# thermal conductivity of Silicon

Dear Users,
I am new user of LAMMPS. I was trying to get thermal conductivity of silicon(10X10X10) at room temperature (300K).The result I have got is 0.1832749825[W/mK].
whereas the experimental value at room temperature is around 150[W/mK]
I am giving bellow the script file and the output file. Please suggest me about that discrepancy.

Thanks & Regards

INPUT FILE

# Sample LAMMPS input script for thermal conductivity of solid Ar

units real
log log.thermo
variable T equal 300
variable V equal vol
variable dt equal 1.0
variable p equal 2000 # correlation length
variable s equal 1 # sample interval
variable d equal \$p*\$s # dump interval

# convert from LAMMPS real units to SI

variable kB equal 1.3806504e-23 # [J/K] Boltzmann
variable kCal2J equal 4186.0/6.02214e23
variable A2m equal 1.0e-10
variable fs2s equal 1.0e-15
variable convert equal {kCal2J}*{kCal2J}/{fs2s}/{A2m}

# setup problem

dimension 3
boundary p p p
lattice diamond 5.431020504 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
region box block 0 10 0 10 0 10
create_box 1 box
create_atoms 1 box
mass 1 28.0855
pair_style sw
pair_coeff * * Si.sw Si
timestep \${dt}
thermo \$d

# equilibration and thermalization

velocity all create \$T 102486 mom yes rot yes dist gaussian
fix NVT all nvt temp \$T \$T 10 drag 0.2
run 8000

# thermal conductivity calculation, switch to NVE if desired

#unfix NVT
#fix NVE all nve
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
fix JJ all ave/correlate \$s \$p d & c_flux[1] c_flux[2] c_flux[3] type auto file J0Jt.dat ave running variable scale equal {convert}/\${kB}/\$T/\$T/\$V*s*{dt}
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_style custom step temp v_Jx v_Jy v_Jz v_k11 v_k22 v_k33
run 100000
variable k equal (v_k11+v_k22+v_k33)/3.0
variable ndens equal count(all)/vol
print “average conductivity: \$k[W/mK] @ T K, {ndens} /A^3”

OUTPUT FILE

LAMMPS (12 Jun 2011)
Lattice spacing in x,y,z = 5.43102 5.43102 5.43102
Created orthogonal box = (0 0 0) to (54.3102 54.3102 54.3102)
1 by 1 by 1 processor grid
LAMMPS (12 Jun 2011)
Created 8000 atoms
LAMMPS (12 Jun 2011)
LAMMPS (12 Jun 2011)
Setting up run …
Memory usage per processor = 3.88605 Mbytes
Step Temp E_pair E_mol TotEng Press
0 300 -34692.8 0 -27539.75 2039.4771
2000 298.54018 -25587.308 0 -18469.065 3881.0011
4000 297.88202 -25422.241 0 -18319.691 4330.0133
6000 298.48454 -25463.276 0 -18346.36 4251.9003
8000 303.52777 -25504.876 0 -18267.711 4351.6948
Loop time of 1083.56 on 1 procs for 8000 steps with 8000 atoms

Pair time () = 1076.47 (99.3454) Neigh time () = 2.71907 (0.250938)
Comm time () = 0.778279 (0.0718259) Outpt time () = 0.000267029 (2.46436e-05)
Other time (%) = 3.59513 (0.331787)

Nlocal: 8000 ave 8000 max 8000 min
Histogram: 1 0 0 0 0 0 0 0 0 0
Nghost: 6310 ave 6310 max 6310 min
Histogram: 1 0 0 0 0 0 0 0 0 0
Neighs: 0 ave 0 max 0 min
Histogram: 1 0 0 0 0 0 0 0 0 0
FullNghs: 314634 ave 314634 max 314634 min
Histogram: 1 0 0 0 0 0 0 0 0 0

Total # of neighbors = 314634
Ave neighs/atom = 39.3293
Neighbor list builds = 107
Dangerous builds = 0
Setting up run …
Memory usage per processor = 6.55825 Mbytes
Step Temp Jx Jy Jz k11 k22 k33
0 303.52777 2.5531227e-06 4.007608e-06 1.5116147e-06 0.00020301505 0.0005002134 7.1165101e-05
2000 296.0052 1.6294656e-07 8.4757968e-06 -1.3778724e-05 1.9181163 0.32243902 -0.16272834
4000 299.77155 -2.6721054e-06 -8.1760149e-06 -8.6290394e-06 0.6376134 0.0068575213 0.08948722
6000 297.37444 -2.4663349e-06 2.2979218e-06 8.0432749e-06 0.42809529 -0.10018507 0.11123582
8000 298.65918 7.0964745e-07 -2.3130065e-06 -7.7538574e-06 0.35707644 0.043425438 0.077682706
10000 303.08376 -5.0099107e-06 3.3658571e-06 -2.1141601e-06 0.23664915 0.28220569 0.095267134

:
:
:

96000 300.30057 8.0176056e-06 2.7098316e-06 -6.8740613e-06 0.20315033 0.22886874 0.12066023
98000 294.86472 8.4298057e-06 1.3330126e-06 4.315606e-06 0.20746175 0.22187796 0.12377436
100000 301.67178 1.492394e-05 8.880098e-06 -1.303326e-06 0.20294253 0.22140104 0.12548137
Loop time of 16198.2 on 1 procs for 100000 steps with 8000 atoms

Pair time () = 16022.6 (98.916) Neigh time () = 34.0301 (0.210086)
Comm time () = 10.1111 (0.0624215) Outpt time () = 0.0465102 (0.000287133)
Other time (%) = 131.394 (0.811167)

Nlocal: 8000 ave 8000 max 8000 min
Histogram: 1 0 0 0 0 0 0 0 0 0
Nghost: 6254 ave 6254 max 6254 min
Histogram: 1 0 0 0 0 0 0 0 0 0
Neighs: 0 ave 0 max 0 min
Histogram: 1 0 0 0 0 0 0 0 0 0
FullNghs: 314110 ave 314110 max 314110 min
Histogram: 1 0 0 0 0 0 0 0 0 0

Total # of neighbors = 314110
Ave neighs/atom = 39.2638
Neighbor list builds = 1340
Dangerous builds = 0
average conductivity: 0.1832749825[W/mK] @ 300 K, 0.04993966903 /A^3

You're using real units, and the SW potential
files provided with LAMMPS are in metal
unts (see the SW doc page). Nothing about
your simulation will be correct in that case.

Steve