Thermal conductivity of fluid LJ muller plathe method

LAMMPS LAMMPS Beginners
1

Hello all
I have two question about thermal conductivity :

  1. for kappa computing : how to compute or extract or get the cumulative delta energy for example in the script in.mp
    here is what is written in ReadMe to explain how to get the value of kappa.
    in.mp : dQ = 15087 / 100 / 18.82^2 / 2
    15087 = cumulative delta energy, tallied by fix thermal/conductivity
    100 = 20,000 steps at 0.005 tau timestep = run time in tau
    xy box area = 18.82^2
    divide by 2 since energy flux goes in 2 directions due to periodic z
    dTemp = 1.16 from log file for average Temp difference between 2 regions
    dZ = 18.82
    Kappa = 3.45

  2. could we compute directly kappa within the script with this method like th gk method ?

thanks in advance

2

Please see the documentation of the fix thermal/conductivity command — LAMMPS documentation
and 8.3.1. Output from LAMMPS (thermo, dumps, computes, fixes, variables) — LAMMPS documentation

Probably yes, if you can figure out how to write a suitable equal style variable that combines the various properties and pre-processed values.

3

Thank you dear Mr Kohlmey,
i visited the link about output from lammps (thermo_style command) and saw ecouple !! is this how to get the cumulative delta energy ? otherwise I tried it but the code crash (error unknown key word ecouple)

I woder how to get 15087 in the example in the script in.mp
dQ = 15087 / 100 / 18.82^2 / 2

could you give me more detail please ?
thanks a lot

respectfully,

4

Emphatically no.

You get it from the fix. That is what the readme says and that is why I pointed you to the fix documentation. If you don’t understand what that means or how to do it, you need to spend more time on learning more LAMMPS basics and how fixes work and how you extract information from them.

All you need to know is explained in the LAMMPS manual, but I don’t have the time to spoon feed it to you.