On Sun, Aug 24, 2008 at 08:08:00PM +0100, Phil Evans wrote:
> As you say, the linear fit is only used to put data on a very rough
> absolute scale. This isn't necessary, but it doesn't hurt
It might be necessary after all for experimental phasing using heavy
atoms: you want to start refinement of the occupancies from something
not too far away. If your data is off by 1000 starting with values of
1.0 might be too bad for the minimizer to get anywhere.
This becomes especially tricky if you have poor data (low resolution
and/or quality), a poor initial heavy atom solution or no real idea of
the numbner of molecules per asymmetric unit (especially difficult for
large numbers).
Unfortunately you often have to deal with a combination or even all of
the above. But if you're lucky your resolution is so low that you
don't have to worry about the other things anway ;-)
So in general I think it is a good thing to do.
Cheers
Clemens
--
***************************************************************
* Clemens Vonrhein, Ph.D. vonrhein AT GlobalPhasing DOT com
*
* Global Phasing Ltd.
* Sheraton House, Castle Park
* Cambridge CB3 0AX, UK
*--------------------------------------------------------------
* BUSTER Development Group (http://www.globalphasing.com)
***************************************************************
|