Boron and MgB 2 analogs of fullerenes and carbon nanotubes: A density functional theory study

Abstract

The structural analogy between fullerene and fragments of elemental boron allotropes extends to the structure of MgB 2, the simplest bulk high T c (39 K) superconductor, and graphite. Electronic structure studies on equivalent structures in the boron regime relate the chemistry of carbon and boron. The fullerene and nanotube analogs, B 84H 50, Mg 36B 60, Mg 30B 60, Mg 32B 60 and (6,6) boron and MgB 2 nanotubes were studied using first principles DFT calculations. Structures with all Mg atoms outside the B 60 cage are more stable than the structures with Mg atoms inside. The energy difference between MgB 2 sheet and nanotubes is close to that between graphite and carbon nanotubes. The α-boron allotrope is calculated to be about 2.4 eV lower in energy than the boron nanotube. Analysis of band structures indicates that boron and MgB 2 nanotubes are metallic.