▎ 摘　　要

In agreement with observation, local-density approximation (LDA) optimization of one- and two-layer clusters of Ir atoms, adsorbed periodically on a graphene/Ir(111) moireacute, shows that the two-layer clusters only become favorable energetically once the clusters comprise as many as 26 adatoms. Heretofore it was known that the LDA predicts smaller islands to grow flat. In showing that the LDA captures the transition to three dimensionality, the present results support its use broadly to analyze Ir island formation on the graphene-covered metal.