[Pw_forum] k point selection

[Cyrille Barreteau]

>>
>>
>> Thank you very much for the instruction on k point sampling,  I'll 
>> look into getting a copy of the Monkhorst Pack paper.  One more quick 
>> issue:  To save on computation time, does the automatic k point 
>> sampling for the scf calculation determine by itself which points 
>> comprise the irriducible brillouin zone? 
>
>
> try by yourself. run a calculation for, say, an fcc structure and see 
> whether or not you find two k points which are equivalent by any bubic 
> symmetry operation. (any operation of the cubic group can be seen as 
> the product of a parmutation of the cartesian coordinates - there are 
> seix such permutations - and the change of sign of any of the three 
> coordinates - there are 2^3=8 such operations - for a total of 48=6x8 
> symmetry operations)
>
The Monkhort Pack procedure generates a set of k points in the First 
Brillouin zone (in fact they are often outside the FBZ but can be
brought back into it by translations of reciprocal vectors). The code 
then determines by itself (thanks to the good work of the programmers:-) 
the
point that are inside the IBZ. Again they are not truly inside the IBZ 
(try to plot them in simple cases) but can be brought back inside
the IBZ by a succession of symmetries (and translations of reciprocal 
vectors).
The code also determines automatically the weight of each k-points 
according to their symmetries.

  cyrille