Speaker
Description
Modelling of dielectric interfaces remains one of the central challenges in computational chemistry. Liquid-liquid and liquid-gas interfaces have so far received relatively little attention, compared to solid-liquid and solid-gas. We present a new method for efficient simulations of large organic adsorbates at liquid-liquid and liquid-gas interfaces. The adsorbate is treated on the density-functional theory level, fully accounting for its electronic structure. Simulating a large number of solvent molecules explicitly at this first-principles level of theory, however, is not computationally tractable. We therefore resort to an implicit solvation approach, where the solvent is treated as a structureless dielectric medium, and model the interface as the boundary of two semi-infinite media with different dielectric constant $\epsilon$. For this we specifically advance the multipole-expansion (MPE) method to account for differing $\epsilon$ along the so-called solvation cavity surrounding the adsorbate. Additionally, we introduce a multi-center expansion of the dielectric response. While the previous version of the MPE method could solve the electrostatic problem only for small solute molecules up to $\approx$ 10 non-hydrogen atoms, this development now allows us to more accurately capture larger molecules with an overall non-convex hull, with electrostatic interaction energies converged up to few meV. On the contrary, validating first results of our model for octanoid acid at a water-gas interface by explicit force-field level molecular dynamics simulations provides insight into the role of the atomistic structure of the solvent in the adsorption. The latter can be incorporated into our implicit model by explicit inclusion of a small number of solvent molecules, in a future development. Furthermore, we plan to extend our model to also account for the liquid phase at solid-liquid interfaces, enabling simulations of catalytically active surfaces.
