Re: [Ifeffit] non-standard space group P 21/n

Andrea, I was on a train without internet access much of yesterday. Happily, you got some useful feedback from others. The mailing list really is a good place to ask questions! From your original email, I get the sense that you are using the very old version of Atoms, which is written in Fortran and which was last worked on in 1998. While Wayne's advice is certainly correct and actionable, I am pretty confident that the current version of Atoms knows how to interpret the space group symbol P 21/n. At least, that symbol is in the database: https://github.com/bruceravel/demeter/blob/master/lib/Xray/Crystal/share/spa... For this sort of question, it is usually a good idea to post the actual crystal data (or a link to it) when you ask your question. That way, you can get a specific answer to your specific question, rather that the sort of generic, "you might try this..." sorts of answers you have gotten from Wayne, Robert, and myself. Hopefully, Wayne's impressive command of 3D geometry has gotten you over your hurdle! Cheers, B On 12/06/2014 03:44 AM, andrea.sanson@unipd.it wrote:

Dear Wayne,

thank you very much for your enlightening answer!

Best regards, Andrea

Dear Andrea,

To convert the atomic positions, use the following equations (starred positions are in the P21/c setting)

a* = c b* = b c* = a+b

To convert the unit cell,Â

A* = C B* = B C* = sqrt{[Ccos(90-beta)]^2+[A-Csin(90-beta)]^2} beta* = 90 - cos-1[Ccos(90-beta)/C*] where cos-1 is the inverse cosine function

If you have problems, please double check my geometry for converting the unit cell parameters.

Sincerely,

Wayne

On Fri, Dec 5, 2014 at 9:04 AM, wrote:

Dear Gordon,

thank you for your reply. I tried to use the space group P1, but the resulting local structure around the absorber atoms is completely different from that expected.

Andrea

HI Andrea,

My suggestion, if you know where all the atoms are in the unit cell, is to use

space group P1. It may be tedious and brute force in nature, but you won't have to worry about origin choices or non-standard space groups. You will still know

which atoms are equivalent and can pick an appropriate one as your target atom.

regards, Robert

On Fri, Dec 5, 2014 at 8:07 AM, Sanson Andrea wrote:

Dear all

does anyone know if is it possible to create with ATOMS the non-standard space group P 21/n ?

Space group keywords are listed at the atoms website http://iffwww.iff.kfa-juelich.de/icp/atoms/atoms.sgml-7.html#ss7.4 but no keyword for P 21/n group is available.

Thanks for any suggestion. Best regards, AS

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-- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS-II Building 535A Upton NY, 11973 Homepage: http://bruceravel.github.io/home/ Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/