Electronic structure calculations of liquid-solid interfaces: Combination of density functional theory and modified Poisson-Boltzmann theory

A robust and efficient computational method for electronic structure calculations of liquid-solid interfaces is presented. The theory employs the density functional theory and a modified Poisson-Boltzmann theory, combining them through a smooth dielectric model function. The free energy, including electrostatic and nonelectrostatic interactions between solutes and the solvation medium, is formulated, and its first derivatives with atomic positions are presented. This methodology is applied to two different topics; one is the potential of zero charge (PZC) of Pt(111), and the other is a poisoning of active sites for the oxygen-reduction reaction (ORR) by interfacial water molecules on Pt(111). The results of the first topic show that induced charge redistributions caused by the adsorption of water molecules form a surface dipole moment that dominates the experimentally observed negative shift in the PZC when platinum is immersed in an aqueous electrolyte. The results of the second topic show the possibility of a decrease in the surface coverage of the first reaction precursor to the ORR due to site blocking by the adsorbed water molecules.