Question about fix_addforce command

To all lammps user.
I try to use fix_addforce command to apply a tensile stress to my specimen.
I
I use SI unit, so the force unit is newton.
The description of “fix_addforce” is Add fx,fy,fz to the corresponding component of force for each atom in the group.
If I want to calculate the stress I applied to each atom, the equation P=F/A what is the area value I should use? Area of single atom or area of wall ?

Thanks for your help

Regards
Wei-Jie Huang

To all lammps user.
I try to use fix_addforce command to apply a tensile stress to my specimen.
I
I use SI unit, so the force unit is newton.
The description of "fix_addforce" is Add fx,fy,fz to the corresponding
component of force for each atom in the group.
If I want to calculate the stress I applied to each atom, the equation P=F/A
what is the area value I should use? Area of single atom or area of wall ?

that depends on what you use for F, the total force or the force per atom.