[gmx-users] Exclude Coulomb interactions among certain atoms in SWM4 water molecule

[Sandipan Dutta]

Dear GMX users:

I am fairly new to gromacs. I am trying to simulate SWM4 water model. In
the model the electrostatic interactions between the Drude particle (DOH2)
and oxygen atom (OP) are excluded. I have created an index file index.ndx
that contains the numbers of the DOH2 and OP atoms. In the grompp.mdp file
I have used the energygrp_excl command to exclude the energies between the
groups. But when I run the grompp command:

grompp -maxwarn 3 -n index.ndx

I get the following error:

WARNING 1 [file grompp.mdp]:
  Can not exclude the lattice Coulomb energy between energy groups

Fatal error:
atoms 1 and 2 in charge group 1 of molecule type 'Other' are in different
energy groups

I have attached the grompp.mdp and the index.ndx files. Can someone please
help me with these?

Thanks a lot!!!

Sandipan Dutta
APCTP, South Korea