Potential not only governs the direction of electrochemical reactions, but also shapes the electronic properties of single-atom catalysts dramatically. However, it is a challenge to simulate the potential effects on the theory side. Normally, DFT calculations were performed at a constant number of electrons, not constant voltage. In this work, we apply a new fixed-potential method (grand canonical method) in the DFT simulation to mimic the electrochemical processes, in which the total number of the electron in the system was floated to match the ‘‘applied voltage’’, or the electrode Fermi energy at the atomic level.