bulk Si

[ramkrishna]

Dear Sir,
        I want to study the effect of strain on the band structure of bulk Silicon. Now, when I am stretching the cell (A or B or C in ATK-12.2) then in the band structure analysis it is showing only [G, Z], not the actual symmetry points. So, how can I see the strain effect on the bulk band structure? To check the proper strain effect on BULK Si, what should be the procedure?? 

Thanking you,
Ramkrishna   

[Anders Blom]

When you pull on the axes you also destroy the symmetry of the crystal. Therefore, the familiar symmetry points of the fcc lattice no longer apply.

ATK only has pre-defined symmetry points for the 14 Bravais lattices, so as soon as your system becomes represented as a UnitCell, there are no real symmetry points to choose from and that's why you get only G,Z (X and Y are also available; these are defined as X=kA/2, Y=kB/2, Z=kC/2 where ki are the reciprocal lattice unit vectors).

So, if you want to retain some symmetry - and hence have some access to the symmetry points - it will be better to convert the Si crystal to an orthorhombic crystal (or tetragonal), and then strain it by changing the lattice constants. Of course this means the calculation needs to be carried out in a supercell, so there will be some Brillouin zone folding.