Dear all,
I have a polymer system, whose mechanical properties were obtained using uniaxial tension procedure (All atom model, 60,000 atoms). Am using CHARMM forcefield. The mechanical properties matches with the experimental observations. So, I guess the parameters are correct.
Now I am incorporating 6000 water molecules in the polymer system (Approx. 30% mass of the polymer system). Am using TIP3p water model with long range interactions mentioned in the lammps site. The settings are as follows.
units real
atom_style full
bond_style harmonic
angle_style charmm
dihedral_style charmm
pair_style lj/cut/coul/long 10.5
kspace_style pppm 1.0e-4
neigh_modify every 1 delay 0 check yes
dump 2 all dcd 100 dump_for_min.dcd
dump_modify 2 unwrap yes
thermo 10
thermo_style custom step pe lx ly lz press pxx pyy pzz
min_style cg
minimize 1e-25 0.0 1000000 100000000000
undump 2
dump 2 all dcd 1000 dump_for_equi.dcd
dump_modify 2 unwrap yes
velocity all create 1.0 1231
fix 1 all nve/limit 0.05
fix 2 all langevin 1.0 1.0 10.0 904297
thermo_style custom step temp press vol density
thermo 100
timestep 0.5
run 10000
unfix 1
unfix 2
fix 1 all npt temp 1 100 100 iso 0 0 1000 drag 2
thermo_style custom step temp press etotal vol density
thermo 10
timestep 0.5
run 50000
unfix 1
fix 1 all npt temp 100 100 100 iso 0 0 1000 drag 2
thermo_style custom step temp press etotal vol density
thermo 10
timestep 0.5
run 50000
unfix 1
fix 1 all npt temp 100 150 100 iso 0 0 1000 drag 2
thermo_style custom step temp press etotal vol density
thermo 10
timestep 0.5
run 50000
unfix 1
fix 1 all npt temp 150 150 100 iso 0 0 1000 drag 2
thermo_style custom step temp press etotal vol density
thermo 10
timestep 0.5
run 50000
unfix 1
fix 1 all npt temp 150 200 100 iso 0 0 1000 drag 2
thermo_style custom step temp press etotal vol density
thermo 10
timestep 0.5
run 50000
unfix 1
fix 1 all npt temp 200 200 100 iso 0 0 1000 drag 2
thermo_style custom step temp press etotal vol density
thermo 10
timestep 0.5
run 50000
unfix 1
fix 1 all npt temp 200 250 100 iso 0 0 1000 drag 2
thermo_style custom step temp press etotal vol density
thermo 10
timestep 0.5
run 50000
unfix 1
fix 1 all npt temp 250 250 100 iso 0 0 1000 drag 2
thermo_style custom step temp press etotal vol density
thermo 10
timestep 0.5
run 50000
unfix 1
fix 1 all npt temp 250 300 100 iso 0 0 10 drag 2
thermo_style custom step temp press etotal vol density
thermo 10
timestep 0.5
run 50000
unfix 1
fix 1 all npt temp 300 300 1000 iso 0 0 100
thermo_style custom step temp press etotal vol density
thermo 10
timestep 0.5
run 300000
unfix 1
undump 2
write_data afterequi.txt
dump 2 all dcd 100 dump_for_deform.dcd
dump_modify 2 unwrap yes
variable tmp equal “lx”
variable L0 equal ${tmp}
variable strain equal “(lx - v_L0)/v_L0”
variable p1 equal “v_strain”
variable p2 equal “-pxx/100001.01325"
variable p3 equal "-pyy/100001.01325”
variable p4 equal “-pzz/10000*1.01325”
variable p5 equal “lx”
variable p6 equal “ly”
variable p7 equal “lz”
variable p8 equal “temp”
variable t2 equal “epair”
variable t3 equal “ebond”
variable t4 equal “eangle”
variable t5 equal “edihed”
fix 1 all npt temp 300 300 100 y 1 1 1000 z 1 1 1000 drag 2
fix 2 all deform 1 x erate 1e-4 units box remap x
fix def1 all print 1 “{p1} {p2} {p3} {p4} {p5} {p6} {p7} {p8}” file system.def1.txt screen no
fix def2 all print 1 “{p1} {t2} {t3} {t4} ${t5}” file system.def2.txt screen no
thermo_style custom step temp pxx pyy pzz lx ly lz epair ebond eangle edihed
thermo 100
timestep 0.5
run 20000
It is expected that in the presence of water molecules the mechanical properties are supposed to decrease. But, in this polymer and water system, the mechanical properties like maximum stress is higher than the pristine polymer system.
Though, mail is not relevant to Lammps, If someone could suggest some possible reasons or mistakes I would have made, could be really helpful to me.
Thank you,