Mailman 3 January 2022 - Kwant-discuss

How to attach a lead to particular position of honeycomb lattice
by sahu.ajit92＠gmail.com Feb. 4, 2022

Feb. 4, 2022

Dear Sir, I am new to kwant. How to attach a lead to a particular portion(upper side of the square) of the honeycomb structure. sym1 = kwant.TranslationalSymmetry(lat.vec((0,1))) lead1 = kwant.Builder(sym1) def lead2_shape(pos): x, y = pos return 0<x<10 lead1[lat.shape(lead2_shape, (2,0))]=3 lead1[lat.neighbors()] = -1 I used the above code to attach the second lead but it didn’t attach to the correct place. I want to attach the lead to the upper side of the square. main code Wnr=10 lnr=10 a=1 lat=kwant.lattice.honeycomb(a) def rect(pos): x,y=pos return 0<x<lnr and 0<y<Wnr model1 = kwant.Builder() model1[lat.shape(rect,(1,1))] = 3 model1[lat.neighbors()] =-1 ##########lead shape function def lead1_shape(pos): x, y = pos return 0 < y < 10 def lead2_shape(pos): x, y = pos return 0<x<10 ##########1st lead########## sym = kwant.TranslationalSymmetry(lat.vec((-1,0))) #from the left sym.add_site_family(lat.sublattices[0], other_vectors=[(-1, 2)]) sym.add_site_family(lat.sublattices[1], other_vectors=[(-1, 2)]) lead = kwant.Builder(sym) lead[lat.shape(lead1_shape, (1,1))]=3 lead[lat.neighbors()] = -1 model1.attach_lead(lead) ##########problem in 2nd lead, from this below code it attach to other position########## sym1 = kwant.TranslationalSymmetry(lat.vec((0,1))) lead1 = kwant.Builder(sym1) lead1[lat.shape(lead2_shape, (2,0))]=3 lead1[lat.neighbors()] = -1 model1.attach_lead(lead1) kwant.plot(model1) Anyone, please help please see this image in below link, I want to attach the second lead in the red-circled position of the figure https://drive.google.com/file/d/15ORyo4j_tAvgC8jaT5lQxmQNS6e0QoOF/view?usp=…

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Elements of a scattering matrix
by Lorenzo BAGNASACCO Feb. 4, 2022

Feb. 4, 2022

Dear Kwant community, I am a physics student and I am approaching to Kwant to solve simple problems of scattering. I am new in Kwant and, for this reason, I'm trying to use Kwnat for basic problems of scattering. The most simple problem in my mind is the scattering of a plane-wave (1 dimension) from the left of a potential barrier. If we now suppose the potential barrier is 'zero' everywhere, the scattering matrix, according to the scattering theory, should be 'S={{0,1},{1,0}}'. If I try to compute the reflection and transmission coefficient, I obtained the correct values (1 for reflection and 0 for transmission). But it occurs only for some energies. For example in the code I attached, if I put the value of '10' in 'S=kwant.solvers.default.smatrix(syst,10)' I obtaine for reflection and transmission the value of '0'. Where is my errors? And, is there a way to print the entire elements of the scattering matrix ? Yours sincerely Lorenzo Bagnasacco

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Re: How to get Kwant plot data for other use?
by Ajit Kumar Sahu Jan. 18, 2022

Jan. 18, 2022

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Add -fPIC flag to linker
by Etienne Fayen Jan. 18, 2022

Jan. 18, 2022

Dear kwant user, I am trying to build kwant and its dependencies from sources. A first build without Mumps succeeded. When adding Mumps however, the linker returns the following error: /usr/bin/ld: /opt/mumps-5.4.1/lib/libzmumps.a(ztools.o): relocation R_X86_64_PC32 against symbol `.gomp_critical_user_critical_old_ooc' can not be used when making a shared object; recompile with -fPIC /usr/bin/ld: final link failed: bad value Here is the content of the build.conf [mumps] include_dirs = /opt/mumps-5.4.1/include /opt/scotch-7.0/include library_dirs = /opt/mumps-5.4.1/lib /opt/mumps-5.4.1/libseq /opt/scotch-7.0/lib libraries = zmumps mumps_common pord esmumps scotch scotcherr mpiseq gfortran Would adding -fPIC flag as suggested by the error message solve the issue ? If so, how can this flag be added with the python build setup ? Best, Etienne F

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How to get Kwant plot data for other use?
by sahu.ajit92＠gmail.com Jan. 10, 2022

Jan. 10, 2022

Dear all, I am new to kwant. I want numerical data from Kwant for e.g. numerical data that is used to plot the honeycomb structure. Thanking you Ajit Kumar Sahu

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Problems in calculating conductivity using the KPM method
by 674657065＠qq.com Jan. 7, 2022

Jan. 7, 2022

Dear all： I am a PHD student and i am using the kwant to calculate the conductivity of the graphene. Excuse me, I'd like to ask you a question that in the kwant documentation, you used the KPM method to calculate the conductivity of graphene. Does the disorder strength take a value of 0 or approach 0? If the disorder strength is 0, why is the conductivity not diverging at points where the energy is not zero? Thank you for your answer. Best wishes Hanlin Liu

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