in a clique (i.e., clique size, or the number of unchanged bonds), which should be maximized. In turn, the second term penalizes the situation that the selected vertices do not form a clique; it takes a positive value if and only if nonadjacent vertices v and u (i.e., (u, v) ∈ E G ) are selected, which contradicts the definition of cliques. The constant parameter A(> 1) controls the magnitude of the penalty term. In general, if the penalty strength is too large, the performance of SA will deteriorate; thus we set A to two, a moderate value greater than one, in this study. Because a QUBO problem is mathematically equivalent to an Ising model problem through the relation x i = (1 -σ i )/2, we can solve the maximum clique problem by Ising computing.