[DFTB-Plus-User] CNT Gate Settings

[George D Kubas]

Thank you for all your help. I will use it to better improve my calculations and I will let you know how it goes.


Cheers,

George


George D. Kubas
Materials Science PhD. Candidate
Youngstown State University
gdkubas at student.ysu.edu
(330) 261-2967


________________________________
From: dftb-plus-user-bounces at mailman.zfn.uni-bremen.de <dftb-plus-user-bounces at mailman.zfn.uni-bremen.de> on behalf of Gabriele Penazzi <penazzi at uni-bremen.de>
Sent: Wednesday, December 16, 2015 4:16 AM
To: dftb-plus-user at mailman.zfn.uni-bremen.de
Subject: Re: [DFTB-Plus-User] CNT Gate Settings

I understand you expect it semiconductor, but I don't understand why it should be n-type, isn't it intrinsic.

Anyway yes, there is a way to force doping in a virtual crystal approximation by increasing or decreasing the reference neutral occupation. This can be achieved in the new MPI version with the keyword CustomReferenceOcc or in the old serial version by hacking the SK files. The doping in the reference I sent you was realized in this way.

Note that in a non metallic system DFTB+ defines the Fermi level numerically somewhere in the gap, usually near a band edge, due to the way it is numerically defined. If I work with a semiconductor at room temperature I use to shift the Fermi level in the middle of the gap by hand.

The Fermi is 0 in the detailed.out after a device calculation because in an open boundary set up the total charge is not fixed, and a Fermi level for the whole system is not well defined out of equilibrium.

Best,
Gabriele

On 12/14/2015 09:47 PM, George D Kubas wrote:

An 8,0 CNT in vacuum should be inherently n-type due to chirality , but maybe I need to virtually dope the system to impose this in the program? If so, please excuse my ignorance in this regards. The fermi energy for the SWCNT contacts is 3.84 roughly when calculated, but when the device file is run the fermi energy reads 0 in the detailed.out. This may be the reason for some of my errors. I am going to try the MPI version as well which I was just able to install.


George D. Kubas
Materials Science PhD. Candidate
Youngstown State University
gdkubas at student.ysu.edu<mailto:gdkubas at student.ysu.edu>
(330) 261-2967


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--
Dr. Gabriele Penazzi
BCCMS - University of Bremen

http://www.bccms.uni-bremen.de/
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phone: +49 (0) 421 218 9328
fax: +49 (0) 421 218 4764
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