[lammps-users] question regarding fix heat

dear lammps users,

to calculate the thermal conductivity using the fix heat command.how do we measure the heat flux added??.the scalar value computed by this fix is a scaling factor of velocities.i would like to know how this quantity can be used to compute the heat flux.thanks in advance


Hello Vishnu,

With fix_heat, you dont need to mind about velocities, with eflux -parameter you adjust how many energy-units you will pump into system. It is per atom, so you will multiply it with number of atoms and calculate time how long it has been going. What you want to determine is how much energy has passed trough your system in simulation time. Then one one must apply fourier law properly to get conductivity. Ive got proper results with this compared to Muller-Plathe and bulk quantities, but it took couple of times to get it right.

If you need total coverage, proper read might be:

Patrick K. Schelling, Simon R. Phillpot and Pavel Keblinski, Comparison of atomic-level simulation methods for computing thermal conductivity, Physical Review B, Vol. 65. 144306, 2002.


Hello Tuomo,

Is the eflux parameter per atom or per group of atoms?
I've just received answer that it's per all atoms in the group
(see conversation "fix heat command")
If it's so the eflux should not be multiplyed by amount of atoms in the group.
Is it wrong?

Thank you.
German Samolyuk
2009/7/20 Tuomo Hyvönen <[email protected]>:


Im sorry, i always open my mouth before thinking trough, which is very bad. I hope it didnt cause problems for Vishnu. Its some time when i did it and i calculated per atom energies for myself to get idea of scales.

Tuomo Hyvönen

2009/7/23 German Samolyuk <[email protected]…33…24…>