Terahertz electric field serves as a freeze button for water

Water, as a most common but unique molecule, plays a key role in biological and physical processes, whose properties can be effectively modulated by electric fields. In this work, we use molecular dynamics simulations to investigate the structures and dynamics of bulk water under the influence of terahertz electric fields. The result indicates that the diffusion coefficient of water decreases almost linearly with the increase in field frequency, because the water molecules have to adjust their dipole orientation intensively at high field frequency, which impedes the water motion. Additionally, for a small field frequency the diffusion coefficient is not sensitive to the change in field strength; while at high frequencies it displays an interesting minimum behavior. The minimum translational diffusion coefficient is about one fourth of natural diffusion, suggesting a freezing state of water molecules. In addition, almost the same trend can be seen in the rotational diffusion coefficient. Subsequent analyses of the hydrogen bond number support the behaviors of diffusion coefficient, revealing the two ways that the terahertz electric fields affect the bulk water: clustering and oscillation. Then, we reveal the structural changes of water under terahertz electric field through radial distribution function (RDF), potential of mean force (PMF) and dipole angle, which show the sensitivity to the field frequency and strength. These findings demonstrate that the terahertz electric field is an effective method to modulate the structures and dynamics of water, providing significant new physical insights.