[Pw_forum] sorry for the above bug letter

[Paolo Giannozzi]

On Thursday 01 September 2005 09:37, XiaoSong Du wrote:

> what i can't understand is the meaning of the 4 q-points in the star.
>                Number of q in the star =    4
>      List of q in the star:
>           1  -0.250000000  -0.250000000   0.250000000
>           2   0.250000000   0.250000000   0.250000000
>           3   0.250000000  -0.250000000  -0.250000000
>           4  -0.250000000   0.250000000  -0.250000000
>      In addition there is the -q list:
>           1 0.250000000 0.250000000-0.250000000
>           2-0.250000000-0.250000000-0.250000000
>           3-0.250000000 0.250000000 0.250000000
>           4 0.250000000-0.250000000 0.250000000

the code uses a rather complex symmetrization, involving the
response to several displacement patterns that transform into 
each other. As a result one gets the dynamical matrix at all the 
q-vectors that belong to the same star. There are 8 vectors 
in the star of <1/4, 1/4, 1/4> for cubic materials, and the results 
for -q and q are the same because of time reversal symmetry.

> By the way in the example I find the inputfile of non-scf and phonon
> calculation of GaAs describing k-space sampling is wrong, which 
> should be a 444 M_P sampling instead of the 2 point. Am I right? 

it is a 444 Monkhorst-Pack sampling, without displacement (the
grid has to include q=0)

Paolo

-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513 
Piazza dei Cavalieri 7      I-56126 Pisa, Italy