Enthalpy units – LAMMPS Beginners


I am dumping enthalpy using the thermo keywords with units real. I have read that the units of enthalpy is Kcal/mol but the value I get from the simulation does not match the value I have from the experiment. Only when I divide the lammps-reported enthalpy with the number of atoms in the system, these two agree. So I am confused. what is the real unit of enthalpy? is it Kcal*#atoms/mole?

This is not a question of units but of normalization.

Thanks, Axel, but do not we already normalize when we divide the energy by the total number of moles in the system?

Please see the thermo_modify documentation. Please also take note of the difference between intensive and extensive properties, and finally keep in mind that LAMMPS does not have any concept of molecules, it just looks at atoms and interactions between them.

Upon further consideration, it looks like you are misunderstanding what kcal/mol means:
it is the amount of energy that would be 1 kcal, if you have 1 mole of atoms (=6.02214076×10^{23}).

Besides, there are usually no moles in atomic simulations. :stuck_out_tongue_winking_eye:

I do understand what kcal/mole mean :wink: And yes, we have far less number of molecules than a mole contains in almost all MD simulations! Anyway, thanks very much for your explanations.

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