These are good learning events. .
And it doesn't make much third dimensional periodicity to make a layered material act as a bulk 3d material (see recent publications by Kate Putman), or at least from a powder diffraction point of view. On Sun, 25 Dec 2022, 12:40 Alan W Hewat, <alan.he...@neutronoptics.com> wrote: > 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/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
