where 𝐸 𝑠𝑙𝑎𝑏 2𝐶𝑢 is the DFT calculated energy of a substrate with 2 Cu atoms and 𝐸 𝑎𝑑𝑠 𝑙𝑜𝑤𝜃 is the adsorption energy of Cu at low coverage. Thus, the interaction energy can be obtained by direct measurement of the binding energy of two Cu adatoms on a given substrate, as shown in the right part of Figure . Since there are different directions of the interaction, the mean and standard deviations of the interaction energy are calculated as shown in the bottom plot of Figure . The mean interaction energy of Cu adatoms on bare graphene substrate is ~2.17 and Cu atom, and the interaction energy between two adjacent Cu atoms on different substrates.