Dear LAMMPS developers,
Recently, I have a question about the calculation of long-ranged Coulomb interactions. As we known, the PPPM algorithm in Lammps software must be used in periodic systems. But in our simulations, the polyelectrolytes solutions confined in cylindrical pores are studied by means of Lammps. The cylindrical axis is along the z-direction and the periodic conditions are set. The x- and y-direction are confined walls, therefore, the periodic conditions seems to be unreasonable. But the long-ranged Coulomb interactions must be considered in polyelectrolytes solutions, and the PPPM algorithm is an effective method for handling the long-ranged interaction. What should we do to deal with this conflict?
Thank you very much.
Best wishes.
Hao
Dear LAMMPS developers,
Recently, I have a question about the calculation of long-ranged Coulomb
interactions. As we known, the PPPM algorithm in Lammps software must be
used in periodic systems. But in our simulations, the polyelectrolytes
solutions confined in cylindrical pores are studied by means of Lammps. The
cylindrical axis is along the z-direction and the periodic conditions are
set. The x- and y-direction are confined walls, therefore, the periodic
conditions seems to be unreasonable. But the long-ranged Coulomb
interactions must be considered in polyelectrolytes solutions, and the PPPM
algorithm is an effective method for handling the long-ranged interaction.
What should we do to deal with this conflict?
there are multiple possible approaches:
- you can just use fixed boundaries and a long cutoff and no kspace
(best for small systems)
- you can use pppm and periodic boundaries, but increase the box size
until the interaction between periodic images becomes small enough for
your purposes (requires careful testing. best used in combination with
the balance command).
- you can try using msm instead (can be much slower, if you require
high accuracy. again, requires careful testing)
axel.
As Axel indicates, kspace_style MSM allows for non-periodic in any
or all of the 3 dimensions.
Steve