[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
|
	
=======================================================================