Ab Initio Molecular Dynamics Study of Dissociation of Water under an Electric Field

The behavior of liquid water under an electric field is a crucial phenomenon in science and engineering.
However, its detailed description at a microscopic level is difficult to achieve experimentally. Here we
report on the first ab initio molecular-dynamics study on water under an electric field.We observe that the
hydrogen-bond length and the molecular orientation are significantly modified at low-to-moderate field
intensities. Fields beyond a threshold of about 0:35 V=A are able to dissociate molecules and sustain
an ionic current via a series of correlated proton jumps. Upon applying even more intense fields
( 1:0 V=A), a 15%-20% fraction of molecules are instantaneously dissociated and the resulting ionic
flow yields a conductance of about 7:8 1 cm1, in good agreement with experimental values. This
result paves the way to quantum-accurate microscopic studies of the effect of electric fields on aqueous
solutions and, thus, to massive applications of ab initio molecular dynamics in neurobiology, electrochemistry,
and hydrogen economy.