# [lammps-users] question about compute heat/flux

Dear Bo,

Im not in a position to answer:
"Why the electrostatic contribution is still omitted?"
Maybe further testing/discussions on the implementation are pending..

Except electrostatics, other components of the potential are already
included in the current version.
Also, since LAMMPS versions have changed since the time German posted
his files, im not sure
if replacing the existing files with files German provided will work.
He would be the best person to answer this.

Best,
Mario

PS: Plz keep the mailing list in Cc.

Im not in a position to answer:
"Why the electrostatic contribution is still omitted?"
Maybe further testing/discussions on the implementation are pending.

The answer is simple. Most people don't run Ewald, they run PPPM,
which can be an order of magnitude or more faster.

So having per-atom energy (used by heat-flux) in Ewald, is not sufficient.
And we don't know how to do it for PPPM.

Steve

It will not work with current version of heat flux
German

Dear all,

I has two gold walls with different temperature, and water inside. I need to calculate heat flux of my system. So I want to know when the electrostatic contribution is omitted, how much will it affect to the value of my heat flux?

Thank you!

ziyuan

Ziyuan,
The Green Kubo method is generally used for homogeneous systems. So, I will be very catious when using it to study graphene water interface. About the electrostatic contribution, it should be negligible given significant charges on water molecules.

Best
Vikas

Thank you Vikas. So if I used fix heat, I don’t need to calculate heat flux. And my two walls will become stable with a specific higher and colder temperature. So how fix_heat relates heat flux with temperature here?

ziyuan

Sorry, I wanted to say it should not be negligible.

Relation: The higher the parameter you provide as eflux in fix heat, the higher will be the temperature different between the two walls after reaching steady state.

Thank you. I understand this. I mean which kind of mechanism of fix heat here? If I maintain temperature, then using Green-kubo to calculate heat flux. But I don’t know how fix heat works to get the stable temperature gradient?