Basin hopping (BH) is a global optimization approach combining local energy minimization and a Monte Carlo sampling method, where local minimization is introduced after each random perturbation. In other words, rather than single-point energy evaluation, the objective function is the locally minimized energy given by Ẽ(x) = min[E(x)], meaning that the energy associated with each point in configuration space, x, is the energy of the local minimum that is reached upon energy minimization from that point: min[E(x)]. Thus, the acceptance probability of perturbing structure a to b is calculated by