Molecular simulation calculates the number of adsorbed ions at charged surfaces

Charged surfaces in contact with solutions are commonplace in physical systems ranging from geological formations to rechargeable batteries. While there exist models for simulating these systems, each of them comes with certain advantages and limitations. For example, molecular simulations used to calculate the motion of individual molecules can often struggle to predict the number of ions adsorbed by charged surfaces from the solution.

Sayer and Cox present a molecular simulation approach for charged surfaces in contact with an electrolyte solution. They investigated the effect of different electrostatic boundary conditions, such as ion distributions and integrated surface charge densities, for polar crystal surfaces in contact with an aqueous solution.

The researchers built on the “finite field” approach. By imposing an electric displacement field (D) in the slab geometry typically used in simulations, the researchers were able to obtain sensible surface charge densities using relatively little computational resources.

“We showed not only how D directly determines the overall surface charge, but how this should be chosen for a given system,” said author Stephen Cox. “What surprised us most is how important the correct D is for the clay mineral kaolinite that we looked at.”

Next, the researchers plan to use this approach to determine and predict the most stable structures for polar crystal surfaces in a solution environment, which has implications for simulations of charged interfaces in contact with an electrolyte solution. A better understanding of how a solution environment affects crystal formation will have broad applications, such as for the pharmaceutical industry.

Source: “Macroscopic surface charges from microscopic simulations,” by Thomas Sayer and Stephen J. Cox, Journal of Chemical Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0022596 .

This paper is part of the open 2020 JCP Emerging Investigators Special Collection, learn more here . Submission Deadline: December 31, 2020.