But the edges for I and Hg are pretty far from CuKa (see attached). I am familiar with their being extra signal (white lines) very close to the peak, but not so far away....
JPK On Wed, Jun 6, 2012 at 2:15 PM, Bernhard Rupp (Hofkristallrat a.D.) <[email protected]> wrote: > There is also a relevant point from the physics of the absorption spectra - > the XANES white lines (near edge peaks higher than the continuum transition > or edge step) depend on the chemical environment of the anomalous atom in > terms of available unoccupied states (which n. b. is something entirely > different that the local neighbor environment/geometry which can be > backtransformed - although with quite some uncertainty - from the EXAFS > wiggles). > > Any argument about absolute f" peak values in absence of experimental > evidence (scan) might want to consider that..... > > Best, BR > > -----Original Message----- > From: CCP4 bulletin board [mailto:[email protected]] On Behalf Of Jacob > Keller > Sent: Wednesday, June 06, 2012 11:30 AM > To: [email protected] > Subject: Re: [ccp4bb] Fun Question - Is multiple isomorphous replacement an > obsolete technique? > > No offense taken (we all have our dour moments!), but grant me a sincere > question: the f" occupancy value would have been just as close at 11 as 5 if > the true value were 8, am I correct? In other words, do you imply by saying > "doing well" that you got as *much* as 5, or that you got as *close* as 5? I > am just trying to see whether I understand these things correctly. > > Jacob > > > > On Wed, Jun 6, 2012 at 12:21 PM, Gerard Bricogne <[email protected]> > wrote: >> Dear Jacob and all, >> >> I realise that my last statement sounds awfully dour and >> dismissive, in a way I really didn't intend. Especially as Stefan's >> original posting was a "Fun Question". >> >> Apologies to all for this over-the-top statement. I enjoyed a lot >> of the replies. >> >> >> With best wishes, >> >> Gerard. >> >> -- >> On Wed, Jun 06, 2012 at 06:09:33PM +0100, Gerard Bricogne wrote: >>> Dear Jacob, >>> >>> I thought that getting 5 for each iodine was doing pretty well, >>> given the circumstances - e.g. the noisy measurements, the primitive >>> software running on slow computers with tiny amounts of memory, etc. . >>> >>> In any case my main point, directed at the original poster, was >>> that reading the early Acta Cryst. issues ("RTFL") might be an >>> alternative and perhaps more enlightening way of getting a picture of >>> the evolution of phasing methods than finding some clever filter settings > in the RCSB ;-) . >>> >>> >>> With best wishes, >>> >>> Gerard. >>> >>> -- >>> On Wed, Jun 06, 2012 at 11:08:37AM -0500, Jacob Keller wrote: >>> > ...Even with such primitive techniques, I can remember an HgI4 >>> > > derivative in which you could safely refine the "anomalous > occupancies" >>> > > (i.e. f" values) for the iodine atoms of the beautiful planar >>> > > HgI3 anion to >>> > > 5 electrons. >>> > >>> > I am surprised--f"'s of I and Hg are supposed to be around 8 for >>> > CuKa (or maybe you weren't using CuKa)? >>> > >>> > JPK >>> > >>> > >>> > -- >>> > ******************************************* >>> > Jacob Pearson Keller >>> > Northwestern University >>> > Medical Scientist Training Program >>> > email: [email protected] >>> > ******************************************* >> >> -- >> >> =============================================================== >> * * >> * Gerard Bricogne [email protected] * >> * * >> * Global Phasing Ltd. * >> * Sheraton House, Castle Park Tel: +44-(0)1223-353033 * >> * Cambridge CB3 0AX, UK Fax: +44-(0)1223-366889 * >> * * >> =============================================================== > > > > -- > ******************************************* > Jacob Pearson Keller > Northwestern University > Medical Scientist Training Program > email: [email protected] > ******************************************* > -- ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program email: [email protected] *******************************************
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