[lammps-users] About fix thermal/conductivity

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1

Hi there,

I am using command fix thermal/conductivity to compute the thermal conducitivity of carbon nanotube. However, I was unable to get the correct temperature profile after arriving at the steady state. Can anybody tell me what part I used was wrong? My guesssing is the problem occurs at fix ave/spatial part to output the temp profile. or can anybody give me your already checked code (as simple as it can) to let me learn? Thanks for your help.

units metal
dimension 3
boundary p p p
atom_style atomic
pair_style tersoff
read_data data.dat
pair_coeff * * SiC.tersoff C
mass 1 12

velocity all create 300 873586443 dist gaussian
fix 1 all nvt 300.0 300.0 0.5 drag 0.4

#output of varaibles
thermo_style custom step temp pe ke etotal pxx pyy pzz
thermo 1000
timestep 0.001
run 10000
unfix 1
fix 1 all nve
fix 2 all thermal/conductivity 100 z 40
compute ke all ke/atom
variable temp atom c_ke[]/1.5
fix 3 all ave/spatial 10000 1 100000 z lower 0.25 v_temp &
file tmp.profile units reduced
dump 1 all custom 100000 dump.* tag x y z
run 1000000

Best,

AC

2

Looks fine to me other than that you have only 4 spatial bins.
So not sure what kind of "profile" you expect to extract.
The fix thermal conductivity swaps KE between atoms
in the middle/bottom of the box, so that's really only
half the z height.

Steve

3

Hi Ajing,

1) if you use units "metal", it should be

variable temp atom c_ke[]/(1.5*8.67e-5)

2) fix 3 all ave/spatial 1 10000 100000 z lower 0.25 v_temp &

average results of 10000 iterations separated by 1 iteration every
100000 iterations

Best,
German

4

Hi steve,

Ideally, the temp profile should be linear since the heat source is placed at the lower part and the heat sink is located at the middle of CNT. But the profile I got is pretty flat (because the heat flux is so small?). I dont know what is going on.
Maybe need to read the source code to see what is the thing I need to care about.

Best,

AC