One-dimensional water nanowires induced by electric fields
The self-aggregation of water vapour molecules under external electric fields is systemically investigated by using molecular dynamics simulations. It is found that small water clusters aggregate into one-dimensional water nanowires along the electric field direction. The electric field strength plays a crucial role in tuning the nanowire structure. under relatively weak electric fields such as E = 0.1 V/Å, the square and pentagonal prism-like structures are preferred; when the intermediate strength electric fields are applied (E = 1.0 V/Å), water nanowires featuring a disordered mixing of four-, five- and six-membered rings are formed; an open ordered structure which is reminiscent of two-dimensional (2D) ice is observed when the field strength becomes very high (E > 3.0 V/Å). The bond parameter analysis based on density-functional theory calculations shows that electric field affects anisotropically the conformation of water molecules as well as the hydrogen-bond properties. Along the electric field, the H-O bond is stretched and the hydrogen bond shrinks with field strength in contrast to the changes perpendicular to the electric field. As a result, the hydrogen bonding is enhanced along the electric field. Upon very high electric fields, the anisotropic hydrogen-bond network opens up via breaking the bonds perpendicular to the electric field and ultimately relaxes into a loose quasi-2D ordered network.