The authors performed first-principles calculations to investigate the effect of the strain on the hexagonal motifs formed on the Ir(100) surface overlayer with (5 x 1), (8 x 1), (12 x 1), and (14 x 1) periodicities. Their calculations showed that the unstrained (5 x 1) phase is the most stable phase, which is consistent with previous theoretical calculations and experimental findings. Further analysis on the surface energy versus strain suggests the occurrence of the strain induced phase transition among various hexagonal reconstructions. Such a phenomenon can be further qualitatively elucidated by analyzing the computed average standard deviation of angles between the three adjacent atoms of the hexagonal top layer. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3497027]