Messages

1066

General Questions and Answers / Re: Why does carrier density in GFET and GFET(reduced the gate) is the same?

« on: April 21, 2017, 21:30 »

I do not say that charge density is not important for your study, but my suggestion is to first check if there is any effect of gating on the transmission spectrum, as it is likely to be more sensitive to the applied gate voltage than the charge density. If there is no effect on the transmission, it would then mean that there is something wrong with the calculation setup. The charge density might not be a good quantity for this check because the gate-induced changes in the density can be rather small to be visible on the graph you have posted.

1067

General Questions and Answers / Re: Why does carrier density in GFET and GFET(reduced the gate) is the same?

« on: April 21, 2017, 11:59 »

Why would you expect a significant change in the electron density? It is more important to verify if there is any effect of gating on the transmission spectrum.

I would also try increasing the metal gate thickness from 0.5 Angs to something like 5 Angs. I am not sure that the dielectric spacer thickness of 3 Angs is realistic as well.

1068

General Questions and Answers / Re: Band decomposed charge density

« on: April 20, 2017, 13:24 »

Yes, 'quantum_number' can be seen as a band index. Assuming that you have also calculated the band structure, you may then get the energies from the band structure, see the Bandstructure class description and useful notes in the reference manual at http://docs.quantumwise.com/manuals/Types/Bandstructure/Bandstructure.html.

1069

General Questions and Answers / Re: Band structure

« on: April 20, 2017, 12:22 »

If the CNT is infinite along the nanotube axis, you can do it in a regular way as described in the following tutorial http://docs.quantumwise.com/tutorials/crystal_bandstructure/crystal_bandstructure.html. Note that you have to set the k-route in the Band structure analysis, e.g., along the G->Z direction, provided that the CNT axis is in the z direction. 

1070

General Questions and Answers / Re: Band decomposed charge density

« on: April 19, 2017, 20:46 »

I guess you need to do integration of the DOS multiplied by the Fermi-Dirac distribution with respect to the energy from the bottom of the conduction band to infinity. But if your silicon is an intrinsic semiconductor, i.e., the Fermi level is in the middle of the band gap, the conduction band electron density will then be zero at 0 K, or rather small even at room temperature. I assume you are considering an n-type doped silicon.

1071

General Questions and Answers / Re: Energy Bands vs Distance

« on: April 19, 2017, 20:33 »

For atom manipulation, you may try using the Move tool in the Builder, see http://docs.quantumwise.com/tutorials/builder_manual/builder_movetool/builder_movetool.html#section-move-tool.

1072

General Questions and Answers / Re: Band decomposed charge density

« on: April 19, 2017, 12:01 »

Please have a look at this forum post https://quantumwise.com/forum/index.php?topic=4962.msg21464#msg21464 on a similar topic.

1073

General Questions and Answers / Re: Energy Bands vs Distance

« on: April 18, 2017, 11:46 »

I am not sure about what you mean by "provide stress value myself at the interface". You may use the Interface Builder plugin in the Builder tools. In this case, you choose the lateral supercell for the interface structure, based on the mean interface strain value and the supercell size.

Usually, one wants to use a supercell with virtually no interface strain, but this might need to be compromised against the supercell size, which determines the computational cost of your interface calculations. So, you should adopt a supercell structure with a rather small interface strain, having in mind that you must be able to do the further calculations within a decent computational time. Also, the interface strain should not be too large to alter the physical characteristics of the interface that are relevant for your study.

1074

General Questions and Answers / Re: Energy Bands vs Distance

« on: April 15, 2017, 15:30 »

To calculate the PLDOS across an interface, one should build it as a one- or two-probe device, as done in the tutorial, http://docs.quantumwise.com/casestudies/ag_si_interface/ag_si_interface.html. In this case, the PLDOS analysis object will be available in the Scripter.

1075

General Questions and Answers / Re: Energy Bands vs Distance

« on: April 13, 2017, 21:05 »

PLDOS is an analysis object that can be added to the script in the VNL Scripter as any other analysis object, see also the tutorial if you want to do the analysis in a post-processing manner from a file.

1076

General Questions and Answers / Re: Question about modeling diffusion

« on: April 12, 2017, 17:42 »

You may have a look at the following tutorial http://docs.quantumwise.com/tutorials/combining_potentials/combining_potentials.html. I would like to notice that developing a reliable classical potential parameter set can be a study on its own that may take really a lot of time. So, it might be an idea to first look for a parameter set for your system of interest in the literature. 

1077

General Questions and Answers / Re: Virtual NanoLab Error

« on: April 12, 2017, 15:36 »

Regarding #2 How many projects do you have? This step takes no time for me.

Regarding the error message, I cannot reproduce it in ATK-2016.4 in Windows 10. Could you check if you have the latest GrapheneBuilder plugin installed? For that, you should select Help in the VNL menu, then click on AddOn Manager, and finally do search for GrapheneBuilders plugin and update it, if needed.   

1078

General Questions and Answers / Re: VNL Crash: OpenGL Error

« on: April 12, 2017, 14:16 »

Could you post a snapshot of the "About VNL & ATK" information on your mac? Just go to 'Help' in the VNL menu, and click on 'About VirtualNano Lab' to get the information required. 

It would also be of great help if you could provide an output of the command "glxinfo". Please enclose a text file with the output to your post.

1079

General Questions and Answers / Re: Virtual NanoLab Error

« on: April 12, 2017, 14:01 »

Please could you describe step-by-step what you did to get this error? 

1080

General Questions and Answers / Re: how do we calculate spin transport in finite bias?

« on: April 10, 2017, 23:00 »

Regarding #2, the answer is "no" as you say.

Regarding #3, you may first do left and right electrodes in a separate calculation and save the left and right electrode configurations into the corresponding nc-files:

....
left_electrode.setCalculator(left_electrode_calculator)
left_electrode.update()
nlsave('left_electrode.nc', left_electrode)
right_electrode.setCalculator(right_electrode_calculator)
right_electrode.update()
nlsave('right_electrode.nc', right_electrode)


And you may then just read the electrode configurations from the nc-files (instead of actually doing electrode calculations) while  doing the device calculations for different bias voltages:

left_electrode = nlread("left_electrode.nc")[0]
right_electrode = nlread("right_electrode.nc")[0]
.....