Stress control in a plate.

Dear Lammps users

I am doing uniaxial tension on a metal plate (pps, 10x10x10 lattice parameters) at 0.01K. I can use fix deform to apply strain in x direction, atoms can move wherever they want along z direction.
To control pressure in y direction be zero I might use press/berendsen or fix npt. However, pyy varies with distance z from surface while the target pressure in press/berendsen or npt
is average values pyy(z) over the thickness. Do you think this is the uniaxial tension test? Or we can make a large model like pss with 10x2000x10 ?

Could you give some comments?

Thank you


If you deform slow enough and your system is uniform
in y, then I don't see why pyy won't equllibrate and become
uniform throughout the sample.