Using lammps deform command to shear

Dear all,
I am using the lammps ‘deform’ command to do a shear simulation in the xz direction, and want to get stress-strain curve. But when xz reaches a maximum value (eg,50), it suddenly becomes negative (eg,-50), then increases to 0, and loops as this. (see the following figure) I also tested it with periodic and aperiodic boundary conditions,but the results are same.

The size of the box : Lx=103 Ly=96,Lz=209ang, is this related to the size of the box? What is the reason? And how can i get a reasonable response?

the deform command is : fix 1 all deform 1 xz erate 1e-4 remap x units


you have the “reasonable” behavior. please see the documentation of fix deform for details. there are plenty of explanations.