A question about ewald.cpp

Hi LAMMPS,

I am confused about the formula you use to calculate the force in kspace using ewald summation. I attach some references(the related formula in USERMAN is in pg. 159) about that (although they are in DPD, but kspace term should be the same). Firstly, the sign of the force should be negative. Secondly, the form of force expression is a little bit different from yours. You use preu=4*pi/volume, but they didn’t. Thanks a lot for your help.

Best,
Shiyi Qin

ct900296s.pdf (4.34 MB)

USRMAN.pdf (4.35 MB)