Electrified interfaces (EIs) play a crucial role in electrochemical devices and processes, with applications spanning energy technologies, memory devices, corrosion and many others. A major challenge in modelling interfacial processes is the need to perform simulations at a constant potential, which would naturally involve the use of an open-boundary description of the electrons. The hairy probes
(HP) formalism in the weak coupling limit is an efficient open-boundary formalism suitable to describe multi-terminal electrochemical systems. In my doctoral project, I interfaced it within the Kohn-Sham DFT framework in the CP2K computational package. The resulting methodology, the hairy probes DFT (HP-DFT) formalism, enables the efficient DFT modelling of electrochemical systems under direct potential control.
The HP-DFT formalism was benchmarked using parallel-plate capacitor models. The methodology accurately maintained the imposed electrochemical potential difference and correctly represented the physics of parallel-plate capacitors. Additionally, the HP-DFT formalism was successfully used in combination with geometry relaxations and, crucially, AIMD simulations to study the response of water on a Pt(111) surface to applied potentials. Overall, the HP-DFT correctly reproduced key features of Pt(111)/water interface under bias, all while demonstrating high computational efficiency. This widens the scope of AIMD simulations, enabling non-equilibrium AIMD under bias.
Finally, an atomic gold junction model with explicit water layers representing a more complex electrochemical system was considered. The properties of its electrochemical environment were analysed. Given the high computational efficiency demonstrated by the HP-DFT formalism, simulations of this model under potential control are feasible. These simulations can serve as the foundation for studying the effects of the EC environment on the transport properties of these systems.
This work paves the way to make substantial steps forward in understanding EC phenomena by enabling efficient potential control within DFT simulations.