Global structural optimization of Si magic clusters on the Si(1 1 1) 7 × 7 surface

We performed global structural optimization using a genetic algorithm in combination with tight-binding and first-principles calculations to study the structures of the magic clusters on the Si(1 1 1) 7 × 7 surface. Our calculations show that the magic cluster observed in scanning tunneling microscopy (STM) experiment [I.S. Hwang, M.S. Ho, T.T. Tsong, Phys. Rev. Lett. 83 (1999) 120] consists of eight Si atoms on the faulted half of the Si(1 1 1) 7 × 7 surface. Simulated STM images of our Si magic cluster exhibit a ring-like feature similar to STM experiments.