[DFTB-Plus-User] Compute electrostatic potential with NEGF

Gabriele Penazzi penazzi at uni-bremen.de
Sun Oct 30 14:19:08 CET 2016


Hi Andrea,

I am not sure what you want to do, but dftb as a method may not include 
the details you need.

I see now the point about mulliken charges from your previous mail, but 
the use of mulliken charges is pretty much a direct consequence of the 
way dftb (at least in its current and most popular version) is 
formulated. Nuclei+electron density does not make too much sense, as you 
work in a monopole approximation based on differences with respect to a 
reference configuration. The s-like projection of the potential reflects 
this and is consistent with the usual scc-dftb based on gamma-functional.

For example, you have no potential in a system without self-consistent 
fluctuation. And even if you compare two system with different 
hybridization, if the scc component is zero the real space potential 
will be the same, i.e. zero. So my guess is no, you can not really have 
detailed information about he charge density between atoms and you 
probably have to go at DFT level.

Best,

Gabriele


On 10/29/2016 11:55 PM, Andrea Pedrielli wrote:
>
> Thank you Gabriele,
> If I could, I would ask you another thing. I read in the online 
> tutorial on silicon nanowire that the charge density is expanded in s 
> spherical orbitals weighted with Mullen charges. Part of my interest 
> in compute charge density and potential is take into account the 
> charge density between the atoms, due to the bonds. If the charge 
> density is expanded in s-like orbitals the charge density between the 
> atoms (for example in a nanotube) is still well described?
>
> Andrea
>
> Il sabato 29 ottobre 2016, Gabriele Penazzi <penazzi at uni-bremen.de 
> <mailto:penazzi at uni-bremen.de>> ha scritto:
>
>     Hi Andrea,
>
>     yes, you can do a non transport calculation with the real space
>     Poisson solver, I did the same for the same reason. Whether you
>     can simulate your system or not, however, may depend on the
>     boundary conditions you want to impose. For example, all periodic
>     does not work if I remember right, but for a 1D system you should
>     be able to set up a well defined calculation.
>
>     Gabriele
>
>
>     On 10/28/2016 10:51 PM, Andrea Pedrielli wrote:
>>     Hi users,
>>     I need to compute the electrostatic potential produced by the
>>     charge density from a dftb+ calculation. I know that there is no
>>     possibility using dftb+, but I have seen that in the NEGF package
>>     there is a Poisson solver. In particular I have to compute the
>>     inner and the outer potential of a carbon nanotube, so a 1D
>>     object. Can I use a NEGF package for a non-transport calculation
>>     with the aim of extract the electrostatic potential? I underline
>>     that I need the potential due to the total charge density+nuclei
>>     and Mulliken charges are not suitable for my purpose.
>>
>>     Thank you in advance,
>>
>>     Andrea
>>
>>
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>
>     -- 
>     Dr. Gabriele Penazzi
>     BCCMS - University of Bremen
>
>     http://www.bccms.uni-bremen.de/ <http://www.bccms.uni-bremen.de/>
>     http://sites.google.com/site/gabrielepenazzi/
>     <http://sites.google.com/site/gabrielepenazzi/>
>
>     phone: +49 (0) 421 218 9328
>     fax: +49 (0) 421 218 4764
>
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-- 
Dr. Gabriele Penazzi
BCCMS - University of Bremen

http://www.bccms.uni-bremen.de/
http://sites.google.com/site/gabrielepenazzi/

phone: +49 (0) 421 218 9328
fax: +49 (0) 421 218 4764
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