Dear Monica, if you are new to phasing I recommend you first use the ``standard'' values in shelx c/d/e, either using one of my tutorials or, even better, the GUI hkl2map, available at http://webapps.embl-hamburg.de/hkl2map/.
If your native data are about 2A or better, and your structure is a protein, shelxe should be able to trace a major part of it even from very poor starting phases, making it unnecessary to try the below hint. If you do, shelxd is steared by an input file containing various keywords. One is the SHEL command with the upper and lower resolution limit. If you prepare 26 input files (all with different names) and vary the second number in SHEL from 2.5 2.6 2.7 ... 5.0 you scan the different resolution cut-offs. However, shelxd has become less sensitive to the resolution cut-off, in particular in combination with auto-tracing in shelxe. The second part, Emin, refers to the keyword ESEL. Its default value is 1.5. If you lower the number to 1.2, say, shelxd uses more data for locating the substructure, but since this way you may also include noise, the exact number is difficult to tell in advance. Best wishes, Tim On 04/22/2014 10:13 AM, Monica Mittal wrote: > Dear all > > I am naive in phasing experiments. CAn anyone please guide how to do the > following: > > In a S-SAD for *SHELXD* searches, try various high-resolution cutoffs for > example 2.5 to 5 Å in steps of 0.1 Å. Based on these attempts, use a > high-resolution cutoff at for example 3.8 Å for substructure determination > with an *E* min value of for example 1.6 to search for X no. of protein > sulfur sites. > > Thanx in advance > Monica > -- Dr Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A
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