Doping a crystal

[TahirSiddiqui]

Hi, I'm a student and we've been given an assignment to dope a Cobalt Ferrite crystal with Antimony. Despite all my efforts I am unable to find any way to do it, could anyone please guide me as to how that can be achieved.?
Any help would be appreciated.

[zh]

First, check the literature to find out the crystal structure of cobalt ferrite for its lattice constants, space group, wyckoff position of atoms. See
http://arxiv.org/abs/1203.2088
 lattice parameter a = 8.385 ˚A 
cubic structure (F d − 3m)
Cations of Co and Fe occupy 8a and 16d special Wyckoffpositions at (1/2,1/2, 1/2) (1/8, 1/8, 1/8), respectively. Oxygen ions occupy the 32e positions at (x, x, x). The obtained value x = 0.2555(

Use the above information, you can build the structure of cobalt ferrite crystal.  The following is the conventional unit cell of this crystal, which is given in the POSCAR format of VASP.
Generated_by_spacegroup_Fd-3m:2
1.000000
      8.385000000000000      0.000000000000000      0.000000000000000
      0.000000000000000      8.385000000000000      0.000000000000000
      0.000000000000000      0.000000000000000      8.385000000000000
Co Fe O
     8     16     32
Direct
      0.125000000000000      0.125000000000000      0.125000000000000
      0.125000000000000      0.625000000000000      0.625000000000000
      0.625000000000000      0.125000000000000      0.625000000000000
      0.625000000000000      0.625000000000000      0.125000000000000
      0.875000000000000      0.875000000000000      0.875000000000000
      0.875000000000000      0.375000000000000      0.375000000000000
      0.375000000000000      0.875000000000000      0.375000000000000
      0.375000000000000      0.375000000000000      0.875000000000000
      0.500000000000000      0.500000000000000      0.500000000000000
      0.500000000000000      0.000000000000000      0.000000000000000
      0.000000000000000      0.500000000000000      0.000000000000000
      0.000000000000000      0.000000000000000      0.500000000000000
      0.500000000000000      0.750000000000000      0.750000000000000
      0.000000000000000      0.750000000000000      0.250000000000000
      0.500000000000000      0.250000000000000      0.250000000000000
      0.000000000000000      0.250000000000000      0.750000000000000
      0.250000000000000      0.750000000000000      0.000000000000000
      0.250000000000000      0.250000000000000      0.500000000000000
      0.750000000000000      0.750000000000000      0.500000000000000
      0.750000000000000      0.250000000000000      0.000000000000000
      0.250000000000000      0.500000000000000      0.250000000000000
      0.750000000000000      0.500000000000000      0.750000000000000
      0.250000000000000      0.000000000000000      0.750000000000000
      0.750000000000000      0.000000000000000      0.250000000000000
      0.255600000000000      0.255600000000000      0.255600000000000
      0.255600000000000      0.755600000000000      0.755600000000000
      0.755600000000000      0.255600000000000      0.755600000000000
      0.755600000000000      0.755600000000000      0.255600000000000
      0.744400000000000      0.744400000000000      0.744400000000000
      0.744400000000000      0.244400000000000      0.244400000000000
      0.244400000000000      0.744400000000000      0.244400000000000
      0.244400000000000      0.244400000000000      0.744400000000000
      0.744400000000000      0.505600000000000      0.505600000000000
      0.244400000000000      0.505600000000000      0.005600000000000
      0.744400000000000      0.005600000000000      0.005600000000000
      0.244400000000000      0.005600000000000      0.505600000000000
      0.255600000000000      0.994400000000000      0.994400000000000
      0.755600000000000      0.994400000000000      0.494400000000000
      0.255600000000000      0.494400000000000      0.494400000000000
      0.755600000000000      0.494400000000000      0.994400000000000
      0.494400000000000      0.994400000000000      0.755600000000000
      0.494400000000000      0.494400000000000      0.255600000000000
      0.994400000000000      0.994400000000000      0.255600000000000
      0.994400000000000      0.494400000000000      0.755600000000000
      0.005600000000000      0.505600000000000      0.244400000000000
      0.005600000000000      0.005600000000000      0.744400000000000
      0.505600000000000      0.505600000000000      0.744400000000000
      0.505600000000000      0.005600000000000      0.244400000000000
      0.005600000000000      0.744400000000000      0.005600000000000
      0.505600000000000      0.744400000000000      0.505600000000000
      0.005600000000000      0.244400000000000      0.505600000000000
      0.505600000000000      0.244400000000000      0.005600000000000
      0.494400000000000      0.255600000000000      0.494400000000000
      0.994400000000000      0.255600000000000      0.994400000000000
      0.494400000000000      0.755600000000000      0.994400000000000
      0.994400000000000      0.755600000000000      0.494400000000000
------------------------------
For the primitive unit cell:
Generated_by_spacegroup_Fd-3m:2
1.000000
      0.000000000000000      4.192500000000000      4.192500000000000
      4.192500000000000      0.000000000000000      4.192500000000000
      4.192500000000000      4.192500000000000      0.000000000000000
Co Fe O
     2      4      8
Direct
      0.125000000000000      0.125000000000000      0.125000000000000
      0.875000000000000      0.875000000000000      0.875000000000000
      0.500000000000000      0.500000000000000      0.500000000000000
      0.000000000000000      0.500000000000000      0.500000000000000
      0.500000000000000      0.500000000000000      0.000000000000000
      0.500000000000000      0.000000000000000      0.500000000000000
      0.255600000000000      0.255600000000000      0.255600000000000
      0.744400000000000      0.744400000000000      0.744400000000000
      0.266800000000000      0.744400000000000      0.744400000000000
      0.733200000000000      0.255600000000000      0.255600000000000
      0.255600000000000      0.255600000000000      0.733200000000000
      0.744400000000000      0.744400000000000      0.266800000000000
      0.744400000000000      0.266800000000000      0.744400000000000
      0.255600000000000      0.733200000000000      0.255600000000000

Depending on which kind of doping type of antimony you want to do, you may replace one of oxygen atoms with antimony atom, or add  one  antimony atom into the interestital site in the lattice.

One thing should be kept in mind, the doping concentration of antimony is other thing to be considered. That is number of antimony atoms and the size of simulated supercell.