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 Im 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 Im doing wrong or point out > something I can read. Im aware of the Platon/Addsym resources on the > ccp14, > but I didnt 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
