  We use molecular dynamics simulations to study the behavior of supercooled
water subject to different stimuli from a diluted azobenzene hydrophobic probe.
When the molecular motor does not fold, it acts as a passive probe, modifying
the structure of water around it, while when the motor is active, it induces
elementary diffusion processes inside the medium acting mainly on the dynamics.
We study two particular densities, the density of ambient water and a lower
density around the ambient pressure ice density, chosen to favor high density
liquid and low density liquid (LDL) water, respectively. We find that the
passive probe induces ever an acceleration or a slowing down of the diffusion
process around it depending on the density of water, while the active probe
induces acceleration only.
  We find a crossover between the diffusion coefficients for the two densities
near the passive probe, around T = 215 K. This dynamical crossover is
associated with a modification of the structure of water near the probe.
Structure calculations show a crossover of the proportion of LDL water around
the same temperature, suggesting that it induces the observed dynamical
crossover. In opposition with these results, the active stimuli increase
diffusion for both densities and decrease the proportion of LDL water at low
temperatures. However, we also find for the active stimuli a crossover of the
LDL proportion between the two densities of study, showing remarkable
similarities between active and passive stimulus results.
