Hi,
For simulating a polymer-graphene system in aqueous solution, I’m using NVE+Langevin thermostat for equilibrium (state 1) and then NPT for equilibrium and production runs (state 2).
However, at the time the ensemble is altered from state 1 to 2, the whole system starts to move badly, esp. in y and z directions (and coming from other sides due to pbc). I have attached a short video from the simulation (about 5 ns), and this bad behavior happens after about 1 s of the video (solvent is not shown).
I appreciate if you take a look at this. I didn’t notice this behavior when I used NPT only or Berendsen instead of Langevin.
The input file is as follows:
#LAMMPS 9 Dec 2014
PVC
boundary p p p
units real
atom_style full
bond_style class2
angle_style class2
dihedral_style class2
improper_style class2
pair_style soft 12
pair_style lj/class2/coul/long 12
pair_modify tail yes table 12
newton on
read_data PVC.data
group all type 1 2 3 4 5 6 7 8 9 10 11
group Pchain type 2 3 4 5 6 7 8 9
group P_G type 1 2 3 4 5 6 7 8 9
group G type 1
group water type 10 11
kspace_style ewald 1e-4
special_bonds dreiding
neighbor 1 bin
neigh_modify delay 0 every 1 check yes page 1000000
comm_modify mode single cutoff 12 vel no
thermo 100
thermo_style custom step temp press vol density etotal ke pe enthalpy evdwl ecoul epair ebond eangle edihed eimp emol elong etail time
restart 2000 restart-min.*
minimize 1.0e-06 1.0e-06 100000 100000
velocity all create 290 123469 units box
reset_timestep 0
fix sh all shake 0.000001 1000 0 t 10 11 b 14 a 29
####state 1###
fix Eq1 all nve
fix Eq11 all langevin 290 290 100 481579
dump Eq1112 all custom 10000 dump-total.lammpstrj id mol type element mass q x y z xs ys zs
compute comP01 Pchain com
fix comP01 Pchain ave/time 5 99 500 c_comP01[1] c_comP01[2] c_comP01[3] file tmp.comP01
thermo 500
thermo_style custom step temp press vol density etotal ke pe enthalpy evdwl ecoul epair ebond eangle edihed eimp emol elong etail time
thermo_modify lost warn flush yes
timestep 0.00005
restart 100000 restart-eq1.*
run 100000
thermo 500
timestep 0.0001
restart 100000 restart-eq1.*
run 100000
thermo 500
timestep 0.0005
restart 100000 restart-eq1.*
run 100000
thermo 500
timestep 0.001
restart 100000 restart-eq1.*
run 100000
thermo 500
timestep 0.005
restart 100000 restart-eq1.*
run 100000
thermo 500
timestep 0.01
restart 100000 restart-eq1.*
run 100000
thermo 500
timestep 0.05
restart 100000 restart-eq1.*
run 100000
thermo 500
timestep 0.1
restart 100000 restart-eq1.*
run 100000
thermo 500
timestep 0.5
restart 100000 restart-eq1.*
run 200000
thermo 500
timestep 1
restart 100000 restart-eq1.*
run 2000000
unfix Eq1
unfix Eq11
####state 2###
fix Eq2 all npt temp 290 290 500 iso 1 1 5000
thermo 500
timestep 1
restart 100000 restart-eq1.*
run 5000000
unfix sh
unfix Eq2
write_data data.end
write_restart restart.end
Langevin.wmv (2.12 MB)