Dear Steve and all lammpser,
According to the additions to the fix_addforce command carried out by Axel Kohlmeyer(10 Aug 2009), I modified the fix_efield.h and fix_efield.cpp (Please see the attachments), to allow this command to be applied only to atoms in a geometric region. More detailed description can be seen as following.
Hope this will help some lammps users.
fix_efield.cpp (3.37 KB)
fix_efield.h (991 Bytes)