How to calculate specific heat at constant pressure

LAMMPS
1

Dear LAMMPS users and developers,

I want to obtain the specific heat by calculating dH/dT under NPT ensemble.
I do not know how to calculate dH/dT in a proper way. I try to use finite difference to approximate derivative. However, I got a negative value no matter the difference formulas used including forward, backward and central difference.
I convert eV to J/mol as: enthalpy(in eV)*1.602176634e-19/(natoms/6.02214076e23)
The H-T and dH/dT-T relation in my simulation have been uploaded. The simulation temperature is 2000K. Could someone please give me some suggestions? Thanks for any help one can give.
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2

Sorry, but you have put your question into the wrong category.
This is not a question about LAMMPS but rather about MD methodology and statistical thermodynamics. I don’t even want to get into the question how applicable classical MD parameterizations studying properties over such a wide temperature range are and other issues related to the details of your simulation (system size, averaging, equilibration, convergence etc.).

You should try a different category here (e.g. science-talk) or a forum like physics-exchange.