On 4/27/20 7:43 PM, shakira shukoor wrote:
Hi
As far as I know tip3p water model is modelled to use in combination with
CHARMM force field. However there is nothing wrong in using TIP3P in
combination with GROMOS force field. And u will have both the bonded and
non bonded parameters of that specific water model in tip3p,itp file
itself. You don't have to get it from the force field. Instead you have to
add this itp file to the defined topology file you are giving.

GROMOS force fields were parametrized for use with SPC. As far as I know, no one has demonstrated that the use of TIP3P with GROMOS is valid.

-Justin

On Tue, Apr 28, 2020 at 4:29 AM Wei-Tse Hsu <weitse....@colorado.edu> wrote:

Dear gmx users,
I prepared a topology using Open Forcefiled for my system. To make GROMACS
able to recognize the water molecules and the ions to be added, I need to
include itp files (such as tip3p.itp, spc.itp, ions.itp, etc.) in my
topology file (.top file). I was planning to use GROMOS54a7 with TIP3P
water model, so I add the following lines to my topology file:

; Include water topology
#include "gromos54a7.ff/tip3p.itp"

In gromos54a7.ff, there is indeed a tip3p.itp file. However, getting the
error of " Atomtype OWT3 not found", I later found that OWT3 was not
defined in ffnonbonded.itp. I also tried pdb2gmx command using other system
and chose gromos54a7 force field, but there is no option for selecting
TIP3P water model. Therefore, I wonder if TIP3P water model is actually not
available in GROMOS54a7 force field even if there is a tip3p.itp in
gromos54a7.ff. I might just use SPC water model instead, but I want to make
sure that my understanding is correct. Thank you!

Best,
Wei-Tse
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