[Pw_forum] SCF input file for 2D graphene sheet

[Pascal BOULET]

Hello Cam,
you should not set celldm(3) to 0. QE works with 3D periodic models. So if you are interested in graphene sheet, you have to find the c length so that the graphene sheet does not interact with its images in the c direction. c=10-15 angs should do the job but you have to check this.
BTW, if you intend to relax the structure, the c parameter should be fixed. Use the cell_dofree keyword for this, as you mentioned.
Best regardsPascal

Cameron Foss <cjfoss at umass.edu> wrote:Hello all,
I have looked through a lot of the forum and have yet to find anything that helps with this question. However, if I am wrong where should I look for the answer to this?
I am trying to run a scf simulation of a 2D graphene sheet of carbon atoms. Graphite is an hexagonal structure and uses ibrav=4, I have tried using this and setting celldm(3)=0, to indicate no height component, but that doesn't work. I have also tried indicating a free lattice (ibrav=0) and setting c=0, and setting the CELL_PARAMETERS card vectors to only having 2D components (ie the z-components are set to 0). However, that too has errors when I try running the pw.x code or loading the file in XCrySDen. 
(NOTE: I have been playing with QE-5.1 for only the past few weeks and am using XCrySDen to visualize the generated unit cells.) 
Particularly the error I get from XCrySDen in the terminal is: Num of Atoms =0, Num of Frames =0.
I have also looked at the cell_dofree variable in the CELL card. but setting that to xy does not seem to work either, which I would suspect since I still have to define  a height to the structure. Are any of these approaches a viable way of getting just a 2D structure of graphene and I might be missing something? Or should i be going about this in another way? 
Best,Cam
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>-----------------
Pascal Boulet
Aix-Marseille University 
MADIREL Laboratory
Avenue Normandie-Niemen
13397 Marseille Cedex 20
Email: pascal.boulet at univ-amu.fr
Tel. +33 413 55 18 10
Fax  +33 413 55 18 50
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