band structure of silicene nanosheet

[Ashley.amanta@gmail.com]

Hi
I built a silicene nanosheet,the steps are as follow
1.open builder
2.from Add>from plugin >nanosheet
3.change carbon to si
4.set the bond lenght to equal 2.2286
5.Align unit cell vector C with chiral vector n=3,m=0
6.build
7.apply buckle with a depth of 0.44
I relaxed the structure,I want to calculate band structure,I know to calculate band structure I have to from Bulk tools open lattice parametere,and change lattice type to hexagonal and then center it,and analysis band structure around the K point,but when I change it to hexagonal,the structure from nanosheet change to single-dimensional,why?
And the band structure is as follow(I attached band structure)
Thank you

[lknife]

for the bandstructure of silicene, you can refer to this tutorial http://docs.quantumwise.com/tutorials/opening_a_band_gap/opening_a_band_gap.html