Dear Siddheshwar,

The short answer to your question is that the (many-body) ground state of the
system corresponds to filling up all the (scattering) states of the system up to
the Fermi energy. When one wants to get the I-V curve, one fills up the
states differently depending on the lead to which they "belong"
(belong is probably a misleading word as those are eigenstates of the whole infinite system).

The long answer is too long, you should dive into the theoretical framework which is
quite independent of Kwant. A possible entry point is the book by Datta
("Mesoscopic physics" or something similar.)

Best regards,

Xavier

Le 4 sept. 2015 à 05:38, siddheshwar chopra <sidhusai@gmail.com> a écrit :

Dear All,
I am a new user who wishes to work with I-V calculations. Please pardon me for asking a very basic question. I have till now worked with the ground state and excited state properties, for which we OPTIMIZE these states.. But I have since long wanted to calculate I-V curves  for nanomaterials, nanocomposites...
I really do not understand exactly what is being done to get this I-V graph. I understand the PROCESS for the same, as seen in the paper (defining the leads, scattering region). But Do we need to optimize the ground state geometries of both the leads and scattering region before adding it in Kwant? Then it seems confusing to me... Because when we wish to study I-V, we apply perturbation to the system, which for me means the "scattering region" is no more in the ground state.. Please explain this to me. Before I understand this properly, I will not be able to start working on it.

OR, please elaborate the need of external code with Kwant. What do we want to achieve by caaling the external code.

Regards,

--
Dr. Siddheshwar chopra,
M.Sc., Ph.D (Physics)
Assistant Professor (Physics),
Amity University, Noida, India.