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Hi Qun Because the 3 axes in orthorhombic space groups are non-equivalent but in P212121 all are 2-fold screws, there are indeed 6 permutations for assigning the axes (unless of course 2 of those are excluded from consideration by some other information that you haven't mentioned). These are klh and lhk in addition to the ones you mention. For a reference see International Tables Vol A, chap. 2, p. 21. Normally the standard permutation is decided by the order of the magnitudes of the cell axis lengths, but presumably you are doing this because all 3 cell lengths are very nearly equal (within experimental error including possible non-isomorphism), otherwise what you are proposing wouldn't make sense. If for example only 2 of the cell lengths were nearly equal this would reduce the number of feasible possibilities to only 2 (e.g. hkl and hlk if a!=b=c). The minus signs in the matrix are required to maintain the same hand after transformation in the case that you have measured anomalous differences. Alternatively you could keep the indices all positive and change the sign of the delta-anoms in the cases where the permutation is non-cyclic (i.e. hlk, lkh and khl). If you have no anomalous data then it makes no difference whether you have the minus signs or not, by Friedel's law the amplitudes of hkl and -h-k-l are equal. HTH! -- Ian > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > Behalf Of Qun Wan > Sent: Tuesday, May 02, 2006 10:14 PM > To: [email protected] > Subject: [ccp4bb]: permute unit cell indices > > *** For details on how to be removed from this list visit the *** > *** CCP4 home page http://www.ccp4.ac.uk *** > > > Hi, > I Have a question about permuting crystal indices. When I compare two > crystal data sets to get crossR value to know how isomorphous they > are, I need to permute the indices of one of the crystal. Both of my > crystals have space group P212121. I was told to permute HKL to LKH, > HLK, and KHL. I do not have a clear mind the principle. For example, > by whole arrangement, there will be 6 possibilities for the > permutation. Why only four exist here? The second question is more > important: if I want to change from HKL to KHL, the new indices are > (0 -1 0 -1 0 0 0 0 -1), not (0 1 0 1 0 0 0 0 1). Why there > is minus sign in the indices? > > Could anyone recommend me one paper or book to read to solve > my puzzle? > > Your help is greatly appreciated! > > Disclaimer This communication is confidential and may contain privileged information intended solely for the named addressee(s). It may not be used or disclosed except for the purpose for which it has been sent. If you are not the intended recipient you must not review, use, disclose, copy, distribute or take any action in reliance upon it. If you have received this communication in error, please notify Astex Therapeutics Ltd by emailing [EMAIL PROTECTED] and destroy all copies of the message and any attached documents. Astex Therapeutics Ltd monitors, controls and protects all its messaging traffic in compliance with its corporate email policy. The Company accepts no liability or responsibility for any onward transmission or use of emails and attachments having left the Astex Therapeutics domain. Unless expressly stated, opinions in this message are those of the individual sender and not of Astex Therapeutics Ltd. The recipient should check this email and any attachments for the presence of computer viruses. Astex Therapeutics Ltd accepts no liability for damage caused by any virus transmitted by this email. E-mail is susceptible to data corruption, interception, unauthorized amendment, and tampering, Astex Therapeutics Ltd only send and receive e-mails on the basis that the Company is not liable for any such alteration or any consequences thereof.
