Invited Talk: Pablo OrdejonDFT and QM/MM simulations of electrified interfaces using Non-Equillibrium Green's Functions

Albeit water is the most common and thus most studied solvent, understanding its structure and properties at the surface of materials is still an open problem. Molecular modeling emerges as way to investigate critical technological electrochemical processes involved in developing batteries, fuel cells, anti-corrosion coatings, and many others in which water interacts with metallic, often electrified, surfaces. The latter can be addressed by using the non-equilibrium Green’s functions (NEGF) method, allowing us to consider the effect of the potential applied to the electrodes. Nonetheless, the typical size of the systems required to include a realistic number of water molecules and the time scale one needs to reach to obtain an accurate representation of these processes is prohibitive in computational cost. To tackle that problem, we have used a quantum mechanics/molecular mechanics (QM/MM) approach coupled to the NEGF method as implemented in the SIESTA package to investigate the metal-water interaction, providing a good balance between accuracy and computational cost. We validated our results against full QM calculations and analyzed the performance to evince the gain in using the QM/MM approach, showing that such a method emerges as a viable way of studying way larger systems compared to those currently used to investigate the dynamics of electrified metal-water interfaces. Our approach allows us to study the dynamics of liquid water in contact with electrified surfaces, reaching significantly longer simulations for systems containing hundreds of water molecules, while fully accounting for the electrode’s potential.