Dear ccp4 users
a question about the recovering of true intensities from merohedral
twinned crystal. Providing alpha and the twin operator one should be able to
recover the
intensities from the formulas:
I(h1) = (1-α)Iobs(h1)-αIobs(h2)/(1-2α)
I(h2) = -αIobs(h1)+(1+α)Iobs(h2)/(1-2α)
as stated in many papers and books*.
However I was wondering about the uncertainties associated to these
measurements, I
mean: for all physical observable an uncertainty should be given.
Hence, what is the uncertainty associated to a perfect merohedrally twinned
crystal
(alpha=0.5)? It is clear that in this case we drop in a singular value of the
above
formulas.
Please, let me know your hints or your concerns on the matter. Probably there
is
something that it is not so clear to me.
Thanks in advance
Fulvio
ref. **(C. Giacovazzo, H. L. Monaco, G. Artioli, D. Viterbo, M. Milaneso, G.
Ferraris, G.
Gilli, P. Gilli, G. Zanotti and M. Catti. Fundamentals of Crystallography, 3rd
edition. IUCr
Texts on Crystallography No. 15, IUCr/Oxford University Press, 2011; Chandra,
N.,
Acharya, K. R., Moody, P. C. (1999). /Acta Cryst./ *D*55. 1750-1758)
--
Fulvio Saccoccia, PhD
Dept. of Biochemical Sciences "A. Rossi Fanelli"
Sapienza University of Rome
Tel. +39 0649910556
