Although it has been touched on previously in the mailing lists, I 
think we need to clarify what OBMol::_energy contains. It is accessed 
in OBMol::SetEnergy(double) and by OBMol::GetEnergy().

Note that OBMol::GetEnergy(int) is separate, and is concerned with 
relative of conformer energies. Its data is kept in OBConformerData.

Can we agree that OBMol::_energy is the QM zero-point energy in 
kcal/mole? (I take this to be the energy released on assembling the 
molecule from elementary particles, but I may be wrong on this. 
However it is a large negative number.)

This arose because in gaussformat it was also being used for something 
else (now commented out with Dave Lonie's agreement pending 
resolution). It is also accessed in:
adfformat.cpp, cccformat.cpp, gamessformat.cpp, gulpformat.cpp, 
mopacformat.cpp, mol2format.cpp, pwscfformat.cpp, vaspformat.cpp,
and (reading only) mmodformat.cpp, xyzformat.cpp, cmlformat.cpp

Apart from the last (which I wrote), can those closer to these formats 
confirm that the proposal above would be consistent with them?

The comment in the declaration (and the API documentation) for 
OBMol::GetEnergy()) is
"return the heat of formation for this molecule (in kcal/mol)"
I understand something different by heat of formation (thermodynamics, 
defined to be zero for elements). Is "QM zero-point energy" the right 
expression?

Chris

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