Year: 2026
Type: preprint
Abstract: Incorporating applied electrode potential into density functional theory molecular dynamics simulations of solid-liquid interfaces has developed remarkably in recent years. Current approaches based on constant-charge or constant-potential schemes remain limited in their ability to accurately describe the physical electrode-electrolyte interface, as they can create artificial effects, such as inducing a dipole, shifting the target potential of the simulation, or requiring instantaneous relaxation of the interface. In this work, the effect of applying the fluctuation-dissipation theorem to the applied potential on reaction barriers in ab initio slow-growth molecular dynamics simulations is investigated. Three simulation schemes are compared: the NVT ensemble (constant charge), the µVT ensemble (constant potential), and NVTΦ, realized through FLEX++, a Python wrapper for VASPsol++ that controls the number of electrons at each simulation step according to the fluctuation-dissipation theorem. The reaction barrier of the Volmer step of the HER on Au(110)/water and Cu metal leaching from a CuN4HC single-atom catalyst during CO2RR are calculated as test cases. For the Volmer step, the reaction barrier increases with the applied potential for all ensembles, but each simulation repetition yields a considerably different barrier for the NVT and µVT ensembles, whereas NVTΦ yields a more consistent estimate. The reason is that FLEX++ maintains the electrode potential more consistently along the reaction coordinate, while letting the electrode potential vary to accommodate the reaction event. These differences in barrier height between the repetitions originate from the covalent bonds and H-bond network around the O donating the H in the Volmer step. For Cu metal leaching, NVTΦ shows an increased barrier of 0.1 eV, on average, over standard NVT. This decreased NVT barrier is rationalized by a lack of charge fluctuations that would otherwise destabilize the solvated leaching metal complex, if present.
Source: ChemRxiv
Institution: Technical University of Denmark
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funder: Novo Nordisk
Award: G8746932616
OpenAlex ID: W7213987720