Inducing Poiseuille flow with fix srd

Hi LAMMPS users and developers,

I am trying to simulate Poiseuille flow in a channel with SRD fluid as solvent by LAMMPS software. Here, I have edited the in.srd.pure example script provided by the software with fix wall/srd and fix addforce (or fix gravity).

fix 1 all srd 1 NULL 1.0 0.25 49894 collision slip inside ignore

fix 2 all enforce2d

fix 3 all addforce 0.0 0.02 0.0

#fix 3 all gravity 0.01 vector 0 1 0

fix 4 all wall/srd xlo EDGE xhi EDGE

However, I found the fix addforce or fix gravity did not work. Going through the LAMMPS Mailing List Archives, I came across the mailing list (, which suggests the SRD fix should be modified to introduce the force term. I have contacted with Mr. Bolintineanu but received no reply. I wonder if anyone has the modified version of fix_srd.cpp.

Best regards,

Su (1 KB)