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|. stefano
