  We characterized the structural and dynamical properties of the quasi-liquid
layer (QLL) at the surface of ice by molecular dynamics simulations with a
thermodynamically consistent water model. Our simulations show that for three
low-index ice surfaces only the outermost molecular layer presents short-range
and mid-range disorder and is diffusive. The onset temperature for normal
diffusion is much higher than the glass temperature of supercooled water,
although the diffusivity of the QLL is higher than that of bulk water at the
corresponding temperature. The underlying subsurface layers impose an ordered
template, which produces a regular patterning of the ice/water interface at any
temperature, and is responsible for the major differences between QLL and bulk
water, especially for what concern the dynamics and the mid-range structure of
the hydrogen-bonded network. Our work highlights the need of a holistic
approach to the characterization of QLL, as a single experimental technique may
probe only one specific feature, missing part of the complexity of this
fascinating system.
