Symmetry is the Crystallographer's first love, but periodicity is more important in deciding to call a structure 2D or 3D. Powder diffraction in particular showed that symmetry is ephemeral in many materials, whose symmetry is lowered when they are cooled. This symmetry is just the consequence of averaging over time and space. Yet we remain fascinated by symmetry, sometimes imposing it on Nature when it has no physical consequences.
Great to have a little philosophy to go with the Christmas pudding. Thanks Mathew. ________________________________ Dr Alan Hewat, NeutronOptics Grenoble, FRANCE (from phone) alan.he...@neutronoptics.com +33.476984168 VAT:FR79499450856 http://NeutronOptics.com/hewat _______________________________ On Sun, 25 Dec 2022, 01:16 Matthew Rowles, <rowle...@gmail.com> wrote: > I didn't even know of the existence of the frieze, rod, and layer groups > until I read this comment. > > So, I guess it's working? > > On Sat, 24 Dec 2022, 22:49 Leopoldo Suescun, <leopo...@fq.edu.uy> wrote: > >> Hi all, >> >> Thank you Matt for bringing up this issue. >> >> Massimo Nespolo has been fighting for the correct description of >> structures, specially focusing on symmetry and proper terminology, for >> years (see his many articles on the misuse of lattice, sublattice, >> superlattice, etc). >> >> He has, as well, been educating crystallographers of all ages in symmetry >> concepts and use through IUCr's MaThCryst Commision and Internationa School >> on Fundamental Crystallograpy courses around the world. >> >> He'll probably be remembered by many as a Dick Marsh of symmetry. >> >> I guess it is the task of all us, crystallographers, to promote the >> correct use of terminology related to crystal structures, as suggested by >> IUCr conventions included in IUCr Dictionary and modern literature. >> https://dictionary.iucr.org/Main_Page >> >> Best wishes for all of you that, in a way or another have this as a >> special week in your calendars, and Happy New Year for all. >> >> Leo >> >> El sáb, 24 de dic. de 2022 05:01, Matthew Rowles <rowle...@gmail.com> >> escribió: >> >>> Hi all >>> >>> I think this is the one >>> >>> https://scripts.iucr.org/cgi-bin/paper?S1600576721001606 >>> >>> Matthew >>> >>> On Fri, 23 Dec 2022, 10:00 Matthew Rowles, <rowle...@gmail.com> wrote: >>> >>>> This might be it, but the link is to the iucr homepage: >>>> >>>> Google: "letter to the editor" two-dimensional "layer groups" graphene >>>> iucr >>>> >>>> [image: image.png] >>>> >>>> >>>> >>>> >>>> On Fri, 23 Dec 2022 at 09:53, Matthew Rowles <rowle...@gmail.com> >>>> wrote: >>>> >>>>> Hi all >>>>> >>>>> A while ago (months, years??) I recall reading an editorial or letter >>>>> to the editor about materials being referred to as "2D", and how they're >>>>> actually 3D, and just periodic in the plane, and should be referred to as >>>>> 2P and a relevant layer group. >>>>> >>>>> Does anyone recall such a thing? >>>>> >>>>> >>>>> Thanks >>>>> >>>>> Matthew >>>>> >>>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>> Please do NOT attach files to the whole list >>> <alan.he...@neutronoptics.com> >>> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body >>> text >>> The Rietveld_L list archive is on >>> http://www.mail-archive.com/rietveld_l@ill.fr/ >>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>> >>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > Please do NOT attach files to the whole list <alan.he...@neutronoptics.com > > > Send commands to <lists...@ill.fr> eg: HELP as the subject with no body > text > The Rietveld_L list archive is on > http://www.mail-archive.com/rietveld_l@ill.fr/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > >
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
