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:

The atom_style should not be dqd, right? coz the new version of lammps does not include this type.

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?

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?

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