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
