Fit energy

Hello Julian,

I’m sorry to bother you. In the process of fitting potential energy functions, if we are fitting based on experimental values, the energy values obtained from different simulation software can vary, and even differ by several orders of magnitude. Should we only fit the energy differences for the fitting to be correct? Additionally, regarding the use of the ‘reaction’ command, I have reviewed the help documentation but I’m still not quite clear on it. Is there a complete input file example that uses the ‘reaction’ command for fitting energy differences? Thank you for your help.


Hi LiMa,
If you’re using the same potential functions then different software should give the same values for the energy. The one exception might be for things like a Morse potential where things can be shifted by D0 in some cases and not in others.
For the reaction command, here is an example of how it might look:

2 -0.930000 100000.000000 1 -2.000 2 1.000

The numbers on the line mean the following:
2 => there are 2 reactants / products
-0.93 => the energy for the reaction in eV
100000.0000000 => the weight for the observable
1 -2.0 => configuration 1 in the input has it’s energy multiplied by -2.0, which means there are 2 formula units of it and minus means it’s a reactant
2 1.0 => configuration 2 is a product (1.0 is positive) and there is 1 formula unit.
In other words this is a dimerisation reaction of structure 1 that forms a dimer, structure 2.
Hope that helps.