Dear lammps developers and users
First of all thanks to Axel Kohimeyer for his suggestion.
I have simulated water at constant temperature and pressure using nve with Berendsen thermostat and berendsen barostat . The system is equilibrating , but the volume of the simulation box changes to 6-7 times the initial volume of the box.Input file is attaching with this. If any correction is required ,please help me.
#Input file for SPC/E water
boundary p p p
restart 50000 restart
#Simulation Units andSimulation Type
units metal
atom_style full
#Reads configuration from file
read_data water500.txt
#read_restart restart.*
#Mass relative mass of atoms
mass 2 15.99943
mass 1 1.00794
group oxygen type 2
group hydrogen type 1
set group oxygen charge -0.8476
set group hydrogen charge 0.4238
#Define potential type
pair_style lj/charmm/coul/long 10.0 12.0 12.0
kspace_style pppm 5.0e-5
kspace_modify mesh 36 36 36 order 5
#Lennard-Jones Parameters
pair_coeff 2 2 0.0067371579 3.166
pair_coeff 1 1 0.0000000000 0.000
pair_coeff 1 2 0.0000000000 0.000
bond_style harmonic
bond_coeff 1 100.0 1.0
angle_style harmonic
angle_coeff 1 300.0 109.47
group water type 1 2
velocity all create 800 234324 dist gaussian mom yes rot yes
neighbor 2.0 bin
neigh_modify delay 0 page 200000 one 4000
#minimize 0 0 1000 10000
thermo_style custom step pe ke etotal temp press
#Applies or “fixes” NVT MD
fix 1 water shake 0.0001 20 500 b 1 a 1
fix a all nve
#Dumps output files and thermodynamic properties
dump 1 all atom 500 dump.waterNPT4
thermo 500
#Timestep is 1 fs (0.001 ps)
timestep 0.001
#Number of time steps (reduced)
#run 20000
compute mobile all temp
fix b all temp/berendsen 373 373 100
fix_modify b temp mobile
#run 20000
compute baro all pressure mobile
fix jsb water press/berendsen iso 1 1 1000
fix jsb water press/berendsen xyz 1 1 2000
fix_modify jsb press baro
thermo_style custom step pe ke etotal temp press vol xlo xhi ylo yhi zlo zhi
run 2000000
Advance thanks to all
Jesseela