Comparative study of atomic and electronic structures of P and Bi nanofilms

We perform first-principles calculations on P and Bi nanofilms and clarify the atomic and electronic structures of these films. The energy gap of the two-atomic-layer film of P has a band gap of 1.2 eV, and as the thickness becomes large, the band gap becomes close to that of the bulk, which is a semiconductor. The most stable structure of the two-atomic-layer Bi film has an energy gap of 0.2 eV and two atoms on the surface are buckled. The nonbuckled structure is metallic and is metastable and its energy is slightly (12 meV) higher than that of the buckled structure. We discuss why the P films are nonbucked and the stable Bi films are buckled.