RE: "2d materials don't exist" editorial??

[Mike Glazer]

Yes I think that is correct. You can choose either, depending on the level of 
approximation you think is worth using. However, there is a nagging worry to 
which I do not have a certain answer. It is this.
With normal 3-d crystals we are used to using group theoretical representations 
that are based on a 3-dimensional  Euclidean space, for example when using 
theory to derive properties such as electronic band structures or phonon 
dispersion or the dynamics associated with phase transitions. What happens then 
if we decide to work using plane group symmetry in one case or layer group 
symmetry in the other? Can you be sure that you get the same answer?
I suspect it makes little difference to the actual outcome, but I cannot prove 
that.


Mike Glazer


From: Robert Gould 
Sent: 30 December 2022 14:31
To: Mike Glazer 
Cc: Radovan Cerny ; Matthew Rowles 
; RIETVELD_L Distribution List 
Subject: Re: "2d materials don't exist" editorial??

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 
mailto: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 mailto:radovan.ce...@unige.ch>>
Sent: 30 December 2022 12:44
To: Matthew Rowles mailto:rowle...@gmail.com>>
Cc: Mike Glazer 
mailto:mike.gla...@physics.ox.ac.uk>>; RIETVELD_L 
Distribution List mailto: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
[http://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Graphen.jpg/220px-Graphen.jpg1z@]
Single-layer materials - 
Wikipedia
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 mailto:rowle...@gmail.com>>
Envoyé : vendredi 30 décembre 2022 13:33
À : Radovan Cerny mailto:radovan.ce...@unige.ch>>
Cc : Mike Glazer 
mailto:mike.gla...@physics.ox.ac.uk>>; RIETVELD_L 
Distribution List mailto: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 
mailto: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

Re: "2d materials don't exist" editorial??

[Robert Gould]

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 
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 
> *Sent:* 30 December 2022 12:44
> *To:* Matthew Rowles 
> *Cc:* Mike Glazer ; RIETVELD_L Distribution
> List 
> *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
>
>
> 
>
> Single-layer materials - Wikipedia
> 
>
> 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 
> *Envoyé :* vendredi 30 décembre 2022 13:33
> *À :* Radovan Cerny 
> *Cc :* Mike Glazer ; RIETVELD_L
> Distribution List 
> *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 
> 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 
> *Envoyé :* vendredi 30 décembre 2022 12:20
> *À :* Radovan Cerny ; Matthew Rowles <
> rowle...@gmail.com>
> *Cc :* RIETVELD_L Distribution List 
> *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 
> --
>
> *From:* rietveld_l-requ...@ill.fr  on behalf
> of Radovan Cerny 
> *Sent:* Friday, December 30, 2022 11:07:52 AM
> *To:* Matthew Rowles 
> *Cc:* RIETVELD_L Distribution List 
> *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
> 

RE: "2d materials don't exist" editorial??

[Mike Glazer]

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 
Sent: 30 December 2022 12:44
To: Matthew Rowles 
Cc: Mike Glazer ; RIETVELD_L Distribution List 

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
[http://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Graphen.jpg/220px-Graphen.jpg1z@]
Single-layer materials - 
Wikipedia
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 mailto:rowle...@gmail.com>>
Envoyé : vendredi 30 décembre 2022 13:33
À : Radovan Cerny mailto:radovan.ce...@unige.ch>>
Cc : Mike Glazer 
mailto:mike.gla...@physics.ox.ac.uk>>; RIETVELD_L 
Distribution List mailto: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 
mailto: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 
mailto:mike.gla...@physics.ox.ac.uk>>
Envoyé : vendredi 30 décembre 2022 12:20
À : Radovan Cerny mailto:radovan.ce...@unige.ch>>; 
Matthew Rowles mailto:rowle...@gmail.com>>
Cc : RIETVELD_L Distribution List mailto: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

From: rietveld_l-requ...@ill.fr 
mailto:rietveld_l-requ...@ill.fr>> on behalf of 
Radovan Cerny mailto:radovan.ce...@unige.ch>>
Sent: Friday, December 30, 2022 11:07:52 AM
To: Matthew Rowles mailto:rowle...@gmail.com>>
Cc: RIETVELD_L Distribution List mailto: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 

RE: "2d materials don't exist" editorial??

