Structural, mechanical, and electronic properties of Rh(2)B and RhB(2): first-principles calculations

The crystal structures of Rh(2)B and RhB(2) at ambient pressure were explored by using the evolutionary methodology. A monoclinic P2(1)/m structure of Rh(2)B was predicted and donated as Rh(2)B-I, which is energetically much superior to the previously experimentally proposed Pnma structure. At the pressure of about 39 GPa, the P2(1)/m phase of Rh(2)B transforms to the C2/m phases. For RhB(2), a new monoclinic P2(1)/m phase was predicted, named as RhB(2)-II, it has the same structure type with Rh(2)B. Rh(2)B-I and RhB(2)-II are both mechanically and dynamically stable. They are potential low compressible materials. The analysis of electronic density of states and chemical bonding indicates that the formation of strong and directional covalent B-B and Rh-B bonds in these compounds contribute greatly to their stabilities and high incompressibility.