An inquiry about flexible scanning

[Kilmorph]

Hi Dr. Moussa,

As the title shows, I have a question regarding the flexible scanning using MOPAC: During each step, there would be a small part printing "VARIABLE" and "FUNCTION", however the value under "FUNCTION" seems to be heat of formation rather than total energy. Thus, I am wondering:

a) Will flexible scanning with MOPAC output total energies, or only the heats?

b) Can I use the difference of heats of each step to represent the relative energy of different conformations?

Thanks a lot in advance!

[godotalgorithm]

MOPAC is only set up to report the heats during its various scanning features. If you compile MOPAC yourself, then you can add any extra print statements you want with additional information that has been computed but not printed.

I generally do not recommend using the "total energy" reported by MOPAC as discussed in an Issue. Within MOPAC, it's a highly arbitrary quantity that wasn't directly fit to anything during the model fitting process. At MOPAC's level of modeling fidelity, heat differences between different conformations are intended to be used as a proxy for conformational energy differences.