Yao et al. attempted revealing thermodynamic stable polymorphs of BC 5 from structural searches combined with first-principles structural optimizations . Besides of tetragonal (I4m2) polymorph, trigonal (P3m1) and triclinic (P-1) forms of BC 5 were theoretically predicted. The study revealed mixed stacking of covalent C-C and metallic B-C substructures with an overall metallic system keeping ultra-hard mechanical properties.