All right, the fourth time is a charm: The full tetragonal unit cell of beta-tin has four atoms in it.
However, the primitive body-centered unit cell as two atoms in it. You may want to look up the beta-tin structure, e.g. http://cst-www.nrl.navy.mil/lattice/struk/a5.html and see how you can construct the full tetragonal cell with four atoms from the primitive body-centered tetragonal unit cell containing two atoms. Understand this and you'll understand the origin of your 6/12 problem. On 01/04/2012 03:48 AM, bhabya sahoo wrote: > i want the phonon dispersion curve for beta tin structure > so i gave the positions of atoms as primitive tetragonal structure > having coordinates > 0 0 0, .5 0 .25 , .5 .5 .5, 0 .5 .75 like 4a whychoff positions (c/a=.546) > so no of atoms is 4 in the unit cell so in phonon there will be 12 branches > but i have seen 6 branches so how can i put my primitive tetragonal > structure having two atoms in unitcell > or in other way how can i give the input for beta tin structure -- Michael J. Mehl Head, Center for Computational Materials Science Naval Research Laboratory Code 6390 Washington DC
