23954 | Phys. Chem. Chem. Phys., 2018, 20, 23954--23966 This journal is © the Owner Societies 2018 Cite this: Phys. Chem. Chem. Phys., 2018, 20, 23954 Modeling of solid–liquid interfaces using scaled charges: rutile (110) surfaces† Denys Biriukov, a Ondr ˇ ej Kroutil ab and Milan Pr ˇ edota * a Electronic continuum correction (ECC) has been proven to bring significant improvement in the modeling of interactions of ions (especially multivalent) in aqueous solutions. We present a generalization and the first application of this approach to modeling solid–liquid interfaces, which are omnipresent in physical chemistry, geochemistry, and biophysics. Scaling charges of the top layer of surface atoms makes the existing solid models compatible with the ECC models of ions and molecules, allowing the use of modified force fields for a more accurate investigation of interactions of various metal and metal-oxide surfaces with aqueous solutions, including complex biomolecules and multivalent ions. We have reparametrized rutile (110) models with different surface charge densities (from 0 to 0.416 C m 2 ) and adopted/developed scaled charge force fields for ions, namely Na + , Rb + , Sr 2+ , and Cl  . A good agreement of the obtained molecular dynamics (MD) data with X-ray experiments and previously reported MD results was observed, but changes in the occupancy of various adsorption sites were observed and discussed in detail. 1. Introduction Solid–liquid interfaces attract a lot of scientific attention due to the ubiquitous occurrence of adsorption processes in a wide range of natural and industrial environments, since the surface of any material is the principal pathway for its interaction with the surrounding environment. It is well known that chemical reactions between mineral surfaces and aqueous solutions play a crucial role in corrosion, soil production, chemical weathering, degradation of building materials, and transforma- tion of environmental contaminants and pollutants. Therefore, the examination of these phenomena is a challenging task for today’s scientists. Many experimental techniques like reso- nant anomalous X-ray reflectivity and X-ray standing wave measurements, 1,2 nonlinear spectroscopy, 3,4 and flow micro- calorimetric measurements 5 have been applied to explore the properties of different compounds at mineral–fluid interfaces. On the other hand, theoretical approaches such as density functional theory, ab initio molecular dynamics, and classical molecular dynamics (MD) greatly improved the molecular-level understanding of processes occurring at interfaces. 6–10 Titanium dioxide has been a subject of numerous works due to its simplicity and importance in comparison with other minerals being used in nanotechnology and nanoscience. 11 High physical and chemical stability makes TiO 2 nanoparticles of particular interest for many applications in biosensors, 12 consumer production, 13 and medicine. 14,15 Moreover, different forms of titanium surfaces show a high photocatalytic activity. 16 The rutile surface, which is the most stable form of titanium dioxide under ambient conditions, 17 and in particular its predominant (110) stable crystal face, has been a subject of many theoretical and experimental studies, separately and in combination. Numerous studies measured the pH dependence of the surface charge and the point of the zero net charge, 18 multilayer formation of the adsorbed water on the surface, 19 and an electric double layer (EDL) at the interface. 20 Further studies were aimed at the adsorption of ions 21,22 and organic compounds, e.g. dicarboxylic acids, amino acids, and nucleic acids. 23–25 Particular attention was devoted to the hydra- tion of the surface, i.e. water molecules physically adsorbed on the bare terminal Ti atoms or dissociatively chemisorbed to form OH groups at both bridging and terminal sites. 26,27 Other works also provided information about the surface steps and the influence of such defects on the adsorption processes. 28,29 Great contribution to the understanding of the TiO 2 –water interface has been made by MD simulations, 30 both with a classical approach 31,32 and using a reactive force field, where the formation and breaking of covalent bonds are allowed. 33–35 Here, we continue our series of articles focused on modeling a-rutile (110) surfaces interacting with aqueous solutions. a Institute of Physics, Faculty of Science, University of South Bohemia, Branis ˇovska´ 1760, 370 05, C ˇ eske ´ Bude ˇjovice, Czech Republic. E-mail: predota@prf.jcu.cz; Tel: +420 387776258 b Faculty of Chemistry, Materials Research Centre, Brno University of Technology, Purkynˇova 118, 612 00 Brno, Czech Republic † Electronic supplementary information (ESI) available: Gromacs simulation files, comparison of Matsui–Akaogi and Brandt–Lyubartsev potentials for TiO 2 surfaces, ion–water distances from simulations, numbers of species in simula- tions, additional density profiles of water and ions at rutile surfaces of different surface charge densities, and height of ions at surface adsorption sites. See DOI: 10.1039/c8cp04535f Received 17th July 2018, Accepted 31st August 2018 DOI: 10.1039/c8cp04535f rsc.li/pccp PCCP PAPER