‘C8 phase’: Supercubane, tetrahedral, BC‐8 or carbon sodalite?

Abstract

AbstractWith the use of ab initio density‐functional theory (DFT) and electron diffraction calculations, the crystal structures of a carbon ‘C8 phase’ are found. Total energies and electron diffraction patterns are calculated for all possible known to date candidates, namely supercubane, tetrahedral, BC‐8 and sodalite (SOD) structures as nearest neighbours in unit cell size. The results of calculation agree well with only one phase. The structure can be attributed to sp3‐hybridized carbon SOD zeolite with 12 atoms in a unit cell. Carbon sodalite belongs to space group no. 229, with a unit cell of a = 4.34 Å, and a calculated crystal density of 2.927 g/cm3. The existence of a tetrahedral phase (a = 3.86 Å) is discussed. A simple formula of relative structural stability is proposed for all sp3‐hybridized phases with unit cells of 3.5–5.0 Å.magnified image