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] *******************************************
