  The structure and dynamics of the water/vapor interface is revisited by means
of path-integral and second-generation Car-Parrinello ab-initio molecular
dynamics simulations in conjunction with an instantaneous surface definition
[A. P. Willard and D. Chandler, J. Phys. Chem. B 114, 1954 (2010)]. In
agreement with previous studies, we find that one of the OH bonds of the water
molecules in the topmost layer is pointing out of the water into the vapor
phase, while the orientation of the underlying layer is reversed. Therebetween,
an additional water layer is detected, where the molecules are aligned parallel
to the instantaneous water surface.
