ure ). The potential energy curves for polyvalent species such as carbon present a greater challenge. Rather than increase the complexity of the BEBOP model, we have elected to compromise and select a value for the exponent, ζ CC , that reproduces the energies of ethane, ethylene, and acetylene, at their equilibrium geometries, R e (Figure ). Because the BEBOP model cannot explicitly calculate zero-point vibrational energies (ZPVE), we have employed the ROCBS-QB3 BDE value that includes ZPVE (i.e., D 0 ). Figure : The BEBOP potential energy curves for ethane, ethylene, and acetylene.