Structure and stability of Mg-intercalated boron nanotubes and crystalline bundles.

First principles calculations based on density functional theory predict a highly selective adsorption site for Mg atoms and negligible preference for the growth of Mg islands on the tubular surface of Mg-intercalated (small diameter) boron nanotubes, thereby establishing the criterion for understanding the growth mechanism of single-walled boron nanotubes (SWBNTs) supported by magnesium. On the other hand, the Mg–SWBNT bundles can be considered as an ‘electrostatic’ bound system consisting of partially ionized Mg and partially ionized tubules. The metallic character of the tubular Mg–B bundles is then attributed to boron atoms forming a metallic wire, while the role of Mg atoms is limited in enhancing the stability of the crystalline bundles.