Surface Acidity Of A SnO₂ Water Interface From Density Functional Theory Based Molecular Dynamics

Acidity constants are one of the most important physical quantities that determine the thermochemistry of acid-base reactions,and have been extensively studied both by experiment and theoretical calculation.When submersed in water,a number of metal oxides form a significant surface charge of which the sign and magnitude is dependent on the pH of the solvent.Also,proton transfer is crucial in modulating electron transfer via redox potential leveling in proton coupled electron transfer(PCET)reactions ubiquitous in inorganic,organic and biological systems.It would be useful to accurately calculate acidity constants.In literature,there are two popular empirical models estimating pKa's,MUSIC models and SBE model.Alternatively,a first principles method developed by Sprik and coworkers,combines density functional theory molecular dynamics and free energy perturbation theory for computing acidity constants without the need for any inputs from experiment.While this method can only calculates those systems that no water dissociated.In this account,it enables us further development this method for calculating water dissociated systems:1.Introduce the repulsive potentials,ensure the form and exact parameters of this repulsive potential according to analyze O-H bond distance and radial distribution function(RDF).2.Apply this method to solution systems:H2O and HS".The pKa we obtained for H2O is 14.07,for HS-is 16.95,those values agree well with the experiments results of 14.0 and 17.5.3.Apply to SnO2(110)/H2O interface:The pKa for TiOH2 and Ti2Ob,are 2.2 and 5.7,respectively.Giving rise to a point of zero charge(PZC)is 4.5.Compared to experiment value 3.8-5.5,it coincide well with the computational results.