eV for sp 3 hybridization of carbon. The BEBOP hybridization energy contribution was estimated from the 2s gross orbital occupations and the energies of appropriate atomic states. The energy due to hybridization of molecular carbon is taken as the number of 2s electrons in a ground state carbon atom minus the number of molecular 2s electrons, multiplied by the 3 P→ 5 S atomic excitation energy (4.26 eV):