Varying solvent mass

GROMACS version:
GROMACS modification: Yes/No
The solvent viscosity can be varied by changing the solvent mass. This can be done by varying parameters in the forcefield. I am trying to vary the viscosity of water molecules. What files in forcefield folder should one vary? I tried adding a separate column next to the forcefield, but it seems to not work. The atom names are mentioned in other .itp folders such as atomtypes.atp and ffnonbodend.itp.

Modiefied TIP3P.itp file:
[ moleculetype ]
; molname nrexcl

[ atoms ]
; id at type res nr residu name at name cg nr charge
#ifdef _FF_CHARMM
1 OT 1 SOL OW 1 -0.834 16.0
2 HT 1 SOL HW1 1 0.417 1.0
3 HT 1 SOL HW2 1 0.417 1.0

Masses of OT is defined as 15.99 in ffnonbonded.itp and atomtypes.atp. Should the masses be varied there too for varying the mass in total?

As far as I understand you want to change the mass of water atoms and run a simulation using the new mass.
Changing the mass in the topology file should be enough. Then one generarates the tpr file for the new setting.
To test if it works, I suggest to change the OT mass of larger amount than 0.01 uma.
In alternative, you try to change the value in ffnonbonded.itp (but may be better if mass values are not defined in topology ).

Hi Alevilla,
Thank you for your suggestions, I will give them a try.