[gmx-users] k-space settings in GROMACS

[Anh Vo]

Hi everyone,

I'm trying to reconstruct in GROMACS some LAMMPS simulation to compare
between the two. I'm simulating a lipid bilayer system with 72 POPC lipids
and 9072 water molecules, as well as a single lipid system (1 POPC
molecule) and water only system (100 H2O molecules).

I try to use the same settings in GROMACS as in LAMMPS. However, in LAMMPS
I have *kspace_style* to define a long-range solver and *kspace_modify* to set
parameters used by the kspace solvers; but I'm not sure which command I
should use for similar settings in GROMACS. (I have read the manual and
searched online but haven't figured it out. Please accept my apology if
this seems to be an obvious question).

In details, these 2 commands in LAMMPS are:
*  - kspace_style    pppm  1e-5   *(pppm is P3M algorithm, 1.0e-5 means
that the RMS error will be a factor of 100,000 smaller than the reference
force)
*  - kspace_modify   diff  ad    *(*diff*  keyword specifies the
differentiation scheme used by the PPPM method to compute forces on
particles,  *ad*  keyword means approach uses only 1 FFT to transfer
information back to real space for a total of 2 FFTs per timestep).

Please help me to get similar settings in GROMACS (e.g. which command
should I use ?). Also, would it make a significant difference (e.g. in the
energy of the molecules, in the output pressure, etc.) if I use PME instead
of PPPM in GROMACS ?

Thank you very much for your help.

Best,
Anh Vo