I'm trying to review how to calculate bond dissociation energy for C-C in ethane, a very simple calculation (or should be).
I get the following Hartree energies for SCF 6-31G(p) for methane, ethane, and H2:
ch4_spe -40.194639920746,
ethane -79.228125042573,
h2 -1.126456057886,
I would think that to get the C-C bond dissociation energy, I would simply do (Perl code)
$energies{ethane} - $energies{ch4_spe} * 2 - $energies{h2}
correct?
The reason that I'm asking is that this give an answer of 2.2876 Hartree using NWChem, which converts to 6006 kJ/mol, which is off by about a factor of 17 from the correct value of about 346 kJ/mol. I know that SCF isn't that accurate, but it shouldn't be this far off. I optimized the bond lengths using Avogadro.
This is the correct method to calculate the C-C bond energy?