Atoms won't move even though fixes are defined

Good Day LAMMPS Users

I am performing an isothermal aging simulation on steel but before I dive into adding all the elements that makeup steel I am running a test on the FeCr.cdeam potential file to see if my code runs smoothly. The output gives an error ’ WARNING: No fixes defined, atoms won’t move (…/verlet.cpp:52)’ even though the fixes are clearly defined. Does anyone know why this happens? My code is as follows

units real
dimension 3
processors * * *
boundary p p p
atom_style atomic

region whole block 0 50 0 50 -0.80 0.80
create_box 2 whole

#create Fe atoms
lattice bcc 2.935
create_atoms 1 region whole

#create Cr atoms
lattice bcc 3.224 origin 0.55 0.55 0.55
create_atoms 2 region whole

pair_style eam/cd
pair_coeff * * …/potentials/FeCr.cdeam Fe Cr

Equilibrium

reset_timestep 0
timestep 0.009

minimize 0.0 1e-3 1000 10000

velocity all create 300 23456 mom no rot no

fix 1 all npt temp 300 300 100 iso 1.01 1.01 1000
run 20000
unfix 1

fix 1 all npt temp 300 775 100 iso 1.01 1.01 1000
run 350000
unfix 1

thermo 2000
thermo_style custom step temp

print “Equilibrium reached”

#isothermal ageing
reset_timestep 0
fix 1 all npt temp 775 775 1000 iso 1.01 1.01 1000
run 10000
unfix 1

thermo 2000
thermo_style custom step temp

dump 1 all custom 250 dump.Fetest.* id xs ys zs

thermo 500
thermo_style custom step temp

run 4000

Good Day LAMMPS Users

I am performing an isothermal aging simulation on steel but before I dive into adding all the elements that makeup steel I am running a test on the FeCr.cdeam potential file to see if my code runs smoothly. The output gives an error ’ WARNING: No fixes defined, atoms won’t move (…/verlet.cpp:52)’ even though the fixes are clearly defined. Does anyone know why this happens? My code is as follows

what LAMMPS versions is this with? I don’t see that WARNING message with the latest patch release.
However, I see the more worrisome warning: WARNING: Proc sub-domain size < neighbor skin, could lead to lost atoms (src/domain.cpp:963)
because your system is too shallow in z-direction. since it is a periodic box, you should make that wider, since you are suppressing fluctuations in that direction that are crucial to proper sampling.

axel.

Hello,

In addition to Axel’s reply - I believe the source of your particular error message is your last run command.

In this section, you have turned off your npt command with “unfix 1” before you call your “run 4000” command, so you have no integration fix defined anymore.

I am using the LAMMPS stable version(03 March 2020). I made the z width wider as you suggested and the warning: WARNING: Proc sub-domain size < neighbor skin, could lead to lost atoms (src/domain.cpp:963) , went away. Thank you so much Dr. Axel.

I see I have mistakenly placed an unfix command with the last npt fix without a run command. The warning: WARNING: No fixes defined, atoms won’t move (…/verlet.cpp:52), no longer appears. Many thanks, Ezekiel.