[Pw_forum] Inconsistencies in the CELL_PARAMETERS - ibrav=5

Stefano de Gironcoli degironc at sissa.it
Thu Dec 23 17:28:15 CET 2010

Dear  Marino Vetuschi Zuccolini wrote:
> trigonal(r)
>                    ===================
>                    for these groups, the z-axis is chosen as the 3-fold axis, but the
>                    crystallographic vectors form a three-fold star around the z-axis,
>                    and the primitive cell is a simple rhombohedron. The crystallographic
>                    vectors are:
>                          v1 = a(tx,-ty,tz),   v2 = a(0,2ty,tz),   v3 = a(-tx,-ty,tz).
>                    where c=cos(alpha) is the cosine of the angle alpha between any pair
>                    of crystallographic vectors, tc, ty, tz are defined as
>                         tx=sqrt((1-c)/2), ty=sqrt((1-c)/6), tz=sqrt((1+2c)/3)

in order to extract c you are forgetting to divide v1 by a=|v1|.


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