Pardon me for intruding, but if a substance is only 1 atom thick, is it not the case that its symmetry is reasonably given by one of the 17 plane groups, or alternatively by the layer group which simply inserts a mirror in the plane?
Robert Gould Tel. 0131 447 8513 or 0796 040 3872 On Fri, 30 Dec 2022 at 14:23, Mike Glazer <mike.gla...@physics.ox.ac.uk> wrote: > Since everything is made of atoms all materials are 3-dimensional. The > differences lie in the dimensionality of the periodicity, which can be > n-dimensional. In the case of graphene, you can consider it to be > 2-dimensional if you are willing to approximate atoms as having 0 > thickness, and then the symmetry would be given by one of the 17 plane > groups i.e. p6mm. But strictly speaking because everything contains atoms, > nothing really crystallises in one of the plane groups. > > The fact is that everything is 3 dimensional. Graphene is 3 dimensional, > in my view, because it exists in a 3-d space --- it has weight, it can be > held in your hand, you can see it, etc. So strictly speaking, if you > consider the size of atoms to be relevant, it should be listed as p6/mmm > layer symmetry. Otherwise you can approximate as 2-dimensional, so it is up > to you how far you want to approximate. In any case, all observed symmetry > in crystals results from averaging over space and time. > > Mike Glazer > > > > > > > > *From:* Radovan Cerny <radovan.ce...@unige.ch> > *Sent:* 30 December 2022 12:44 > *To:* Matthew Rowles <rowle...@gmail.com> > *Cc:* Mike Glazer <mike.gla...@physics.ox.ac.uk>; RIETVELD_L Distribution > List <rietveld_l@ill.fr> > *Subject:* RE: "2d materials don't exist" editorial?? > > > > Uff, I do not know who has written this page > > > > > https://en.wikipedia.org/wiki/Single-layer_materials#C:_graphene_and_graphyne > > > <https://en.wikipedia.org/wiki/Single-layer_materials#C:_graphene_and_graphyne> > > Single-layer materials - Wikipedia > <https://en.wikipedia.org/wiki/Single-layer_materials#C:_graphene_and_graphyne> > > In materials science, the term single-layer materials or 2D materials > refers to crystalline solids consisting of a single layer of atoms. These > materials are promising for some applications but remain the focus of > research. Single-layer materials derived from single elements generally > carry the -ene suffix in their names, e.g. graphene.Single-layer materials > that are compounds of two or more ... > > en.wikipedia.org > > > > > > but it was not Mike. Graphene is listed among 2D materials as well as > phosphorene (which I understand easily as its layer is not planar). > > > > Radovan > > > > Radovan Cerny > Laboratoire de Cristallographie > Université de Genève > 24, quai Ernest-Ansermet > CH-1211 Geneva 4, Switzerland > Phone : [+[41] 22] 37 964 50, FAX : [+[41] 22] 37 961 08 > mailto : radovan.ce...@unige.ch > URL : http://www.unige.ch/sciences/crystal/cerny/rcerny.htm > > > ------------------------------ > > *De :* Matthew Rowles <rowle...@gmail.com> > *Envoyé :* vendredi 30 décembre 2022 13:33 > *À :* Radovan Cerny <radovan.ce...@unige.ch> > *Cc :* Mike Glazer <mike.gla...@physics.ox.ac.uk>; RIETVELD_L > Distribution List <rietveld_l@ill.fr> > *Objet :* Re: "2d materials don't exist" editorial?? > > > > If you want to have a rant, just have a look at the wikipedia page for > single-layer materials. > > > > Phosphorene is particularly egregious: > https://en.wikipedia.org/wiki/File:Phosphorene_structure.png > > > > On Fri, 30 Dec 2022 at 20:30, Radovan Cerny <radovan.ce...@unige.ch> > wrote: > > OK, I understand. Thank you Mike. > > > > The graphene is then 2P material with the layer group p6/mmm. Can somebody > give me an example of a 2D material with the plane group p6mm? > > > > Thank you > > > > Radovan > > > > Radovan Cerny > Laboratoire de Cristallographie > Université de Genève > 24, quai Ernest-Ansermet > CH-1211 Geneva 4, Switzerland > Phone : [+[41] 22] 37 964 50, FAX : [+[41] 22] 37 961 08 > mailto : radovan.ce...@unige.ch > URL : http://www.unige.ch/sciences/crystal/cerny/rcerny.htm > ------------------------------ > > *De :* Mike Glazer <mike.gla...@physics.ox.ac.uk> > *Envoyé :* vendredi 30 décembre 2022 12:20 > *À :* Radovan Cerny <radovan.ce...@unige.ch>; Matthew Rowles < > rowle...@gmail.com> > *Cc :* RIETVELD_L Distribution List <rietveld_l@ill.fr> > *Objet :* Re: "2d materials don't exist" editorial?? > > > > Radovan > > Not quite. Graphene is a 3d material but has periodicity in 2d making its > symmetry given by one of the 80 subperiodic layer groups. > > Mike Glazer > > > > Get Outlook for Android <https://aka.ms/AAb9ysg> > ------------------------------ > > *From:* rietveld_l-requ...@ill.fr <rietveld_l-requ...@ill.fr> on behalf > of Radovan Cerny <radovan.ce...@unige.ch> > *Sent:* Friday, December 30, 2022 11:07:52 AM > *To:* Matthew Rowles <rowle...@gmail.com> > *Cc:* RIETVELD_L Distribution List <rietveld_l@ill.fr> > *Subject:* RE: "2d materials don't exist" editorial?? > > > > Thank you Matt, > > > > for bringing this subject which I have never taken too seriously, butt as > Massimo pointed out in his paper, there are important differences in what > symmetry allows for 2D and what for 2P, for example. > > > > I feel now a bit responsible, because my colleagues at the Quantum matter > dpt. at UNIGE are working on layered pnictides and call them always 2D > materials, which is not correct. They are 2P materials. I will try to > educate them now, even if I am retired. Maybe they can call them 2D > materials if they talk about the physical properties rather than about the > structure? > > I have already tried to introduce then in the OD theory for polytypic > structures, but without too much success. They prefer to do their DFT > modelling rather than have a look on what has been already done. > > > > A test, whether I have properly understood Massimo: Graphen is 2D > material, but when I attach anything to it or take more than one layer of > graphen, it becomes 2P material, right? > > > > Have a nice end of the year > > > > Radovan > > > > Radovan Cerny > Laboratoire de Cristallographie > Université de Genève > 24, quai Ernest-Ansermet > CH-1211 Geneva 4, Switzerland > Phone : [+[41] 22] 37 964 50, FAX : [+[41] 22] 37 961 08 > mailto : radovan.ce...@unige.ch > URL : http://www.unige.ch/sciences/crystal/cerny/rcerny.htm > ------------------------------ > > *De :* rietveld_l-requ...@ill.fr <rietveld_l-requ...@ill.fr> de la part > de Matthew Rowles <rowle...@gmail.com> > *Envoyé :* lundi 26 décembre 2022 11:08 > *À :* Alan W Hewat <alan.he...@neutronoptics.com> > *Cc :* Leopoldo Suescun <leopo...@fq.edu.uy>; RIETVELD_L Distribution > List <rietveld_l@ill.fr> > *Objet :* Re: "2d materials don't exist" editorial?? > > > > 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 > > > > > > > > > > > > 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/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > >
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