Why this DPD run doesn't start

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1 
units lj

timestep 0.001

dimension 2
boundary p p p
atom_style atomic
neighbor 0.3 bin
neigh_modify every 20 delay 0 check no

lattice hex 0.5
region simbox block 0 50 0 25 -0.1 0.1
create_box 2 simbox

lattice hex 0.5
create_atoms 1 region simbox

lattice hex 0.5 origin 0.5 0.5 0
create_atoms 2 region simbox

mass 1 1
mass 2 1

comm_modify vel yes
velocity all create 0.7 123456 dist gaussian
pair_style hybrid dpd 1 2.5 123456 soft 0.5

pair_coeff 1 1 dpd 0.7 2.5 12345
pair_coeff 2 2 dpd 0.7 2.5 12346
pair_coeff 1 2 soft 0.5

fix 1 all nvt temp 0.7 0.7 0.1

dump 1 all atom 5000 dump.lammpstrj
write_data dpd_data.all
thermo 500
run 5000000

I get this and nothing happens. Does I set the DPD properly? If I use LJ instead it works

Lattice spacing in x,y,z = 1.51967 2.63215 1.51967
Created orthogonal box = (0 0 -0.151967) to (75.9836 65.8037 0.151967)
  1 by 1 by 1 MPI processor grid
Lattice spacing in x,y,z = 1.51967 2.63215 1.51967
Created 2500 atoms
  Time spent = 0.00096488 secs
Lattice spacing in x,y,z = 1.51967 2.63215 1.51967
Created 2500 atoms
  Time spent = 0.000313997 secs
System init for write_data ...
Neighbor list info ...
  update every 20 steps, delay 0 steps, check no
  max neighbors/atom: 2000, page size: 100000
  master list distance cutoff = 8.28239e+06
  ghost atom cutoff = 8.28239e+06
  binsize = 4.14119e+06, bins = 1 1 1
  3 neighbor lists, perpetual/occasional/extra = 3 0 0
  (1) pair dpd, perpetual, skip from (3)
      attributes: half, newton on
      pair build: skip
      stencil: none
      bin: none
  (2) pair soft, perpetual, skip from (3)
      attributes: half, newton on
      pair build: skip
      stencil: none
      bin: none
  (3) neighbor class addition, perpetual
      attributes: half, newton on
      pair build: half/bin/atomonly/newton
      stencil: half/bin/2d/newton
      bin: standard
2

units lj

timestep 0.001

dimension 2
boundary p p p
atom_style atomic
neighbor 0.3 bin
neigh_modify every 20 delay 0 check no

lattice hex 0.5
region simbox block 0 50 0 25 -0.1 0.1
create_box 2 simbox

lattice hex 0.5
create_atoms 1 region simbox

lattice hex 0.5 origin 0.5 0.5 0
create_atoms 2 region simbox

mass 1 1
mass 2 1

comm_modify vel yes
velocity all create 0.7 123456 dist gaussian
pair_style hybrid dpd 1 2.5 123456 soft 0.5

pair_coeff 1 1 dpd 0.7 2.5 12345
pair_coeff 2 2 dpd 0.7 2.5 12346

these two pair_coeff statements override the default pairwise
interaction cutoff from 2.5 sigma to 1.2345e5 sigma. this is
*HUUUUUGE* and not likely what you were planning.

pair_coeff 1 2 soft 0.5

fix 1 all nvt temp 0.7 0.7 0.1

dump 1 all atom 5000 dump.lammpstrj
write_data dpd_data.all
thermo 500
run 5000000

I get this and nothing happens. Does I set the DPD properly? If I use LJ instead it works

no, your input is broken. you can see this when you look at the log,
you see those gigantic numbers for neighbor list cutoffs and ghost
atom communication cutoff.
LAMMPS isn't stuck, but it is assembling insanely large neighbor
lists, possibly driving your machine into excessive swapping and thus
slowing it down even more.

axel.

3

Indeed. To answer your previous question: pair_style != pair_coeff. They have different arguments.