= surface/volume), see Figure . pH and electric potential were introduced through the Computational Hydrogen Electrode . The O-deficient configurations were simulated by the sequential removal of O atoms. For each step, the same number of oxygen (1/48 of the total number of oxygen in the perfect slab) were random chosen and removed from the previous structure until all oxygen atoms were removed after 48 steps. The thermodynamic minima were identified for each case by using a NN-MD annealing simulation.