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SHELX C/D/E: Difference between revisions
→how to find out if a molecular replacement solution is correct or wrong
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The switch -e may be used to extrapolate the data to the specified resolution (the '''''free lunch algorithm'''''), based closely on work by the Bari group (Caliandro ''et al''., ''Acta Crystallogr''. (2005) '''D61''', 556-565) and independently implemented in the program [[Acorn]] (Yao ''et al''., (2005) ''Acta Crystallogr''. '''D61''', 1465-1475): -e1.0 can produce spectacular results when applied to data collected to 1.6 to 2.0 Å, but since a large number of cycles is required (-m400) and the 'contrast' and 'connectivity' become unreliable (the pseudo-free CC is the only reliable map quality indicator when the FLA is used), it may be best to establish the substructure enantiomorph and solvent content without -e first. The default setting when -e is not specified is to fill in missing low and medium resolution data but not to extrapolate to higher resolution than actually measured (to switch off this filling in, use -e999). The resolution requirements for the FLA still need to be explored, but so far there have been no reports of it causing a deterioration in map quality, and in a few cases the mean phase error was reduced by as much as 30º relative to density modification without it.<br> | The switch -e may be used to extrapolate the data to the specified resolution (the '''''free lunch algorithm'''''), based closely on work by the Bari group (Caliandro ''et al''., ''Acta Crystallogr''. (2005) '''D61''', 556-565) and independently implemented in the program [[Acorn]] (Yao ''et al''., (2005) ''Acta Crystallogr''. '''D61''', 1465-1475): -e1.0 can produce spectacular results when applied to data collected to 1.6 to 2.0 Å, but since a large number of cycles is required (-m400) and the 'contrast' and 'connectivity' become unreliable (the pseudo-free CC is the only reliable map quality indicator when the FLA is used), it may be best to establish the substructure enantiomorph and solvent content without -e first. The default setting when -e is not specified is to fill in missing low and medium resolution data but not to extrapolate to higher resolution than actually measured (to switch off this filling in, use -e999). The resolution requirements for the FLA still need to be explored, but so far there have been no reports of it causing a deterioration in map quality, and in a few cases the mean phase error was reduced by as much as 30º relative to density modification without it.<br> | ||
=== | === How to find out if a molecular replacement solution is correct or wrong === | ||
From a [https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind1111&L=ccp4bb&F=&S=&P=41951 November 2011 posting of George Sheldrick on CCP4BB]: We have unintentionally discovered a very simple way of telling whether | From a [https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind1111&L=ccp4bb&F=&S=&P=41951 November 2011 posting of George Sheldrick on CCP4BB]: We have unintentionally discovered a very simple way of telling whether | ||