# heat/flux command units

Dear LAMMPS user

I am doing a heat conduction between two parallel walls separated by argon gas. I am measuring the heat flux through the gas by the use of “compute heat/flux command” in real units.

``````According to the LAMMPS user guide, the final flux is in the units of energy/area/time.

As you know, the energy in real units is based on the Kcal/mole. the question is that how can I convert that to Joule?

Actually the Kcal/mole means the energy for one mole of the gas but the Joule doesn't consider the number of mole of the gas. So that really confused me how to convert that.

I am really pleased if any body could help me about that

Best Regards,
Reza

``````

for the purpose of these kinds of energy conversions, you need to
consider the entire system as one molecule.

axel.

The "mole" in “*kcal/mole*” means that energy (heat current or kinetic
energy …) is divided by Avogadro's number! As the values of energies in MD
simulations are very small, it is more convenient to use a very small unit
of energy (compared to *kcal* or *J*). "*kcal/mole" is *a convenient one*:*

*1kcal=4184J**⇒*

*1kcal/mole=4184/(6.022×10^23 ) J**⇒*

*1kcal/mole=6.948×10^(-21) J*

To test the units, you can calculate the total kinetic energy of your
system as follow: