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Special positions

Boaz Shaanan..Biological Chemistry..The Hebrew University of Jerusalem...Israel BOAZSH at vms.huji.ac.il
Fri Feb 16 07:59:05 EST 1996

Dear Axel,

 In response to your reply about the special positions: how exact is 'exactly
on a special position' ? would 0.000, 0.000. 0.501 be considered exactly on
0,0,1/2 ? I presume not. Well, my experience is that there is a drift during
consecutive cycles of Xplor, maybe due to accumulation of rounding errors
(??). A few  cycles ago I put a water molecule on the 2-fold in 0,0.019,0.500
(sg C2), orthogonalized and  refined along. Now it's in 0.000, 0.019, 0.501.
Should I worry and reset it ?  If so, how often should this be checked ? Is it
because  the y coord is undetermined in this case, so Xplor doesn't think
it's really a  special position (unlikely) ?



 Boaz Shaanan                         . Phone: (972)2-658-5241/5411       *
 Dept. of Biological Chemistry        . Fax: (972)2-658-6448 or 666-804   *
 The Institute of Life Sciences       .                                   *
 The Hebrew University of Jerusalem   . E-mail: boazsh at vms.huji.ac.il     *
 Givat-Ram, Jerusalem 91904, ISRAEL   .                                   *

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