Density functional theory (DFT) calculations of charged surfaces and molecules are essential for advancing electrocatalysis and energy materials, yet they are traditionally hindered by the requirement of charge neutrality under three-dimensional (3D) periodic boundary conditions. To overcome this limitation, we introduce a recent methodological advancement in the Vienna ab initio simulation package (VASP) that enables 0D and 2D open boundary conditions. By utilizing a Coulomb kernel truncation method combined with a highly efficient padding approach, we systematically eliminate unphysical long-range vacuum interactions and selectively subtract unwanted periodic artifacts. The computational efficiency and robustness of this approach are demonstrated through large supercell calculations of a charged chlorine defect on an NaCl(001) surface and extensive molecular dynamics simulations of a stepped Au(211) water electrode-electrolyte interface.

Building on these methodological foundations, this work investigates the free solvation energies of sodium and fluorine ions at an unreconstructed Au(111)-water interface. Both charged and uncharged slabs are considered. To achieve the necessary timescales, we employ on-the-fly machine learning force field (MLFF) training in VASP, utilizing large supercells containing approximately 100 water molecules. These force fields are subsequently refitted using GRACE-2layer models.

Leveraging these accelerated models, we perform extensive thermodynamic free energy simulations using the weighted histogram analysis method (WHAM) and metadynamics to extract accurate free energy profiles.

Crucially, we address the fundamental challenge of simulating ions close to an electrode at the point of zero charge using finite slab models.

Our simulations demonstrate that periodic slab calculations for ions dissolved in water must be performed in charged states to correctly capture the macroscopic, infinite point-of-zero-charge limit.