2. For each ruthenium atom in the structure, change it to nickel with probability x (where x is the nickel concentration). The number of nickel atoms introduced to the structure this way is the number of initially placed clustering seeds N init 3. Calculate the allowed number of seeds in the structure, N allowed . With the size of the clusters (in this case 3), the nickel concentration x and the total number of metal atoms in the structure N , this is given as N allowed = N •x 3 (rounded to the nearest integer).