# TIP3P water model The TIP3P water model as implemented in CHARMM [(MacKerell)](howto-tip3p) specifies a 3-site rigid water molecule with charges and Lennard-Jones parameters assigned to each of the 3 atoms. A suitable pair style with cutoff Coulomb would be: - [pair_style lj/cut/coul/cut](pair_lj_cut_coul) or these commands for a long-range Coulomb model: - [pair_style lj/cut/coul/long](pair_lj_cut_coul) - [pair_style lj/cut/coul/long/soft](pair_fep_soft) - [kspace_style pppm](kspace_style) - [kspace_style pppm/disp](kspace_style) In LAMMPS the [fix shake or fix rattle](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](bond_harmonic) and an angle style of [harmonic](angle_harmonic) or [charmm](angle_charmm) should also be used. In case of rigid bonds also bond style [zero](bond_zero) and angle style [zero](angle_zero) can be used. The table below lists the force field parameters (in real [units](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)](Jorgensen1), or a TIP3P model with parameters optimized for a long-range Coulomb solver (e.g. Ewald or PPPM in LAMMPS) [(Price)](Price1). 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](molecule) demonstrating how to set up a small bulk water system for TIP3P with rigid bonds. ``` LAMMPS 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 3 atoms 2 bonds 1 angles Coords 1 0.00000 -0.06556 0.00000 2 0.75695 0.52032 0.00000 3 -0.75695 0.52032 0.00000 Types 1 1 # O 2 2 # H 3 2 # H Charges 1 -0.834 2 0.417 3 0.417 Bonds 1 1 1 2 2 1 1 3 Angles 1 1 2 1 3 Shake Flags 1 1 2 1 3 1 Shake Atoms 1 1 2 3 2 1 2 3 3 1 2 3 Shake Bond Types 1 1 1 1 2 1 1 1 3 1 1 1 Special Bond Counts 1 2 0 0 2 1 1 0 3 1 1 0 Special Bonds 1 2 3 2 1 3 3 1 2 ``` Wikipedia also has a nice article on [water models](https://en.wikipedia.org/wiki/Water_model)\_. ------------------------------------------------------------------------ ::: {#howto-tip3p} **(MacKerell)** MacKerell, Bashford, Bellott, Dunbrack, Evanseck, Field, Fischer, Gao, Guo, Ha, et al, J Phys Chem, 102, 3586 (1998). ::: ::: {#Jorgensen1} **(Jorgensen)** Jorgensen, Chandrasekhar, Madura, Impey, Klein, J Chem Phys, 79, 926 (1983). ::: ::: {#Price1} **(Price)** Price and Brooks, J Chem Phys, 121, 10096 (2004). :::