# (no subject)

My project is thermal conductivity in nano- ribbon graphene .I have a problem, I do not know for a nano- ribbon graphene with a length of 12nm and width of 8nm,What number should be p ? what is the numerical relationship between the length of graphene and p?
#SAMPLE lammps input script for thermal conductivity of GNR via the GK formalism

units metal
variable T equal 300
variable V equal vol
variable p equal 100 # correlation length
variable s equal 2 # sample interval
variable d equal \$p*\$s # dump interval
variable dt equal 0.001

# convert from LAMMPS real units to SI

variable kB equal 1.3806504e-23 # [J/K] Boltzmann
variable ev2J equal 1.60217653e-19
variable A2m equal 1.0e-10
variable ps2s equal 1.0e-12
variable convert equal {ev2J}*{ev2J}/{ps2s}/{A2m}

# setup problem

dimension 3
atom_style atomic
boundary p p p
region box block -100 100 -50 250 -30 30 units box

mass 1 12.000
pair_style tersoff
pair_coeff * * sic.tersoff C

timestep 0.001
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 50000
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”

My project is thermal conductivity in nano- ribbon graphene .I have a problem, I do not know for a nano- ribbon graphene with a length of 12nm and width of 8nm,What number should be p ? what is the numerical relationship between the length of graphene and p?

There is no simple use-this-not-that answer to this question.
Please see the many previous recent discussions on the subject in the mailing list archives.