Den fre. 4. sep. 2020 kl. 22.00 skrev zhyphy <zh...@mails.jlu.edu.cn>:
> Dear All，
> I have some questions in the process of learning Green's function.I hope
> someone can help me.
> (1) The surface Green function contains all the informations about
> interaction between electrodes and scatter region, but for Transiesta, we
> must add some buffer layers, so the surface GF in transiesta will be
> the interaction between electrodes and buffers? if so, how can I get the
> real information about the coupling between the electrode and the central
> region?
>
Not exactly, the surface green function contains the self-energy of a truly
bulk electrode. Thus it contains the information about how it interacts
with another bulk part.
The spectral density of states arising from incoming states from a given
electrode will be a measure of the coupling between the electrode and the
central region.
> (2) The current obtained by Landauer formula is related to transimisson,
> so all the current is resonant transport current, it that right? Then, how
> to calculate the tunneling current?
>
The transiesta NEGF is ballistic transport.
To calculate the tunneling current you'll have to just add some vacuum,
however, be careful about the vacuum region due to Siesta's range limited
basis set. You'll have to add ghost-orbitals or extended orbitals, if you
want to use TranSiesta for this.
> (3) The GF formula have a small complex number (called eta ), why is this
> number introduced? For Transiesta code, how to deal with this formula?
> Is it represented by 0.0000001j ?
>
Because you can't invert a singular matrix. The Green function is
G(E) \propto \frac{1}{E - \eig}
If E == \eig it blows up to infinity. To remove this infinity we add a
small imaginary number i\eta which ensures finiteness. This then acts as a
broadening value. Please derive what the density of states looks for the
Green function (hint Lorentzian).
> Thanks,
> zhy
>
>
>
> --
> SIESTA is supported by the Spanish Research Agency (AEI) and by the
> European H2020 MaX Centre of Excellence (http://www.max-centre.eu/)
>
--
Kind regards Nick
--
SIESTA is supported by the Spanish Research Agency (AEI) and by the European
H2020 MaX Centre of Excellence (http://www.max-centre.eu/)
