Predicted crystal structures of superhard sp³-hybridized carbon allotropes. Both structures in (a) and (b) consist of (4+6+8)-membered rings,^[30,72] and the carbon structure in (c) consists of (5+6+7)-membered rings.^[29] These structures were viewed as solutions to the experimentally mysterious cold-compressed graphite or carbon nanotubes.^[25,47,48] The carbon structures in (d) and (e) contain the unique C₆₀ and C₃₂ cages, respectively.^[73,74] Notably, the predicted fcc-C₃₂ (e) has the same structure with recently synthesized LaH₁₀ possessing T_c near room temperature at high pressure.^[75–77] (f) A type of microporous carbon form.^[78]