMR chemical shifts of the 1-ethyl-3-methylimidazolium
cation [emim]+ in [emim][Cl]. Environmental effects on
the imidazolium ring proton chemical shifts are quite significant
and must be taken into account explicitly. Calculations performed
on the isolated imidazolium cation as well as on the [emim][Cl]
ion pair grossly fail to reproduce the correct spacing between
proton signals. In contrast, calculations performed on clusters extracted
from the trajectory of a Car-Parrinello molecular dynamics
simulation yield very good results.