Mailman 3 November 2015 - Kwant-discuss

Direction-dependent hopping
by Oscar Erlandsson Nov. 18, 2015

Nov. 18, 2015

Hello all, In Section 2.3 of the Kwant 1.0.3 documentation it says: "(...) it is enough to specify one direction of the hopping (i.e. when specifying (1, 0) it is not necessary to specify (-1, 0)), Builder assures hermiticity." However, if I want the hopping in the e.g. -x direction to be different from that in the +x direction, how do I implement this? Is it OK to write: sys[kwant.builder.HoppingKind((0, 0, -1), lat, lat)] = value1 sys[kwant.builder.HoppingKind((0, 0, 1), lat, lat)] = value2 Will the above code produce the desired result? Thanks, Oscar Erlandsson

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(no subject)
by edilon francisco Nov. 11, 2015

Nov. 11, 2015

What is the default method used to compute smatrix? I'm not sure whether it is the same 'wave-matching analysis' or Usiki's method.

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several repeated regions in the scattering region
by Sergey Nov. 11, 2015

Nov. 11, 2015

Dear Colleagues, Is there an efficient way to study the problem of 2-terminal conductance via a scattering region that is formed out of N repeated configurations connected in a sequence? I assume that RGF type of algorithm is to be used and I need to compute the N-th power of Green's function between the "connecting ends" of repeated configuration. So, I need the Greens function object of Kwant, reduce it to connecting bits of boundary and then take the N-th power. Is there any better way via the scattering formalism? Thank you and best wishes, Sergey

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Plot setting
by Weiyuan Tong Nov. 9, 2015

Nov. 9, 2015

Dear all, I have a question about the figure plotting of kwant, or maybe it is just a python question. When we plot more than one figures in kwant, we need to close the first figure to let the second one start to be plotted. Can we plot all the figures without manually closing the figure window? Maybe a silly question, i am really not good at python. Weiyuan Tong

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kkghosh
by kamal ghosh Nov. 9, 2015

Nov. 9, 2015

Dear all members, I am trying with a nanodot 10 nm. and lead width 7 nm. to find conductance of the dot under no crystal defect and also under some missing atoms creating a defect. The system and conductance without defect is no problem; but I cannot introduce the defect properly in the code and so I cannot get the conductance. However, in case of quantum wire I have succeeded to build both the defective and not defective structure and got the conductance. In fact, when the lattice structure is on hexagonal and bipartite then the problem comes; it is no in case of square lattice. I think I fail to to point out the location of the atoms in case of spherical dot. Cheers to all. K.K.Ghosh

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QZ Iteration fails
by Maximilian Trescher Nov. 9, 2015

Nov. 9, 2015

Dear kwant users and developers, this is my first post to this list, I'm a PhD student from Berlin. Currently I'm trying to implement a lattice model of a pyrochlore slab in kwant. I found a (more or less straightforward) way to introduce periodic boundary conditions in the system in the maillinglist archive. This works very nicely as long as I keep the periodicity along a lattice vector. But I run into problems when I choose different directions: Most of the time all solvers fail with a "LinAlgError: QZ iteration failed to converge in zgges". I know about this post http://comments.gmane.org/gmane.comp.science.kwant.user/372 but in my case it occurs not only for a band bottom, but for a range of energies. To give you all the details I prepared a Ipython notebook that you can view here: http://nbviewer.ipython.org/gist/faucon/729050da5e3f2eae1bb8# (Note that the inclusion of complex next-nearest-neighbor hopping is crucial to produce the error, I tried to create the shortest example which reproduces my problem). Do you have any idea how to circumvent this problem? Is it somehow related to http://netlib.org/lapack/Errata/vrac/lapack_known_issues.html#QZ this problem in Lapack? I would be thankful for any hint, Best, Maximilian

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Geometrical Unit
by Dedi Setiabudidaya Nov. 5, 2015

Nov. 5, 2015

Dear Sir/ Madam, I use the codes below to build my graphene system.Could you tell me what is the unit of L and W (or x and y) ?...L = 8.0W = 6.0def rectangle(pos): x, y = pos return -L < x < L and -W < y < Wdef lead_shape(pos): x, y = pos return -W/4.0 < y < W/4.0...Thank you in advance. Best Regards, Dedi

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