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Le 26 juin 08 à 18:49, Ethan Merritt a écrit :
On Thursday 26 June 2008 09:36:16 am Serge Cohen wrote:
Please some one tells me if I'm wrong ... but I though that indeed
one
is NOT supposed to measure anomalous difference from reflections h
and
h' if those are related by one of the symmetry operator of the point
group...
This statement is logically equivalent to what Patrick writes below.
You are agreeing with each other.
Indeed I was thinking of Bernie Santarsiero mail when sending this mail.
Bernie's mail was confusing my understanding. To quote the part I was
referring to :
Friedel pair is strictly F(hkl) and F(-h,-k,-l).
Bijvoet pair is F(h) and any mate that is symmetry-related to F(-
h), e.g.,
F(hkl) and F(-h,k,-l) in monoclinic.
That is in monoclinic (P 1 2 1, more precisely) , (h, k, l) and (-h,
k, -l) should have the same F ... (in a determinist's world)
Yes, but that is not an example of h and h'.
You mean that in P 1 2 1, h,k,l and -h,k-l are not strictly equivalent?
In the context of my message h and h' were defined as :
reflections h and
h' if those are related by one of the symmetry operator of the point
group
To come back to the initial mail :
b) A Friedel pair is any reflection h = -h including hR = -h, i.e.
including centric reflections.
I find this notation confusing since (I guess) the '=' does not mean
the same thing in both cases :
In the first case it means the pair (h, -h) (or more precisely what I
understand it means)
While the second really means "There is a R operator of the PG" such
that -h = Rh (if the first case had to be understood this way, the
only Friedel pair would be (0,0,0) ).
So if I try to put this definitions of terms as I understand them:
Friedel pair : (h, g)
"There is a operator R of the P.G." such that -Rh = g
Bijvoet pair : (h, g)
"There is a operator R of the P.G." such that -Rh = g
AND : "For all operator R of the P.G." : Rh != g
Hope I'm getting it right ... and I'm not adding to the overall
confusion ;-)
Serge.
*******************************************************************
Dr. Serge COHEN
GPG Key ID: 0B5CDAEC
N.K.I.
Department of Molecular Carcinogenesis (B8)
Plesmanlaan 121
1066 CX Amsterdam; NL
E-Mail: [EMAIL PROTECTED]
Tel : +31 20 512 2053
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