energy correction term in ewald (PPPM) algorithm

Dear all,

1.When the net charge of my simulation system is not zero, the ewald (PPPM) algorithms will act as if the simulation cell is
surrounded by an evenly distributed countercharge and thus neutralized. Besides, I find that a correction to the system energy is
executed by LAMMPS (In page 327 of the LAMMPS manual (compute group/group command), it says that “However, one can
assume the net charge of the system is neutralized by a uniform background plasma, and a correction to the system energy can
be applied to reduce artifacts. This correction term does not affect the force calculation and will be zero if one or both of the groups
are charge neutral. This energy correction term is the same as that included in the regular Ewald and PPPM routines.”
I have used the compute group/group command to check whether the correction term is added. I found that the energy is
different, but the force is the same, if the boundary keyword is set to yes and no. So I want to know whether this energy
correction is included into the PPPM method during the MD simulation or it just work when the compute group/group command is used. What is the evidence that I can use to convince others?

Best regards

Zhang Chao

Stan can answer this.

Steve