  Controlling the dissociation of single water molecule on an insulating
surface plays a crucial role in many catalytic reactions. In this Letter, we
have identified the enhanced chemical reactivity of ultrathin MgO(100) films
deposited on Mo(100) substrate that causes water dissociation. We reveal that
the ability to split water on insulating surface closely depends on the lattice
mismatch between ultrathin films and the underlying substrate, and
substrate-induced in-plane tensile strain dramatically results in water
dissociation on MgO(100). Three dissociative adsorption configurations of water
with lower energy are predicted, and the structural transition going from
molecular form to dissociative form is almost barrierless. Our results provide
an effective avenue to achieve water dissociation at the single-molecule level
and shed light on how to tune the chemical reactions of insulating surfaces by
choosing the suitable substrates.
