Figure 2
Diffusional relaxation of water structure in response to the removal of an ion is compared to MD simulations. (a) After ion removal the GFID reconstructed density returns to the bulk value at the origin (black) and in the first hydration shell (red) exponentially with time constants
and 125 fs (solid lines, fit for
), respectively. (b) MD radial distribution function
of water oxygens: 15 different profiles are shown for
, 20, 40,…, 280 fs. (c) Normalized first peak height
, shown as
, is obtained for five ion types. Fit exponential time constants vary from 64 fs (for
) to 86 fs (for
). (d)
from IXS data (open symbols) show underdamped density oscillations for intermolecular distances (
) but not for intramolecular distances (
). For each
value, the corresponding curve from the best-fit DHO model is shown. The temporal period of this mode varies between 250 fs (black bar) and 180 fs (red bar) at (
), consistent with an O-O oscillation (e) For a sinusoidal driving frequency of an amplitude monopole, the steady-state induced density lags by phase
. For
,
can be approximated by the phase lag of a damped, driven harmonic oscillator (solid line). For
, the behavior deviates strongly from the harmonic oscillator.
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