Questions about Hollow SiNW tensile test

Dear Lammps users,
I’m a lammps newbie. I do uniaxial tensile experiments on hollow-core silicon nanowires.
According to the paper I referenced, the larger the empty space, the more ductile properties should be.
However, necking does not appear well. I’m not sure why that is. I ask for help.
I attach my input file below.
Thank you

hollow_core_40.lmp (2.7 KB)