Computing Surface Acidity Constants of Proton Hopping Groups from Density Functional Theory-Based Molecular Dynamics:...

Area of Science:

• Surface Chemistry and Electrochemistry
• Computational Materials Science

Background:

• Proton transfer at metal oxide/water interfaces is crucial for electrochemistry, geochemistry, and environmental science.
• Surface acidity constants are key thermodynamic values, but existing ab initio methods struggle with spontaneous proton hopping.
• The V_rH scheme, imposing harmonic restraints, is unsuitable for systems with fast proton transfer, like SnO2.

Purpose of the Study:

• To introduce and validate an improved restraining scheme (V_rep) for calculating surface acidity constants in systems with spontaneous proton hopping.
• To apply the V_rep scheme to the SnO2(110)/H2O interface to accurately determine its surface acidity and point of zero charge.

Main Methods:

• Development of a V_rep scheme using a Buckingham-type repulsive potential to prevent proton hopping during DFTMD simulations.
• Validation of the V_rep scheme by calculating pKa values for H2O and aqueous HS-.
• Application of the V_rep scheme to compute surface acidity constants at the SnO2(110)/H2O interface.

Main Results:

• The V_rep scheme successfully handles spontaneous proton hopping, enabling accurate calculations.
• The predicted point of zero charge (PZC) for SnO2(110)/H2O is 4.6, showing good agreement with experimental data.
• Intrinsic pKa values for terminal (Sn5cOH2) and bridge (Sn2ObrH+) sites are 4.4 and 4.7, respectively, close to the PZC, indicating partial water dissociation.

Conclusions:

• The V_rep scheme is a robust method for computing surface acidity constants in systems with rapid proton transfer.
• The findings provide crucial insights into the acid-base equilibrium and interfacial water behavior at the SnO2/water interface.
• This computational approach advances the understanding of interfacial proton transfer in various scientific fields.