Diffusion of Cu hexamer islands on Cu(111) and Ag(111) is studied using a molecular dynamics simulation technique with many-body potentials obtained from the embedded atom method.Simulations are carried out at temperatures 300,500 and 700 K,showing that shape-changing multiple-atom processes are more helpful for the diffusion rather than concerted motion of islands.Arrhenius plots of the diffusion coefficients provide effective energy barrier values of 161.29 ± 5 meV for Cu(111) and 179.34 ± 5 meV for Ag(111) surfaces.At 700K,one pop-up atom among island atoms is observed with correlative changes in the position and shape of the lower-layer adatoms.