Dear Magnus,

Make sure you are using the latest version of PLATON - unix version is
usually the most up to date. I think it is 17/07/08 at the moment.

Best to email Ton Spek. I have had problems before with addsym. It may add
lines not compatible with Shelx-97 (A lot of PLATON was written with
Shelx-86 in mind) and therefore could provide unexpected results.

Proceed with the latest UNIX version before speaking to Ton. It can be
installed onto Mac OS X as well. There are instructions how to do this.

The windows version tends to lag behind, it is dependent on others to
provide the latest version.

Regards
William




> Hi!
>
>
>
> I was getting some unexpected results from Addsym (Platon version 230608)
> so
> I ran some tests to try to clear things up. Now I’m confused to the point
> where I need help!
>
>
>
> The test structure I have used is:
>
> Space group P-1
>
> a = 3.5 Å  b = 12.3 Å  c = 4.5  alpha = beta = gamma = 90 deg
>
>
>
> Al1 in    0.06   0.85   0.75
>
> Al2 in    0.49   0.33   0.77
>
>
>
> This is pseudo-Cmcm symmetry. True Cmcm positions (0 x ¾ , ½ x ¾) are only
> 0.24 Å away.
>
>
>
> There are three points that are about to drive me nuts:
>
>
>
> 1) Addsym suggests P21/m instead of Cmcm. It has no effect to increase the
> criteria parameters d1, d2 and d3 from the default 0.25 Å to 0.5 Å.
>
>
>
> 2) If I move the structure somewhat closer to Cmcm symmetry by putting Al1
> in, say, 0.03   0.85   0.75, I get no new space group suggestion at all!
> Addsym produces some lines that say
>
>
>
> “E: SYMM TRANSLATION n/a: 0.958 .500 0”
>
>
>
> during the run and writes
>
>
>
> “Higher (pseudo)symmetry not compatible,(current symmetry retained)”
>
>
>
> in the lis-file.
>
>
>
> 3) When I move the atoms very close to the Cmcm positions, e.g.
>
>
>
> Al1 in    0.01   0.84   0.75
>
> Al2 in    0.49   0.33   0.74
>
>
>
> then Addsym suggests Cmcm if I launch it from the command line. If I use
> the
> graphical interface, it suggests Pmma instead. That happens even if I
> place
> the atoms in ideal Cmcm positions.
>
>
>
> Are these things user errors or bugs? If they are user errors I would be
> very grateful if anybody could explain what I’m doing wrong or point out
> something I can read. I’m aware of the Platon/Addsym resources on the
> ccp14,
> but I didn’t find anything there that helped me.
>
>
>
> I see on the Platon web page that the newest version should be from July
> 13
> 2008, but the version I can download is still from June.
>
>
>
> Best wishes,
>
> Magnus
>
>


-- 
William Bisson

Administrator and Webmaster
http://www.ccp14.ac.uk
http://bca.chem.ucl.ac.uk


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