Hello,
I’m focusing on a system containing 1 polymer chain and around 200 solvent molecules.
I wish to relax the system to 300 K and 1 atm using NPT with OPLS force field.
In order to accelerate the simulation I use pppm instead of ewald. The initial timestep = 1 fs
The cubic simulation box begins to shrink and its volume keeps decreasing until the “cannot compute pppm” error occured.
I then continue the relaxation with timestep = 0.1 fs, however the volume begins to increase after restarting and seems to stabilize… This is extremely strange because I only modify the timestep and the system refuses to continue the shrinkage after restarting… I tried using both the binary restart file and text lammps data file for restarting the simulation. I also tried to continue with ewald instead of pppm… But in all cases the system doesn’t retrieve the trend of volume shrinkage.
Could anyone give me some advices on the relaxation ?
Please find below my input script:
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include “system.in.init”
read_data “system.data”
include “system.in.settings”
variable max_it equal 100000
min_style cg # conjugate gradient (CG) algorithm
minimize 1e-25 1e-25 {max_it} {max_it} # only to first initialize simulation, turned off when continuing from restart file
dump 1 all dcd 1000 system.dcd
thermo_style custom vol density temp press # specify thermodynamic variables that you want to output
thermo 1000
timestep 1
velocity all create 300.0 4928459 rot yes dist gaussian # only to first initialize simulation, turned of when continuing from restart file
fix 1 all npt temp 300.0 300.0 100.0 iso 1.0 1.0 100.0
restart 100000 crosslinker_solvent.restart
run 500000
write_data relax_restart.data
#---------------------------------------------------
units real
atom_style full
kspace_style pppm 1.0e-4
neigh_modify every 1 delay 0 check yes
pair_style lj/cut/coul/long 10.0
bond_style harmonic
angle_style harmonic
dihedral_style opls