[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:
> 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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