How to relax metallic nanowires?

Hi Lammps Users:
I’m a freshman to MD, now I want to do some simulation about Cu nanowires. The first problem for me is how to relax a circular nanowires with fcc lattice.In my scripts, r and l represents the radius and length respectively, T represents the temperature.I’d like to construct nanowire in two different ways.
1.My first method to construct the nanowire is the nanowire is the whole box, like:

boundary s s p

region wire cylinder z $r $r $r 0 $l
create_box1 wire
create_atoms 1 region wire
I tried nvt relaxation, the commands is:
fix nvt_relax2 all nvt temp $T 1000 0.005 drag 0.2
fix nvt_relax4 all nvt temp 1000 $T 0.005 drag 0.2
But there is large tensile force or something cause the nanowire to warp. This happened with both Cu Mishin eam potential or Cu zhou eam potential, and the range of r is from 5 lattice constants to 30 lattice constants. I don’t know why this happened and whether the nvt relaxation method is proper.
I also tried npt relaxatio

My question may be a long one, thanks for your time!

you can try the minimize command