Re: high symmetry points of diamond vs FCC

On Fri, 21 Jul 2006, #TEH LAY KUAN# wrote:
> Would like to check whether is there any difference in the coordinates 
> of the high symmetry points between a diamond lattice and a FCC lattice

No, the irreducible Brillouin zones are the same.
? 
> Eg. for diamond lattice, L point is given as (0 0.5 0) in MPB tutorial; 
> however, for FCC, L point is given as (0.5 0.5 0.5) from literature 
> (Kittel Solid state Physics book).

Two things to remember:

1) first, the k points in MPB are given in the reciprocal basis, not in 
cartesian coordinates, as described in the manual.

2) second, there are many equivalent rotations of the high-symmetry points 
(for example, there are eight equivalent L points).

> Another question I have is the radius of the spheres used. In the MPB 
> tutorial on diamond lattice, r is 0.25. So, if I were to compute the 
> band diagram for an opal (FCC) structure, the radius r should be 0.25 or 
> 0.35355 (i.e. sqrt2*0.25)?

The radius is completely arbitrary and has nothing to do with the lattice 
per se.  However, for an opal structure the spheres are usually tangent, 
and that's what you get for (* (sqrt 2) 0.25).

Steven