I would like to make sure that my understanding of internal energy is correct. I'm not a thermodynamicist, so apologies in advance for what is probably a basic question.
I previously calculated density for a liquid system via molecular dynamics (NPT ensemble). I needed the results for use in fluid flow simulations. The calculations also generated internal energy, which I have so far ignored. However, someone has expressed interest in comparing my internal energy results with his. He looked at the same system, but used a different calculation method.
His internal energies, E, for all temperatures and pressures are between -11000 to -12000 kJ/mol. Mine are between -38000 and -40000 kJ/mol.
Here's my question. Is it correct that I don't need to worry that one of us has made a mistake--that it's OK for the absolute values to differ as long as the differences are consistent? For example, his highest-temperature, highest-pressure data point differs from his lowest-temperature, lowest-pressure data point by about the same amount as mine does.