Dear all:
In the manual, there is an example LAMMPS input script for solid Ar-----utilizing compute heat/flux command to calculate average thermal conductivity. I make some modification to simulate iron’s thermal conductivity. But the result puzzled me. Besides some necessary modification, I only amend the N of “run N” command, nevertheless the results were vastly different.
So I write to ask for some help. Is it correct what I have modified or the example input script couldn’t be use like this? Or why in the same temperature, the results is so different?
The result of the first attachment is 124.5W/Km, the second is 2715W/Km, the third is 4545W/Km
the input script:
atom_style atomic
units metal
variable kB equal 1.3806504e-23 # [J/K] Boltzmann
variable kCal2J equal 4186.0/6.02214e23
variable T equal 300
variable V equal vol
variable dt equal 0.0001
variable p equal 200 # correlation length
variable s equal 10 # sample interval
variable d equal $p$s # dump interval
---------------------------------------------------------
dimension 3
boundary p p p
lattice fcc 2.87 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
region box block 0 4 0 4 0 4
create_box 1 box
create_atoms 1 box
mass 1 55.85
pair_style eam
pair_coeff * * Fe_2.eam
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 N
-------------- flux 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
fix JJ all ave/correlate $s $p d c_flux[1] c_flux[2] c_flux[3] type auto file J0Jt.dat ave running
variable scale equal {kCal2J}{kCal2J}/{kB}/$T/$T/$Vs*{dt}1.0e25
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 N’
variable k equal (v_k11+v_k22+v_k33)/3.0
print “average conductivity: $k [W/mK]”
in.tc（1） (1.68 KB)
in.tc（2） (1.68 KB)
in.tc（3） (1.68 KB)
Dear all:
In the manual, there is an example LAMMPS input script for solid Ar-----utilizing compute heat/flux command to calculate average thermal conductivity. I make some modification to simulate iron’s thermal conductivity. But the result puzzled me. Besides some necessary modification, I only amend the N of “run N” command, nevertheless the results were vastly different.
So I write to ask for some help. Is it correct what I have modified or the example input script couldn’t be use like this? Or why in the same temperature, the results is so different?
The result of the first attachment is 124.5W/Km, the second is 2715W/Km, the third is 4545W/Km.
Maosheng
the input script:
atom_style atomic
units metal
variable kB equal 1.3806504e-23 # [J/K] Boltzmann
variable kCal2J equal 4186.0/6.02214e23
variable T equal 300
variable V equal vol
variable dt equal 0.0001
variable p equal 200 # correlation length
variable s equal 10 # sample interval
variable d equal $p$s # dump interval
---------------------------------------------------------
dimension 3
boundary p p p
lattice fcc 2.87 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
region box block 0 4 0 4 0 4
create_box 1 box
create_atoms 1 box
mass 1 55.85
pair_style eam
pair_coeff * * Fe_2.eam
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 N
-------------- flux 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
fix JJ all ave/correlate $s $p d c_flux[1] c_flux[2] c_flux[3] type auto file J0Jt.dat ave running
variable scale equal {kCal2J}{kCal2J}/{kB}/$T/$T/$Vs*{dt}1.0e25
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 N’
variable k equal (v_k11+v_k22+v_k33)/3.0
print “average conductivity: $k [W/mK]”
in.tc（1） (1.68 KB)
in.tc（2） (1.68 KB)
in.tc（3） (1.68 KB)
Mail list readers (like me) generally don't have
time to read thru complicated scripts to figure
out what you are doing or what might be going wrong.
You need to post a more specific question. Someone
familiar with thermal conductiity may want to comment
on whether you can use this technique for Fe, since
the thermal conductivity of metals presumably depends
on electronic contributions.
Steve
Dear all:
In the manual, there is an example LAMMPS input script for solid
Ar-----utilizing compute heat/flux command to calculate average thermal
conductivity. I make some modification to simulate iron's thermal
conductivity. But the result puzzled me. Besides some necessary
modification, I only amend the N of "run N" command, nevertheless the
results were vastly different.
So I write to ask for some help. Is it correct what I have modified or
the example input script couldn't be use like this? Or why in the same
temperature, the results is so different?
if you run for different length and get different results, then
this is often an indication that your results are not converged
within the time you simulate and/or the size of the system you
are looking at. increasing the values of N in a systematic
way, should have them converge at some point. you can also
break down longer trajectories into chunks and analyse them
independently to get a feeling for how large fluctuations you
get on your results.
cheers,
axel.