Thanks very much for this interesting discussion. We should have that more often. Marius
> -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > 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 > ******************************************************************* > > > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.4.8 (Darwin) > > iEYEARECAAYFAkhj+MEACgkQlz6UVQtc2uw7FACguUgF1+XrN9xdRTcLLdShA/Eu > A2UAniYPecEAz5BJ/ljrQYymnGRK7Mor > =SItL > -----END PGP SIGNATURE----- Dr.habil. Marius Schmidt Asst. Professor University of Wisconsin-Milwaukee Department of Physics Room 454 1900 E. Kenwood Blvd. Milwaukee, WI 53211 phone: +1-414-229-4338 email: [EMAIL PROTECTED] http://users.physik.tu-muenchen.de/marius/
