Hi everyone,
I want to do NVT and NPT simulations of liquid water using the TIP4P/ice water model. But the simulations crash unless I use a very small (<0.05fs) timestep. I use all the tricks in the book i.e. energy minimization before the actual simulation etc, but irrespective, the simulations crash after a while unless I choose a very small [unpractical] timestep stating that one hydrogen is missing. Below I include my input script and data file for one such simulation.
PS, I am using the most recent release of LAMMPS released on July 4, 2012. Also the problem persists even if I don’t use ‘replicate’ and use energy minimization on a configuration that I have obtained otherwise.
Regards
Amir
DATA FILE single1.dat
One tip4p/ice water molecule
0 3.9199999 xlo xhi
0 3.9199999 ylo yhi
0 3.9199999 zlo zhi
2 atom types
3 atoms
1 bond types
2 bonds
1 angle types
1 angles
Masses
1 15.9994
2 1.0079
Atoms
1 1 1 -1.1794 2.0000 2.0000 2.0000
2 1 2 0.5897 1.243049672736339 1.414117723381705 2.0000
3 1 2 0.5897 2.756950327263661 1.414117723381705 2.0000
Velocities
1 0 0 0
2 0 0 0
3 0 0 0
Bond Coeffs
1 100 0.9572
Bonds
1 1 1 2
2 1 1 3
Angle Coeffs
1 300 104.52
Angles
1 1 2 1 3
==== INPUT SCRIPT ====
Simulation of tip4p/ice water NPT seed 1
units real
dimension 3
boundary p p p
atom_style full
atom_modify map array
bond_style harmonic
angle_style harmonic
pair_style lj/cut/coul/long/tip4p 1 2 1 1 0.1577 8.5 8.5
read_data single1.dat
replicate 16 16 16
group oxy type 1 # Name atom types
group hyd type 2
group water union oxy hyd
pair_coeff 1 1 0.210701615058703 3.1668
pair_coeff 2 2 0.0 0.0
kspace_style pppm/tip4p 1e-4 # Electrostatics
dielectric 1.0
pair_modify tail yes # long-range correction for truncated Lennard-Jones interactions
fix 5 all shake 1e-12 200000 0 b 1 a 1 # Make molecules rigid using shake
thermo_style custom step temp press vol ke pe emol etotal
neighbor 1.0 bin
neigh_modify delay 0 every 1 check yes
thermo 100
timestep 1.0 #nothing greater than 0.05 works
dump 1 all xyz 100 position.xyz
fix 6 all npt temp 220.0 220.0 200.0 iso 1.0 1.0 1000.0
restart 100 tip4piceNPT1a.out tip4piceNPT1b.out
run 1000000