Dear Lammps users,

Hi, I am learning thermal conductivity calculation using Green-Kubo approach.

As an exercise, I tried calculations for silicon and graphene, and both have worked well.

I am also trying to calculate thermal conductivity of copper, but I got only 15 ~ 20 W/mK

for the thermal conductivity of copper (which is supposed to be around 350 W/mK).

I tried a few different potentials (meam, eam, and eam/alloy) and different sizes of structure,

but they all have produced the similar results. I am sure that my unit conversion is correct

as other materials proved.

I am copying my input file below which is not much different from the example given by Lammps.

Please let me know if you can find any errors from my input.

Thanks in advance,

# settings

variable T equal 300

variable V equal vol

variable dt equal 0.001

variable kB equal 1.3806504e-23 # [J/K] Boltzmann

variable eV2J equal 1.602e-19

variable A2m equal 1.0e-10

variable ps2s equal 1.0e-12

variable convert equal {eV2J}*{eV2J}/{ps2s}/{A2m}

variable alat equal 2.456

variable p equal 10000 # correlation length

variable s equal 10 # sample interval

variable d equal $p*$s # dump interval

# setup problem

units metal

boundary p p p

atom_style atomic

lattice fcc 3.610 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1

region box block 0 4 0 4 0 4 units lattice

create_box 1 box

create_atoms 1 region box

replicate 2 2 2

mass 1 63.546

velocity all create $T 4928459 mom yes rot yes dist gaussian

pair_style eam

pair_coeff * * Cu_u3.eam

neighbor 2.0 bin

neigh_modify delay 10

timestep ${dt}

dump 1 all cfg 100000 dump.config.*.cfg mass type xs ys zs vx vy vz x y z

# 1st equilibration run

fix 1 all nvt temp $T $T 0.5

thermo 100000

run 1000000

velocity all scale $T

unfix 1

undump 1

# thermal conductivity calculation

reset_timestep 0

compute myKE all ke/atom

compute myPE all pe/atom

compute myStress all stress/atom virial

compute flux all heat/flux myKE myPE myStress

variable Jx equal c_flux[1]/vol

variable Jy equal c_flux[2]/vol

variable Jz equal c_flux[3]/vol

dump 2 all cfg $d dump.config.*.cfg mass type xs ys zs vx vy vz x y z
fix 1 all nve
fix JJ all ave/correlate $s $p d &
c_flux[1] c_flux[2] c_flux[3] type auto &
file profile.heatflux ave running
variable scale equal {convert}/${kB}*s*{dt}/$T/T/vol
variable k11 equal trap(f_JJ[3])*{scale}

variable k22 equal trap(f_JJ[4])*{scale} variable k33 equal trap(f_JJ[5])*{scale}

thermo $d

thermo_style custom step temp v_Jx v_Jy v_Jz v_k11 v_k22 v_k33

run 2000000

variable kappa equal (v_k11+v_k22+v_k33)/3.0

print “running average conductivity: ${kappa}”