Does anyone know why pressure does not equilibrate in NVT calculations using LAMMPS? I have tried anything from adjusting the Tdamp value to dt to different forcefield parameters and different sizes of the box. I also see negative potential evolved with time. I am simulating nvt of TIP4p water model.
Thanks, but I still see oscillations. Do I need to monitor "press" variable or need to care only about the time-averaged pressure?
Thanks Zhe. I solved oscillating pressure, but now I face the following error when trying to do NPT after NVT:
ERROR: Non-numeric pressure - simulation unstable (../fix_nh.cpp:1043)
I believe the pressure goes to infinity .
Did you optimized the structure before your NPT simulations? Also, it is good idea to pre-equilibrate the system by a short NVT simulation before NPT.
Viorel Chihaia Yes, that is what I am trying to do.I do minimization and then a short NVT before NPT.
Hi Meisa,.
I‘ve met the same problem about the oscillating pressure in NPT simulations. Could you explain the usage of time-averaged pressure in detail? Meisam Adibifard Thank you.
Yuyang Wang You need to chase down average pressure instead of instantaneous pressure. Average pressure can be calculated using "fix ave/time " command. If average pressure is still oscillating, you can add "drag 2.0" to your "fix npt" command. See LAMMPS manual for further information on this.
How can I solve this problem? ERROR: Non-numeric pressure - simulation unstable (src/fix_nh.cpp:1062)
# ------------------------ INITIALIZATION ----------------------------
units metal
dimension 3
boundary p p p
atom_style atomic
variable latparam equal 4.05
# ----------------------- ATOM DEFINITION ----------------------------
read_data Al75Pd25.dat
Reading data file ...
orthogonal box = (0.0000000 0.0000000 0.0000000) to (23.681459 23.681459 23.681459)
1 by 1 by 1 MPI processor grid
reading atoms ...
1099 atoms
read_data CPU = 0.004 seconds
# ------------------------ FORCE FIELDS ------------------------------
pair_style meam/c
pair_coeff * * library.meam Al Pd PdAl.meam Al Pd
# ------------------------- SETTINGS ---------------------------------
compute 1 all stress/atom NULL
compute 2 all reduce sum c_1[1] c_1[2] c_1[3]
######################################
# EQUILIBRATION
reset_timestep 0
timestep 0.001
velocity all create 300 12345 mom yes rot no
fix 1 all npt temp 300 300 1 iso 0 0 1 drag 1
# Set thermo output
thermo 1000
thermo_style custom step lx ly lz press pxx pyy pzz pe temp
# Run for at least 10 picoseconds (assuming 1 fs timestep)
run 20000
Neighbor list info ...
update every 1 steps, delay 10 steps, check yes
max neighbors/atom: 2000, page size: 100000
master list distance cutoff = 6.5
ghost atom cutoff = 6.5
binsize = 3.25, bins = 8 8 8
2 neighbor lists, perpetual/occasional/extra = 2 0 0
(1) pair meam/c, perpetual
attributes: full, newton on
pair build: full/bin/atomonly
stencil: full/bin/3d
bin: standard
(2) pair meam/c, perpetual, half/full from (1)
attributes: half, newton on
pair build: halffull/newton
stencil: none
bin: none
ERROR: Non-numeric pressure - simulation unstable (src/fix_nh.cpp:1062)
Last command: run 20000
ERROR: Non-numeric pressure - simulation unstable (src/fix_nh.cpp:1062) How did you guys fix this error?
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