# [lammps-users] Questions on fix thermal/conductivity command

I’ve seen the LAMMPS manual, posting Q/A of archive, and relavant paper for thermal conductivity calculation but the following is not clear to me. advices.

1. For J = kappa*E in Muller−Plathe method, I know that J will be predetermined and we only investigate E (gradient) to obtain kappa.

But it is really hard to know what is J in fix thermal/conductivity analysis.
Where the information on the value of flux J can be found in the output using fix thermal/conductivity command?

1. My result for temp.profile is as follows.

# Layer Coord Ncount v_temp

301000 20
1 -9.5 0 0
2 -8.5 0 0
3 -7.5 0 0
4 -6.5 0 0
5 -5.5 0 0
6 -4.5 0 0
7 -3.5 0 0
8 -2.5 0 0
9 -1.5 0 0
10 -0.5 486.39 294.463
11 0.5 473.61 305.993
12 1.5 0 0
13 2.5 0 0
14 3.5 0 0
15 4.5 0 0
16 5.5 0 0
17 6.5 0 0
18 7.5 0 0
19 8.5 0 0
20 9.5 0 0

What does Ncount (e.g., 486.39) mean here?
I suppose that v_temp should be average temperature value. Is it right?

I think that zero values in 1-9 bins and 12-20 bins should be non-zero if we obtain meaningful temperature profile.
What’s wrong with my input description(fix commands)?

I use the following commands.

fix 3 all ave/spatial 10 100 1000 z lower 1. v_temp file tmp.profile units box
fix flux all thermal/conductivity 50 z 24

Should I increase N of 50 (= perform kinetic energy exchange every N steps) in fix thermal/conductivity command?

Cheers,

Luke

You can output the flux using thermo_style command. Read the doc file for this command on how to output the values which are calculated by various fixes

The problem (most probably) with your system is that your system is elongated either along X and Y direction and you are binning along Z direction. If number of atoms are coming out to be zero, there is some problem on how you are binning the system