# [lammps-users] tip3p water model

Hi there,

I am trying to use the tip3p model to simulate water. I tried both sets of tip3p parameters
as provided by:
http://lammps.sandia.gov/doc/Section_howto.html#4_7
By fix langevin at 298K and fix press/berendsen at 1 at, I got a density of 0.955 g/cm^3
for the first set of parameters, while 1.051 g/cm^3 for the second set of parameters.
I tried to reset epsilon for O-O in the second set of parameters to 0.152, and it will
give a density of 0.972 +/- 0.003 g/cm^3.

I am therefore wondering if the epsilon for O-O in the second set of parameter is a typo
of 0.152 ?

Thanks.

Lingti

2008/6/23 LT Kong <konzernlam@…24…>:

Hi there,

I am trying to use the tip3p model to simulate water. I tried both sets of tip3p parameters
as provided by:
http://lammps.sandia.gov/doc/Section_howto.html#4_7
By fix langevin at 298K and fix press/berendsen at 1 at, I got a density of 0.955 g/cm^3
for the first set of parameters, while 1.051 g/cm^3 for the second set of parameters.
I tried to reset epsilon for O-O in the second set of parameters to 0.152, and it will
give a density of 0.972 +/- 0.003 g/cm^3.

I am therefore wondering if the epsilon for O-O in the second set of parameter is a typo
of 0.152 ?

LT:

If you take the A and C values given in Jorgensen et al. [J Chem Phys, 79, 926 (1983)] for the TIP3P models (A = 582000, C = 595), and use them to solve for epsilon and sigma (A = 4 epsilon sigma^12, C = 4 epsilon sigma^6), then you get epsilon = 0.152073. So the values listed are correct.

There are some issues with TIP3P water (for instance, short-range forces were cutoff at < 8 A) which makes it not the best choice out there; you’re usually better off going with SPC/E or TIP4P instead.

–AEI