*** For details on how to be removed from this list visit the ***
*** CCP4 home page http://www.ccp4.ac.uk ***
It's actually very easy to refine the occupancy of a ligand in SHELXL!
All you need to do is to define a free variable to use as a common
occupancy for all the atoms of the ligand. If you are not already using
free variables, then this will be #2 (#1 is always the overall scale
factor) so set:
FVAR 1.0 0.5
to give it a starting value of 0.5 (not critical). Then change the
occupancy (usually 11 = fix at 1.0) to 21 (= 1.0 times free variable 2)
for each atom in the ligand. If it is a large ligand, you can override
the occupancies on the atom cards by including:
PART 0 21
before the first atom of the ligand and
PART 0 11
after the last. If your ligand has two conformations and the occupancies
add up to one, you can impose this by using PART 1 21 before the first
and PART 2 -21 before the second component (and PART 0 11 after them).
If the occupancies don't add up to one, just use two free variables. If
your ligand has more than two conformations, you can restrain the sum of
the free variables used as occupancies using a SUMP instruction. There
are many examples of occupancy refinement in the SHELX manual.
The flexible occupancy refinement (and refinement of twinned crystals)
is the SHELXL facility that we miss most when we have to refine with REFMAC.
George
michael nelson wrote:
From the responses,I believe my ligand has a low occupancy.
But technically, how do I refine the occupancy of the ligand? I'm using
shelxl at this moment, but it's a bit hard to refine its occupany in this
program.Anybody know how to do it?
Probably I should switch to CNS or Refmac5.
Many thanks anyway.
Mike
__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
--
Prof. George M. Sheldrick FRS
Dept. Structural Chemistry,
University of Goettingen,
Tammannstr. 4,
D37077 Goettingen, Germany
Tel. +49-551-39-3021 or -3068
Fax. +49-551-39-2582
