[Wannier] Tight binding band structures based on ab-initio-derived hopping parameters

[Giovanni Pizzi]

Dear Janos,
what you ask is very interesting, but if I understand correctly what you 
need, at the moment there is no such tool in Wannier90.

This is not too easy to be done in a general way (even if, in principle, 
I think it can be done): you must have a reliable way to "join" together 
the Hamiltonian matrices (in real space) of different regions of the system.
These different regions should probably be overlapping, and one will 
have to consider the Wannier functions centered on atoms that are in the 
"inner" part of each region (Wannier functions at the edges of each 
region will be in general different from the actual Wannier functions of 
the global system, because they will "feel" the fact that they are at 
the edge). How big the overlapping part has to be should be determined 
in some way from the cutoff that you want to use.

If you instead want to obtain a sort of TB parametrization which is 
general and transferable, I think that this task is even more difficult.

Cheers,
Giovanni Pizzi



-------- Original Message --------
Subject: [Wannier] Tight binding band structures based on 
ab-initio-derived hopping parameters
Date: Sun, 15 Apr 2012 17:31:14 +0000
From: Kiss, Ioan <kissi at uni-mainz.de>
To: wannier at quantum-espresso.org <wannier at quantum-espresso.org>

Dear Wannier90 users and developers,

I am a novice user of the wannier package (just started working trough 
the examples),
and I have a question which sound probably trivial and naive to most of 
you.
Namely, I have seen that one can print the seedname_hr.dat file,
but I could not figure out whether there is already a code available
in the Wannier90 or in the Quantum-Espresso package which can directly
use this file to create ab-initio-derived tight binding models for
band structure calculations.
What I mean by this is that by using the Wannier90 package or the
Quntum-Espresso package how can one use these hopping parameters
computed for small systems based on ab-initio calculations to evaluate
the band structure of similar but large arbitrary extended systems
just like the philosophy of the work published by
Lee et al. PRL 95, 076804 (2005) and
Cantele et al. Nano Letters Vol. 9, No. 10 3425 (2009).
So far the only thing what I could find (at least in the Quantum-Espresso
repository) are the wannier_ham.f90 and related routines, but as far as
I see this is meant to be used together with DMFT. Does this mean that
one has to program for himself the tight-binding part for each particular
system of interest, or there are already such codes readily available?
In case if Wannier90 is able to do this, than I have really overlooked
this feature, but in that case could you please give a short description
of what are the steps between to perform such tasks with Wannier90.

I would like to thank you in advance for any helpful comment.

Best regards,
Janos Kiss.

==========================================
   Dr. Janos Kiss      e-mail: kissi at uni-mainz.de
   Johannes Gutenberg-Universitaet
   Institut f. Anorg. u. Analyt. Chemie
   AK Prof. Dr. Claudia Felser
   Staudinger Weg 9 / Raum 01-230
   55128 Mainz/ Germany
   Phone: +49-(0)6131-39-22703
   Fax:     +49-(0)6131-39-26267
   Web: http://www.superconductivity.de/
  =========================================
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-- 
Giovanni Pizzi
Post-doctoral Research Scientist
EPFL STI IMX THEOS
MXC 319 (Bâtiment MXC)
Station 12
CH-1015 Lausanne (Switzerland)
Phone: +41 21 69 31159