[Radovan Cerny]

Uff, I do not know who has written this page

https://en.wikipedia.org/wiki/Single-layer_materials#C:_graphene_and_graphyne
[http://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Graphen.jpg/220px-Graphen.jpg1z@]

Single-layer materials - 
Wikipedia
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 
Envoyé : vendredi 30 décembre 2022 13:33
À : Radovan Cerny 
Cc : Mike Glazer ; RIETVELD_L Distribution List 

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 
mailto: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 
mailto:mike.gla...@physics.ox.ac.uk>>
Envoyé : vendredi 30 décembre 2022 12:20
À : Radovan Cerny mailto:radovan.ce...@unige.ch>>; 
Matthew Rowles mailto:rowle...@gmail.com>>
Cc : RIETVELD_L Distribution List mailto: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

From: rietveld_l-requ...@ill.fr 
mailto:rietveld_l-requ...@ill.fr>> on behalf of 
Radovan Cerny mailto:radovan.ce...@unige.ch>>
Sent: Friday, December 30, 2022 11:07:52 AM
To: Matthew Rowles mailto:rowle...@gmail.com>>
Cc: RIETVELD_L Distribution List mailto: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 
mailto:rietveld_l-requ...@ill.fr>> de la part de 
Matthew Rowles mailto:rowle...@gmail.com>>
Envoyé : lundi 26 décembre 2022 11:08
À : Alan W Hewat 
mailto:alan.he...@neutronoptics.com>>
Cc : Leopoldo Suescun mailto:leopo...@fq.edu.uy>>; 
RIETVELD_L Distribution List mailto:rietveld_l@ill.fr>>
Objet : Re: "2d materials don't exist" 

Re: "2d materials don't exist" editorial??

[Matthew Rowles]

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  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 
> *Envoyé :* vendredi 30 décembre 2022 12:20
> *À :* Radovan Cerny ; Matthew Rowles <
> rowle...@gmail.com>
> *Cc :* RIETVELD_L Distribution List 
> *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 
> --
> *From:* rietveld_l-requ...@ill.fr  on behalf
> of Radovan Cerny 
> *Sent:* Friday, December 30, 2022 11:07:52 AM
> *To:* Matthew Rowles 
> *Cc:* RIETVELD_L Distribution List 
> *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  de la part
> de Matthew Rowles 
> *Envoyé :* lundi 26 décembre 2022 11:08
> *À :* Alan W Hewat 
> *Cc :* Leopoldo Suescun ; RIETVELD_L Distribution
> List 
> *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, 
> 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,  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,  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 

RE: "2d materials don't exist" editorial??

[Radovan Cerny]

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 
Envoyé : vendredi 30 décembre 2022 12:20
À : Radovan Cerny ; Matthew Rowles 
Cc : RIETVELD_L Distribution List 
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

From: rietveld_l-requ...@ill.fr  on behalf of 
Radovan Cerny 
Sent: Friday, December 30, 2022 11:07:52 AM
To: Matthew Rowles 
Cc: RIETVELD_L Distribution List 
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  de la part de 
Matthew Rowles 
Envoyé : lundi 26 décembre 2022 11:08
À : Alan W Hewat 
Cc : Leopoldo Suescun ; RIETVELD_L Distribution List 

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, 
mailto: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, 
mailto: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, 
mailto: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 

Re: "2d materials don't exist" editorial??

[Mike Glazer]

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

From: rietveld_l-requ...@ill.fr  on behalf of 
Radovan Cerny 
Sent: Friday, December 30, 2022 11:07:52 AM
To: Matthew Rowles 
Cc: RIETVELD_L Distribution List 
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  de la part de 
Matthew Rowles 
Envoyé : lundi 26 décembre 2022 11:08
À : Alan W Hewat 
Cc : Leopoldo Suescun ; RIETVELD_L Distribution List 

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, 
mailto: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, 
mailto: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, 
mailto: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 
mailto: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, 
mailto: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.png]




On Fri, 23 Dec 2022 at 09:53, Matthew Rowles 
mailto: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 

RE: "2d materials don't exist" editorial??

[Radovan Cerny]

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  de la part de 
Matthew Rowles 
Envoyé : lundi 26 décembre 2022 11:08
À : Alan W Hewat 
Cc : Leopoldo Suescun ; RIETVELD_L Distribution List 

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, 
mailto: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, 
mailto: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, 
mailto: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 
mailto: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, 
mailto: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.png]




On Fri, 23 Dec 2022 at 09:53, Matthew Rowles 
mailto: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
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