  Interfacial water on transition metal oxides such as TiO$_2$ has been widely
studied because of their structural complexity and scientific relevance in e.g.
photocatalysis and ice growth. Using ab initio molecular dynamics, we find that
interfacial water on anatase (101) surface features an unconventional fluxional
structure with reduced contact layer density. The density reduction and
flexibility of interfacial water are induced by oxygen vacancy defects deeply
located in the subsurface. Our study proposes a fresh perspective of the
anatase/water interface, raising the importance of non-trivial long-range
effects caused by deep defects. These often-neglected effects highlight the
necessity and challenges of the state-of-the-art simulation and experimental
probing of solid liquid interfaces.
