Computer simulations are very useful in studying interfacial phenomena. Electronic continuum correction theory (ECC), recently developed by Leontyev and Stuchebrukhov, has been introduced to improve the accuracy of classical molecular dynamics simulations. The main idea of this approach lies in accounting for polarization effects missed in nonpolarizable force fields via reducing the atomic charges of ions by an inverse square root of the electronic contribution to the permittivity, i.e. by a factor close to 75 % in the case of water. With that, van der Waals parameters, which are typically optimized to provide reasonable interatomic distances with full charges, also should be refined. Hence, rescaling partial charges together with fitting Lennard Jones coefficients result in the so-called ECCR (ECC with rescaling) method. Its efficiency was found to yield good agreement of structural and dynamical properties with experimental data for monoatomic and polyatomic ions, organic acids, and proteins. In our recent study, we have shown that the ECCR approach was essential to obtain a good agreement with reference AIMD data when modeling hydrogenoxalate and oxalate ions interacting with water. Here, we provide the first (up to our knowledge) application of the ECCR approach to modeling mineral surfaces, namely, (110) rutile (TiO2), and their interactions with ions and organic molecules. We will investigate (i) a way how to assign the partial charges to surface atoms for a range of surface charge densities following the ECCR concept, (ii) the adsorption of monoatomic cations, namely, Na+, Rb+, and Sr2+, on the neutral and negatively charged rutile surfaces, and (iii) the adsorption of the aforementioned oxalic acid anions on the positively charged surfaces. Our simulation data including adsorbed amounts, density profiles, binding patterns, energy calculations (from advanced sampling techniques, such as potential of mean force determination and metadynamics), and influence of pH will be analyzed and compared against results obtained by surface titration experiments, X-ray reflectivity measurements, and CD-MUSIC surface complexation modeling. In the case of hydrogenoxalate and oxalate, inner-sphere vs. outer-sphere binding motifs will be discussed and compared with information inferred from published ATR-FTIR spectra. This comparison will allow assessing the benefits of the ECCR method for studying similar systems, i.e. modeling of solid-liquid interfaces.

Adsorption of molecular and atomic ions on rutile surfaces from simulations using scaled charges

256th National Meeting (2018)

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