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