Dear Users

I am using the Green-Kubo approach to calculate thermal conductivity of nanowires. In most published works the range of simulation time is 6-18ns but mine is not converging even after 30ns and the values remained very large !. I tried to use different time steps (timestep=0.1,0.3,0.5,0.8 fs) and correlation time (100,300,500,800ps) but no change. The potential model I am using gives appropriate values of lattice and elastic constants and I also checked the structure of the nanowires is maintained with the minimum total energy after equilibration steps. I think I did some thing wrong in the G-K calculations ! Suggestion or ideas are of great help !!! Below is an extract from the input file.

…

…

…

dimension 3

boundary f f p # periodic BCs along the axis of the nanowire

read_data a.dat

…

…

…

# equilibration and thermalization

velocity all create $T 1026 mom yes rot yes dist gaussian

fix NVT all nvt temp 300 300 1 drag 0.2

run 1000000

# thermal conductivity calculation, switch to NVE if desired

unfix NVT

fix NVE all nve

run 1000000

reset_timestep 0

compute myKE all ke/atom

compute myPE all pe/atom

compute myStress all stress/atom NULL virial

compute flux all heat/flux myKE myPE myStress

variable Jz equal c_flux[3]/vol # the flux along the z-axis of the nanowire

fix JJ all ave/correlate $s $p $d &

c_flux[3] type auto file J0Jt.dat ave running # The correlation for the flux along the z-axis

variable scale equal {convert}/{kB}/$T/$T/$V*s*{dt}

variable k33 equal trap(f_JJ[3])*${scale}

thermo_style custom step temp v_Jz v_k33

run 30000000

variable k equal v_k33

variable ndens equal count(all)/vol

print “average conductivity: $k[W/mK] @ T K, {ndens} /A^3”

Regards,

MIchel