A Novel Approach for First-principles Calculations of Charged Adsorbates in Periodic Metallic Systems

Charged species are often found in various chemical processes such as catalysis, electrochemistry and acid–base reactions. DFT studies are always used to gain an in-depth understanding of these reactions. However, in periodic metallic systems, the presence of charge in supercells faces serious convergence problems, and a new method is needed to calculate charged slabs to study the reactions involving charged species.

To study the heterogeneous catalysis reactions, a simple method is proposed for the calculations of charged adsorbents. The DFT calculations are performed using the VASP package. The VASPsol solvation model and Grimmie dispersion corrections are considered in all calculations. The transition state for each reaction is located using the climb-NEB method. The zero point vibrations (ZPE) are obtained using the harmonic oscillator approximation to confirm the ground state and transition state geometries.

In the proposed new approach, a counter ion is placed at a non-interactive distance in the supercell, in an aqueous medium, to maintain the neutral behaviour of the systems while the adsorbents are charged. The charged species are confirmed using the Bader charged analysis. The method is used to study the adsorption of monovalent anions such as halides, hydroxides and H^- and bivalent anions such as Se^2- and SO₄^2-. The method is later used to study the detailed mechanism of BH₄^- hydrolysis on Ag⁰ and Au⁰ surfaces, and the obtained conclusions are validated with experiments. This approach offers a valuable method for studying the charged species in the catalytic process.