Using extensive equilibrium molecular dynamics simulations we determine the
dielectric spectra of aqueous solutions of NaF, NaCl, NaBr, and NaI. The ion-
specific and concentration-dependent shifts of the static dielectric constants
and the dielectric relaxation times match experimental results very well,
which serves as a validation of the classical and non-polarizable ionic force
fields used. The purely ionic contribution to the dielectric response is
negligible, but determines the conductivity of the salt solutions. The ion-
water cross correlation contribution is negative and reduces the total
dielectric response by about 5%-10% for 1 M solutions. The dominating water
dielectric response is decomposed into different water solvation shells and
ion-pair configurations, by this the spectral blue shift and the dielectric
decrement of salt solutions with increasing salt concentration is demonstrated
to be primarily caused by first-solvation shell water. With rising salt
concentration the simulated spectra show more pronounced deviations from a
single-Debye form and can be well described by a Cole-Cole fit, in
quantitative agreement with experiments. Our spectral decomposition into ionic
and different water solvation shell contributions does not render the
individual contributions more Debye-like, this suggests the non-Debye-like
character of the dielectric spectra of salt solutions not to be due to the
superposition of different elementary relaxation processes with different
relaxation times. Rather, the non-Debye-like character is likely to be an
inherent spectral signature of solvation water around ions
