Mailman 3 September 2021 - Kwant-discuss

Calculate conductivity of 3D periodic boundary condition system with disorder
by Jerry xhm 26 Sep '21

26 Sep '21

Hello, I am thinking of calculating the conductivity with Kwant's KPM method of a 3D system with disorder and periodic boundary conditions (PBC) in every direction (no leads). Reading some old posts, it seems to be some problem with multiple translational symmetries (or PBCs?). In my case, because of adding disorder potential, I only want PBC rather than translational symmetry. So I presume the wraparound module is irrelevant here. Is that possible and if any problem when further calculating its conductivity? Naively we only need to manually add hoppings that 'wrap around' the lattice. Does this cause any problem in Kwant and is there any good practice/trick for this? Thank you!

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How to caculate hall resistance
by ZHANG Bing 12 Sep '21

12 Sep '21

Dear Sir, I am a PhD student of Hong Kong University of Science and Technology. I want to use KWANT to caculate Hall resistance of a Hall bar structure.We can get the conductance between 6 electrodes, but how to get hall resistance? Can you give me some help? Thank you very much. Best Regards, Zhang Bing

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Difference of Haldane model
by njudyp＠sina.com 08 Sep '21

08 Sep '21

Dear Kwant authors I am Yongping Du from Nanjing University of Science and Technology. I have been using the KPM method to calculate the transport properties of various graphene nanostructures, together with Prof. A. P. Jauho. As a benchmark, I calculated the conductance and density of states of the Haldane model. To my surprise, I found some differences between my numerical results and the ones obtained with Kwant. I carefully checked every term of Haldane model in my implementation and found that the hopping direction of two next nearest neighbor hopping terms was the key to those differences. By reversing the direction of the hopping term in my program, I could reproduce the results from Kwant. However, I can find no physical justification for this change. I would be most grateful if you can help me to remove this discrepancy. Best regards Yongping Du

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Computation time scaling for dimensions other than two?
by xiaoxiao.zhang＠riken.jp 02 Sep '21

02 Sep '21

Hello Kwant Community, In the 2014 kwant paper New J. Phys. 16 063065, Fig. 6 gives the conductance computation time scaling for 2D systems of side length L: O(L^2) for construction, O(L^3) for solving with the MUMPS-based solver, and O(L^4) for solving with RGF. I was wondering what the general scaling is for other dimensions. I presume it is known to experts and might be helpful to many users. Thank you.

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module 'kwant.linalg._mumps' has no attribute 'dmumps' ERROR
by BHAVYA BHARDWAJ 02 Sep '21

02 Sep '21

Repected Members, I am a B.Tech Student using Kwant for simulations.Python Version: 3.7.8 Kwant Version: 1.4.2Ubuntu 20The Error I faced is given below. AttributeError Traceback (most recent call last) <ipython-input-6-c80da766c4bb> in <module> 17 pyplot.ylabel("conductance [e^2/h]") 18 pyplot.show() ---> 19 solving(model.tokwant()) <ipython-input-6-c80da766c4bb> in solving(sys) 7 energy = ie * 0.01 8 # compute the scattering matrix at a given energy ----> 9 smatrix = kwant.greens_function(sys, energy,check_hermiticity=False) 10 # compute the transmission probability from lead 0 to 11 # lead 1 ~/Downloads/112358/lib/python3.7/site-packages/kwant/_common.py in inner(*args, **kwargs) 70 if sig.bind(*args, **kwargs).arguments.get(parameter_name): 71 warn() ---> 72 return f(*args, **kwargs) 73 74 return inner ~/Downloads/112358/lib/python3.7/site-packages/kwant/solvers/common.py in greens_function(self, sys, energy, args, out_leads, in_leads, check_hermiticity, params) 485 rhs = sp.bmat([[i for i in linsys.rhs if i.shape[1]]], 486 format=self.rhsformat) --> 487 flhs = self._factorized(linsys.lhs) 488 data = self._solve_linear_sys(flhs, rhs, kept_vars) 489 ~/Downloads/112358/lib/python3.7/site-packages/kwant/solvers/mumps.py in _factorized(self, a) 102 def _factorized(self, a): 103 inst = mumps.MUMPSContext() --> 104 inst.factor(a, ordering=self.ordering) 105 return inst 106 ~/Downloads/112358/lib/python3.7/site-packages/kwant/linalg/mumps.py in factor(self, a, ordering, ooc, pivot_tol, reuse_analysis, overwrite_a) 318 row, col, data) 319 else: --> 320 self.analyze(a, ordering=ordering, overwrite_a=overwrite_a) 321 322 self.mumps_instance.icntl[22] = 1 if ooc else 0 ~/Downloads/112358/lib/python3.7/site-packages/kwant/linalg/mumps.py in analyze(self, a, ordering, overwrite_a) 227 228 if dtype != self.dtype: --> 229 self.mumps_instance = getattr(_mumps, dtype+"mumps")(self.verbose) 230 self.dtype = dtype 231 AttributeError: module 'kwant.linalg._mumps' has no attribute 'dmumps' Kindly guide me so I can overcome this error. Thank You, Regards, Bhavya Bhardwaj

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