Modeling Solid-Liquid Interfaces Using Next Generation Quantum Molecular Dynamics

Fuel cells provide electric current based on oxidation and reduction, and the cathode's oxygen reduction reaction can be catalyzed at the solid-liquid interface of a metal-nitrogen doped graphene sheet and water. However, the precise electron transfers and molecular roles are unknown. While ab-initio density functional theory provides ground state electronic properties and reaction energetics, quantum molecular dynamics can reveal important time-dependent ensemble properties. Initial relaxation of the system's charge distribution is carried out through the density functional tight binding approach, and the required relaxation iterations and computing times are compared for different atomic charge update schemes. With the system starting in equilibrium, the nuclear and electronic degrees of freedom are updated using the extended Lagrangian Born-Oppenheimer MD formulation, and the total system energy is tracked to ensure conservation. Characteristic peaks in system energy, temperature, and charge distribution describe the possible occurrence of a reaction when the oxygen molecule breaks into anion radicals.