QuantumATK Forum
QuantumATK => General Questions and Answers => Topic started by: medeepak on November 23, 2010, 16:46
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hi
i am new to this forum
can anyone please tell me how to find bandgap/bandstructure of a graphene nanoribbon
i followed the tutorial but bandstructure option is not there in analysis function
also i dont know how to access the eigen values that are computed during the run as band gap can be found from there using homo and lumo values
regards
deepak
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If you follow this tutorial (http://quantumwise.com/documents/tutorials/BasicGrapheneTutorial/XHTML) for ATK 10.8, you will see how to plot the band structure of a GNR. The band gap can often be found easily by inspection in these 1d systems; more generally, the best way is to compute the density of states however.
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hi
i tried building the same structure through builder but in the density of states plot i dont get any value
what can be the reason
also if i use custom builder i dont get density of states in analysis option
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Your question is quite confusing :) Please provide (much) more details, like scripts, plots, etc.
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hi
i have attached the structure i made
when i simulate DOS the plot is empty
kindly find the problem with my structure
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If you do the band structure calculation, the band gap can be easily found from the band structure plot. Sometime, due to the broadening technique used in the DOS calculation, the band gap found from the DOS plot may look smaller than the one obtained from the band structure plot.
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hi
bandstructure option is not there in analysis menu when i build it this way
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I took your file and dropped it on the Scripter in VNL 10.8. If I double-click "Analysis", I can choose "Bandstructure" (although of course first you should have a "New Calculator" there too). Set the relevant parameters as needed, including the NetCDF file, run the calculation, then locate the produced NC file, and select the band structure and click the "Plot" button.
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Hi
i have the new calculator menu while i dont have band structure under analysis
i am using vnl in trial license
is it because of that??
and can you kindly tell me why am i not getting any values in my density of states plot
regards
deepak
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No, it's not because of the trial license. I have no idea why you don't see it. Double-click "Analysis" and you see what? A menu will open up, containing a lot of quantities, incl BandStructure.
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Options under my analysis menu in order are
density of states
effective potential
eigenstate
electron density
electron difference density
electrostatic difference potential
external potential
forces
molecular energy spectrum
mulliken population
total energy
Band Structure is not there
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This means your system is a molecule, not a periodic structure. Band structure can only be computed for BulkConfigurations.
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so is there any way to find its band gap???
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i noticed this error now only
There are no atoms in my left electrode
even if i increase its width it dooesnt go away
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hi
i wrote a script file for my molecular configuration to find energy bands which requires ATK.KohnSham Method
but when i try to run it through
$ atk <filename>.py
i get the error
atk command not found
i tried vnl <filename>.py
now the software opens but still i dont think it is importing ATK.KohnSham method
it shows the error
ATK.KohnSham module not found
i tried to add the path variable using
export PATH=$PATH:/opt/QuantumWise/atk-10.8.2/vnl/bin
still the same error persists
kindly help
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The ATK.KohnSham module is only relevant for version 2008.10.
In 10.8 you run "atkpython", not "atk".
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Well... it's different in 10.8. The contents of the module are available, but you don't need to import it. But the syntax is a little bit different, you can't just reuse the script from 2008.10.
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Hi
thanks for the reply
i computed density of states for the file i attached in one of my previous posts
all DOS values are zero
can you kindly tell me what might have been the problem
i am stuck at it for a long time now
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Please post the full complete script that you ran, as well as the log file.
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Hi
i have attache d my log and script file in this zip file
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The script attached is a molecule. You should compute the density of states for a periodic structure. Even if it technically is possible to do it for a molecule, I don't think the results will be what you are looking for.
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i calculated its molecular energy spectrum as well
but even in that i get straight lines parallel to x axis
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Of course, it's a molecule. All molecules have discrete spectra (sharp levels).
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Thanks for your replies
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Hi
i created a small distortion in graphene nanoribbon as given in the tutorial
http://www.quantumwise.com/documents/tutorials/BasicGrapheneTutorial/index.html/chap.zigzag_transport.html#id1286600
i want to find its band gap
since its a molecule i cannot run bandstructure calculations and as i understand from discussion even DOS will not give correct results
so how to do it?
kindly help
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If you follow the tutorial, it's a periodic structure, not a molecule. At some point you, by mistake, must be converting the structure to a molecule. Don't :)
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Hi
i corrected my mistake and plotted the bandstructure and density of states plot for the structure
the bandstrcuture consists of straight lines and in density of states there is a small peak near zero instead of discontinuity between HOMO and LUMO
what might have been the problem
i have attached my script file and log file with it
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The bands around the Fermi level are not flat. Results look ok.