Structural competition in boron group elements has been studied by means of ab initio calculations. For boron we predict a structural change $\alpha \mathrm{\text{−}}\mathrm{B}\to \alpha \mathrm{\text{−}}\mathrm{G}\mathrm{a}$ accompanied by a nonmetal-metal transition at a pressure of about 74 GPa. For Al and Ga we find an icosahedron based elemental modification ($\alpha \mathrm{\text{−}}\mathrm{B}$) 0.22 and $0.05\mathrm{e}\mathrm{V}/\mathrm{\text{atom}}$, respectively, higher in energy than the corresponding metallic ground state structures. In particular, the low energy difference for Ga raises expectations into the experimental feasibility of new modifications for these elements, especially in nanosized systems.

• Received 23 May 2002

DOI:https://doi.org/10.1103/PhysRevLett.90.065701