  We simulate vibrational strong (VSC) and ultrastrong coupling (V-USC) for
liquid water with classical molecular dynamics simulations. When the cavity
modes are resonantly coupled to the O-H stretch mode of liquid water, the
infrared spectrum shows asymmetric Rabi splitting. The lower polariton (LP) may
be suppressed or enhanced relative to the upper polariton (UP) depending on the
frequency of the cavity mode. Moreover, although the static properties and the
translational diffusion of water are not changed under VSC or V-USC, we do find
the modification of the orientational autocorrelation function of H$_2$O
molecules especially under V-USC, which could play a role in ground-state
chemistry.
