Deal All:
There’re some points that I do not understand regarding the command of compute heat/flux.
Let me describe it with the example given by the manual:
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The atom_style should not be dqd, right? coz the new version of lammps does not include this type.
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Why should the heat flux divided by volume “V” ?
variable J equal c_flux[1]/vol
thermo_style custom step temp v_J
Besides, there’s also a “V” in the numerator, so is the volume term cancelled after multiplying the heat flux with V/(kB T^2) ? According to some other articles, the formula of the thermal conductivity k should include the volume “V” at the denominator, but why it’s expressed different in Lammps?
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I’ve tried to output the volume during the simulation. It’s 10290.076 in this case which is a little different from the domain defined by “region box block 0 4 0 4 0 4”. So what’s exact the meaning of the volume?
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Is anybody can help me derive the exact coeff. of 2917703220.0 for me? In the manual, it said “The integral of the correlation needs to be multiplied by V/(kB T^2) times the sample interval and the appropriate unit” conversion factor". I appreciate it very much if someone can help me figure out how to derive this coeff.
Sample LAMMPS input script
atom_style dpd
units real
dimension 3
boundary p p p
lattice fcc 5.376 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 39.948
pair_style lj/cut 13.0
pair_coeff * * 0.2381 3.405
group every region box
velocity all create 70 102486 mom yes rot yes dist gaussian
timestep 4.0
thermo 10
# ------------- Equilibration and thermalisation ----------------
fix NPT all npt 70 70 10 xyz 0.0 0.0 100.0 drag 0.2
run 8000
unfix NPT
# --------------- Equilibration in nve -----------------
fix NVE all nve
run 8000
# -------------- Flux calculation in nve ---------------
reset_timestep 0
compute myPE all pe/atom pair
compute flux all heat/flux myPE
log flux.log
variable J equal c_flux[1]/vol
thermo_style custom step temp v_J
run 100000