Dear lammps users：

I have some questions on ZnO thermal conductivity calculation，The fix heat/flux and fix thermal/conductivity command were selected to calculating the ZnO thermal conductivity.

1.fix heat/flux

I wrote the input file like the manual (http://lammps.sandia.gov/doc/compute_heat_flux.html), the average thermal conductivity of ZnO(Model: x 5.0nm y 4.8nm z 5.3nm) is about ~50W/mk. The thermal conductivity-m curve you can see the fig 1 in the attachment.

2.thermal/conductivity

The periodic boundary wurtzite-type ZnO was selected to calculating thermal conductivity in x y z direction 2.8nm 2.9nm 15.7nm respectively。The main command as following：

fix temp_profile all ave/spatial 1 100000 100000 z lower 1.0 v_temp file temp.profile units lattice #YL for test

fix heat_swap all thermal/conductivity 10 z 60

fix e_exchange all ave/time 10 1 100000 f_heat_swap file e_exchange.dat

fix accumu_thermalK_out all ave/time 10 1 100000 v_accumu_thermalK file thermal_conductivity.dat

I used this “variable accumu_thermalK equal f_e_exchange*{ev2J}/(2*0.001*{N}*{ps2s}*{Ox}*{Oy}*{An2m}*f_delta_out)*(${Oz}/60.0*26.0)” variable command to calculating it.

timestep 0.001

N step

Is it right（this variable to calculate the thermal conductivity）?

Temperature gradient is linear in the fig 2 (in the attachment). the average thermal conductivity is about 5W/mk.

Now, Two kinds of method to calculate the thermal conductivity of why have so big difference(The two methods with the same potential)?