# 8.5.2. 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 3 atoms. In LAMMPS the fix shake 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.

These are the additional parameters (in real units) to set for O and H atoms and the water molecule to run a rigid TIP3P-CHARMM model with a cutoff. The K values can be used if a flexible TIP3P model (without fix shake) is desired. If the LJ epsilon and sigma for HH and OH are set to 0.0, it corresponds to the original 1983 TIP3P model (Jorgensen).

O mass = 15.9994
H mass = 1.008
O charge = -0.834
H charge = 0.417
LJ $$\epsilon$$ of OO = 0.1521
LJ $$\sigma$$ of OO = 3.1507
LJ $$\epsilon$$ of HH = 0.0460
LJ $$\sigma$$ of HH = 0.4000
LJ $$\epsilon$$ of OH = 0.0836
LJ $$\sigma$$ of OH = 1.7753
K of OH bond = 450
$$r_0$$ of OH bond = 0.9572
K of HOH angle = 55
$$\theta$$ of HOH angle = 104.52$$^{\circ}$$

These are the parameters to use for TIP3P with a long-range Coulomb solver (e.g. Ewald or PPPM in LAMMPS), see (Price) for details:

O mass = 15.9994
H mass = 1.008
O charge = -0.830
H charge = 0.415
LJ $$\epsilon$$ of OO = 0.102
LJ $$\sigma$$ of OO = 3.188
LJ $$\epsilon$$, $$\sigma$$ of OH, HH = 0.0
K of OH bond = 450
$$r_0$$ of OH bond = 0.9572
K of HOH angle = 55
$$\theta$$ of HOH angle = 104.52$$^{\circ}$$

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).