Comparative study of external electric field and potential effects on liquid water ions

S Bonakala and MI Hasan, MOLECULAR PHYSICS (2021).

DOI: 10.1080/00268976.2021.1998689

Molecular dynamics simulations were used extensively in the last decades to study the influence of an external electric field on many physical processes in water, including mobility of ions, field-induced vaporisation, and electrowetting. In most of these studies, the electric field was applied as an external force to all atoms in the simulation. While such an approach is intuitive and straightforward, it neither captures the shielding of the electric field by water nor any interfacial effect. The Constant Electrode Potential Method (CPM) allows for an external electric field to be applied on a system level, resembling experimental settings and accounting for shielding effects by water. In this work, the CPM method has been implemented to study the influence of an external electric field on the surface tension of water and to compare that to the conventional method, in addition to computing the interfacial mobilities of Na+ and Cl- ions at a liquid-vapor interface. The two approaches yield a similar trend of surface tension variation with the electric field. The CPM method predicts a weaker variation in the surface tension in comparison to that of the conventional method, with the maximum reported difference being 36% of the surface tension value.

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