As Tassos correctly says, the 'usual phasing statistics' are utterly irrelevant to phasing a structure with SHELXE. SHELXC/D/E adopt a minimalist approach, and input and calculate only what is needed to get a map that is good enough to interpret. For example, in order to calculate RCullis one would need to know the exact composition of the crystal and the f" values of all the elements present, information that may well not yet be known correctly. Rather than printing a value that should probably be changed later and is not used in the phase determination, I prefer not to calculate it at all.
By chance a paper "Experimental phasing with SHELXC/D/E: combining chain tracing with density modification" has just appeared as Open Access: Acta Cryst. D66 (2010) 479-485. George Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-3021 or -3068 Fax. +49-551-39-22582 On Mon, 12 Apr 2010, Dirk Kostrewa wrote: > Hi Tassos, > > my personal opinion is, that I would like to see the usual phasing statistics. > At least to me, they provide hints how well the structure was determined, > analogous to the R-factor/Free-R-factor providing hints how well the structure > was refined. > > It would be good if SHELXE would print out those statistics before any density > modification. > > Best regards, > > Dirk. > > Am 12.04.10 13:10, schrieb Anastassis Perrakis: > > Hi - > > > > A year or so ago, I have asked as a referee somebody to provide for a paper > > the statistics for their heavy atom derivative dataset, > > and for the phasing statistics. For some good reasons, they were unable to > > do that, and they (politely) asked me > > 'what would it change if you knew these, isn't the structure we present > > impeccable?'. Well, I think they were right. > > Their structure was surely correct, surely high quality. After that incident > > and giving it some thought, > > I fail to see why should one report e.g. PP or Rcullis, or why will I care > > what they were if the structure has a convincing Rfree and is properly > > validated. > > If someone wants to cheat at the end of the day, its easy to provide two > > numbers, but its hard to provide a good validated model that agrees with the > > data. > > (and, yes, you can also make up the data, but we have been there, haven't > > we?!?) > > > > So, my question to that referee, likely being a ccp4bb aficionado that is > > reading this email, or to anyone else really, is: > > > > "What would it help to judge the quality of the structure or the paper if > > you know PP, Rcullis and FOM?" > > > > Best - > > > > A. > > > > PS Especially since you used SHELXE for phasing these statistics are utterly > > irrelevant, and possibly you could advice the referee to read a bit about > > how SHELXE works ... or go to one of the nice courses that George teaches > > ... > > > > On Apr 12, 2010, at 10:37, Eleanor Dodson wrote: > > > > > You can feed the SHELX sites into phaser_er or CRANK both of which will > > > give this sort of information. > > > > > > Or mlphare if you know how to set it up.. > > > > > > Eleanor > > > > > > > > > Harmer, Nicholas wrote: > > > > Dear CCP4ers, > > > > > > > > I've been asked by a referee to provide the phasing statistics for a SAD > > > > dataset that I used to solve a recent structure. Whilst I have been able > > > > to find a figure-of-merit for the data after phasing, I can't work out > > > > how to get any other statistics (e.g. phasing power or an equivalent or > > > > Rcullis). Does anyone know a good route to obtaining useful statistics > > > > to put in the paper for SAD data? > > > > > > > > The structure solution was carried out using SHELX C/D/E and then > > > > ARP/wARP. > > > > > > > > Thanks in advance, > > > > > > > > Nic Harmer > > > > > > > > ===================== > > > > Dr. Nic Harmer > > > > School of Biosciences > > > > University of Exeter > > > > tel: +44 1392 725179 > > > > > > > > *P** **please don't print this e-mail unless you really need to* > > Anastassis (Tassos) Perrakis, Principal Investigator / Staff Member > > Department of Biochemistry (B8) > > Netherlands Cancer Institute, > > Dept. B8, 1066 CX Amsterdam, The Netherlands > > Tel: +31 20 512 1951 Fax: +31 20 512 1954 Mobile / SMS: +31 6 28 597791 > > > > > > > > > > -- > > ******************************************************* > Dirk Kostrewa > Gene Center, A 5.07 > Ludwig-Maximilians-University > Feodor-Lynen-Str. 25 > 81377 Munich > Germany > Phone: +49-89-2180-76845 > Fax: +49-89-2180-76999 > E-mail: kostr...@genzentrum.lmu.de > WWW: www.genzentrum.lmu.de > ******************************************************* > >
