super cell along specific direction

[Chaitanya Varma]

Dear sir,I am facing difficulty in understanding on how to generate supercell in a particular direction.i am interested in working with spinel ferrite NiFe2O4. it is fcc lattice with 56 atoms per unit cell. at present i am using quantum espresso for calculations.
Please tell me on how to generate 2 unit cells along 110 direction.thank you
 Chaitanya Varma M  

[Torbjörn Björkman]

The primitive lattice vectors normally chosen for the fcc lattice (as set up by cif2cell) are:

1/2 1/2 0
1/2 0 1/2
0 1/2 1/2

As you can see, the first of these are along your desired direction, so all you need to do is to extend the primitive unit cell along the first lattice vector:

cif2cell [spinelcif].cif --supercell=[2,1,1]

Hope this helps.
Torbjörn

[Chaitanya Varma]

thank you sir
i will try this.
regards
chaitanya varma