\(\renewcommand{\AA}{\text{Å}}\)

8.4.3. TIP3P water model

The TIP3P water model as implemented in CHARMM (MacKerell) specifies a 3-site rigid water molecule with charges and Lennard-Jones parameters assigned to each of the three atoms.

A suitable pair style with cutoff Coulomb would be:

pair_style lj/cut/coul/cut

or these commands for a long-range Coulomb model:

In LAMMPS the fix shake or fix rattle command can be used to hold the two O-H bonds and the H-O-H angle rigid. A bond style of harmonic and an angle style of harmonic or charmm should also be used. In case of rigid bonds also bond style zero and angle style zero can be used.

The table below lists the force field parameters (in real units) to for the water molecule atoms to run a rigid or flexible TIP3P-CHARMM model with a cutoff, the original 1983 TIP3P model (Jorgensen), or a TIP3P model with parameters optimized for a long-range Coulomb solver (e.g. Ewald or PPPM in LAMMPS) (Price). The K values can be used if a flexible TIP3P model (without fix shake) is desired, for rigid bonds/angles they are ignored.

Parameter	TIP3P-CHARMM	TIP3P (original)	TIP3P (Ewald)
O mass (amu)	15.9994	15.9994	15.9994
H mass (amu)	1.008	1.008	1.008
O charge (\(e\))	-0.834	-0.834	-0.834
H charge (\(e\))	0.417	0.417	0.417
LJ \(\epsilon\) of OO (kcal/mole)	0.1521	0.1521	0.1020
LJ \(\sigma\) of OO (\(\AA\))	3.1507	3.1507	3.188
LJ \(\epsilon\) of HH (kcal/mole)	0.0460	0.0	0.0
LJ \(\sigma\) of HH (\(\AA\))	0.4	1.0	1.0
LJ \(\epsilon\) of OH (kcal/mole)	0.0836	0.0	0.0
LJ \(\sigma\) of OH (\(\AA\))	1.7753	1.0	1.0
K of OH bond (kcal/mole/\(\AA^2\))	450	450	450
\(r_0\) of OH bond (\(\AA\))	0.9572	0.9572	0.9572
K of HOH angle (kcal/mole)	55.0	55.0	55.0
\(\theta_0\) of HOH angle	104.52\(^{\circ}\)	104.52\(^{\circ}\)	104.52\(^{\circ}\)

Below is the code for a LAMMPS input file and a molecule file (tip3p.mol) of TIP3P water for use with the molecule command demonstrating how to set up a small bulk water system for TIP3P with rigid bonds.

units real
atom_style full
region box block -5 5 -5 5 -5 5
create_box 2 box bond/types 1 angle/types 1 &
            extra/bond/per/atom 2 extra/angle/per/atom 1 extra/special/per/atom 2

mass 1 15.9994
mass 2 1.008

pair_style lj/cut/coul/cut 8.0
pair_coeff 1 1 0.1521 3.1507
pair_coeff 2 2 0.0    1.0

bond_style zero
bond_coeff 1 0.9574

angle_style zero
angle_coeff 1 104.52

molecule water tip3p.mol
create_atoms 0 random 33 34564 NULL mol water 25367 overlap 1.33

fix rigid all shake 0.001 10 10000 b 1 a 1
minimize 0.0 0.0 1000 10000

reset_timestep 0
timestep 1.0
velocity all create 300.0 5463576
fix integrate all nvt temp 300 300 100.0

thermo_style custom step temp press etotal pe

thermo 1000
run 20000
write_data tip3p.data nocoeff

# Water molecule. TIP3P geometry

atoms
bonds
angles

Coords

  0.00000  -0.06556   0.00000
  0.75695   0.52032   0.00000
 -0.75695   0.52032   0.00000

Types

      1   # O
      2   # H
      2   # H

Charges

     -0.834
      0.417
      0.417

Bonds

 1      1      2
 1      1      3

Angles

 1      2      1      3

Shake Flags

1
1
1

Shake Atoms

1 2 3
1 2 3
1 2 3

Shake Bond Types

1 1 1
1 1 1
1 1 1

Special Bond Counts

2 0 0
1 1 0
1 1 0

Special Bonds

2 3
1 3
1 2

Wikipedia also has a nice article on water models.

(MacKerell) MacKerell, Bashford, Bellott, Dunbrack, Evanseck, Field, Fischer, Gao, Guo, Ha, et al, J Phys Chem, 102, 3586 (1998).

(Jorgensen) Jorgensen, Chandrasekhar, Madura, Impey, Klein, J Chem Phys, 79, 926 (1983).

(Price) Price and Brooks, J Chem Phys, 121, 10096 (2004).