Comparison of Water Models in Simple Electric Double Layers
Abstract
The three bulk water models (SPCE, TIP4P and ST2) are compared in molecular dynamics simulations of electric double layers consisting of a monovalent ion (Na(+) or Cl(-)), water as solvent, and a flat metal electrode. The goal is to identify features of the double layer that are sensitive to the model and those that are not. The simulations are done with zero external field and one non-zero applied field. All electrostatic image interactions due to the ion and the point charges constituting the water molecules are included in the calculation. All the models give rise to several well defined solvent density oscillations at the metal surface and the first peak in particular can be strongly accentuated by an external electric field. The Na(+) ion occupies a diffuse zone in which its first solvation shell remains intact even when drawn to the electrode by an external field. One striking difference occurs for the ST2 water compared to the other models. In a cathodic external field the Na(+) ion does not concentrate near the electrode. There are also quantitative differences in the electric potential profiles. Effects of replacing Na(+) with Cl(-) are also studied. It was observed that there was less structure in the water density profiles with solvated anions. The Cl(-) ion occupies a diffuse zone that extends to the surface where it makes occasional contact and its solvation shell greatly distorted. In an external field the chloride ion forms a compact layer at the metal with no diffuse component to its distribution. Significant differences in using different water models are observed and are interpreted on the basis of the relative strength of the solvation and the stiffness of the liquid.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 09, 1994
- Accession Number
- ADA284011
Entities
People
- James N. Glosli
- Michael R. Philpott
- Sheng-bai Zhu
Organizations
- International Business Machines Corporation (Armonk, NY)