Thanks for your prompt reply Mr. Wintal.
I did not calculate the Green function and obtained the G-E diagram using the transmission method introduced in the Green function class.
Another method introduced in this class is conductance_matrix (),
( https://kwant-project.org/doc/1/reference/generated/kwant.solvers.common.GreensFunction.html?highlight=green%20function  )
which relates the current vector to the voltage vector.
Can I use this method and get to the I-V diagram?
I also want to check the temperature parameter in this system and see the device's behavior under different temperatures.
thanks
Leo

On Tue, Jun 30, 2020 at 4:29 PM Xavier Waintal <xavier.waintal@cea.fr> wrote:
dear Leo,

If you have calculated the conductance G(E) of a 2 terminal device,
the current I at finite voltage V is given by

I = Integral dE  G(E) [ f(E-mu_L) - f(E-mu_R) ]
where mu_L and mu_R are the chemical potential of the two electrodes, f(E) is
the Fermi function. mu_L - mu_R = eV where V is the voltage drop across the devices.

Beware that this equation assumes a NON INTERACTING system and can lead to physically wrong results.
(It neglects the electrostatic which becomes almost always relevant at finite bias).

Best regards,
Xavier


> Le 30 juin 2020 à 13:37, <loojoo026@gmail.com> <loojoo026@gmail.com> a écrit :
>
> dear all
> I have done my project using Kwant and I have drawn a conductance-energy diagram for the system.
> The question I have is how can I get the current-voltage diagram?
> thanks
> Leo