Specific heat in gmx energy

GROMACS version: 2021
GROMACS modification: Yes/No

Hello everyone,

I am trying to calculate the specific heat of CaCl2 solution by using gmx energy. I noticed that the unit of specific heat is J/(mol K). I am confused that what is the mol here? Does it refer to the mole of CaCl2 in the solution or the mole of the whole solution?

Thanks so much for your answer!

All references to “per mole” in GROMACS units refer to “per mole of equivalent systems.”

Thank you so much for the answer. In my simulation, I added Ca2+ and Cl- into a box with water. For example, if we have 1000 water molecules and 200 Ca2+ and 400 Cl-. Should I set the -nmol to 1600 (sum of water molecules and 2 ions) or 1200 (sum of water molecules and CaCl2 molecules)?

The -nmol flag is only relevant for pure systems in calculation of e.g. ΔHvap.

Thank you! If so, may I ask how can we calculate the specific heat for a mixture system?

I also used gmx dos and I noticed that in the dos.log file, the number of molecules is the sum of water molecules and 2 ions.