[gmx-users] tip3p

[Chetan Mahajan]

Hi All

I have tip3p water potential parameters from 3 different sources and they
differ quite substantially. I tried finding answer on the web or manual,
but no success.
Following lists all the three sources and bond potential force constant
(kb) value, in bracket as an example of how values differ in all the three
sources.

1. From the article: Neria, E.; Fischer, S.; Karplus, M. J. Chem. Phys.
1996, 105, 1902. (kb= 450 kcal/(mol.A02)), where A0 is angstrom. ( in
Gromacs units,
kb=188280 kcal/(mol.A02))

2. From tip3p files in forcefield directories in
gromacs/4.6.3/share/gromacs/top
(502416.0 kJ/(mol.nm2)

3. That used by acpype tool while converting amber input files to gromacs
input files.( 462750.4 kJ/(mol.nm2))

2 and 3 force constant units should conform to Gromacs, so kJ and nm.

It's very confusing, surprising and disappointing why these three values
differ so much. What is the correct value and why? I really appreciate your
response.

Thanks
Chetan