[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
AW: [ccp4bb]: SHLEX97 Q !
*** For details on how to be removed from this list visit the ***
*** CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html ***
The program SHELXL-93 calculated esds involving riding H-atom in a way
that was mathematically correct, assuming that the magnitude and
direction (but not position) of the X-H vector were exactly fixed; the
resulting esds thus depended on the combined scattering power of H and X
rather than just X. This gave rather small H-atom esds that confused
people, so I made the 97 version output zero esds for riding hydrogens. If
you want realistic esds for hydrogens you have to refine them freely (not
recommended for proteins)!
George Sheldrick
-----Ursprüngliche Nachricht-----
Von: S. Ravichandran [SMTP:ravi@cmb2.saha.ernet.in]
Gesendet am: Mittwoch, 1. März 2000 19:13
An: ccp4bb@dl.ac.uk
Betreff: [ccp4bb]: SHLEX97 Q !
*** For details on how to be removed from this list visit the ***
*** CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html ***
Hi All..
Though this is neither a CCP4 related question nor a protein
crystallography Q, I hope the small molecule crystallographer's who
have
used SHELX can help me out.
When refining the hydrogen atoms in the form of a 'riding' model,
how good
(or) reliable is the standard deviation values.. particularly for
bond
lengths (involivng hydrogens.. like C-H or N-H or O-H bonds) or the
e.s.d.'s for bond angles, involving hydrogen atoms.. say N-H-O or
C-H-O
etc..
I find that the SHELEX-93 gives a e.s.d. value for bond angles that
involve hydrogen atoms, whereas SHELX-97 don't give any!!
Hope I could convey my question properly??
Cheers,
Ravi.
=======================================================================
| S.Ravichandran e-mail:-
|
| Crystallography &
ravi@cmb2.saha.ernet.in |
| Molecular Biology Division, ravichu@hotmail.com
|
| Saha Institute of Nuclear Physics
|
| I/AF, Bidhan Nagar, Calcutta 700 064. FAX:-
|
| Calcutta - 700 064. INDIA. (91)(033)-337-4637
|
|
|
| URL: http://cmb2.saha.ernet.in/ravi.html
|
=======================================================================