Twisting of nanotubes

Dear all,

I want to rotate the upper end of the carbon nanotube while keeping the bottom end fixed so that the CNT will twist in mid. I tried to do with the following input script but I failed to do so. My CNT is not twisting. Please help me.

Attachment: Input script and data file
eq.data (147.7 KB)
shearmodulus.in (2.3 KB)