Search found 26 matches

by bart
15 Dec 2020, 14:40
Forum: HowTos and FAQ for TeNPy
Topic: Bosonic Haldane Model
Replies: 2
Views: 2480

Re: Bosonic Haldane Model

Thanks for spotting this and apologies for the slow reply. The will have consequences for any case where the chemical potential is non-zero. This does not effect the example default parameters but it's good that it's fixed now.
by bart
14 Jun 2019, 15:50
Forum: HowTos and FAQ for TeNPy
Topic: DMRG sweep problems
Replies: 5
Views: 5700

Re: DMRG sweep problems

I am also having convergence problems getting the FCI phase from arxiv:1407.6985 . I have tried it for bosons, every permutation of the initial product state, different system sizes, with/without mixer, etc. Without interaction everything works fine for me, and I get the same figures as in the paper...
by bart
07 May 2019, 14:07
Forum: HowTos and FAQ for TeNPy
Topic: add_coupling in SpinModel
Replies: 4
Views: 4338

Re: add_coupling in SpinModel

Thank you for the clarification, and tips for further speedup! It's helpful to know that I am roughly on the right lines with this now. Thanks again :D
by bart
07 May 2019, 11:02
Forum: HowTos and FAQ for TeNPy
Topic: add_coupling in SpinModel
Replies: 4
Views: 4338

Re: add_coupling in SpinModel

Thank you for quick reply and explanation - this makes sense and is surely correct. I was trying to implement a more complicated Hamiltonian, which then made me generally confused... :oops: I am looking at a Hamiltonian of the form: H = J \sum_{<i,j>}\sum_{a,b=1}^3 T^{ab}_i T^{ab}_j where \sigma^a a...
by bart
06 May 2019, 13:02
Forum: HowTos and FAQ for TeNPy
Topic: add_coupling in SpinModel
Replies: 4
Views: 4338

add_coupling in SpinModel

I am not sure how the add_couplings in ``models/spins.py`` are constructed (for the Jx and Jy terms). When I use the substitutions S^\pm=S^x \pm \mathrm{i} S^y , I get: J_x S^x_i S^x_j + J_y S^y_i S^y_j = \left( \frac{J_x + J_y}{4} \right)(S^+_i S^-_j + S^-_i S^+_j) + \left( \frac{J_x - J_y}{4} \rig...
by bart
24 Apr 2019, 07:26
Forum: HowTos and FAQ for TeNPy
Topic: norm_tol parameter for DMRG
Replies: 2
Views: 8023

norm_tol parameter for DMRG

I am searching for a way to reliably get rid of the warning: /TeNPy/tenpy/algorithms/dmrg.py:523: UserWarning: final DMRG state not in canonical form within `norm_tol` = 1.00e-06 warnings.warn(msg.format(nt=norm_tol)) I have tried running a simulation with the following DMRG parameters: dmrg_params ...
by bart
24 Apr 2019, 06:56
Forum: HowTos and FAQ for TeNPy
Topic: Interpenetrating Lattices
Replies: 2
Views: 2946

Re: Interpenetrating Lattices

Thank you for the quick reply, and the example with plot is much appreciated! :D
by bart
24 Apr 2019, 06:42
Forum: Implementations
Topic: Triangular Lattice
Replies: 4
Views: 11967

Re: Triangular Lattice

Thank you very much! :D
by bart
18 Apr 2019, 14:53
Forum: Implementations
Topic: Triangular Lattice
Replies: 4
Views: 11967

Re: Triangular Lattice

Using this basis, for a point at the origin: There are 6 NN at a distance 1. There are 6 nNN at a distance sqrt(3). There are 6 nnNN at a distance 2. NN = {1/2 {Sqrt[3], 1}, {0, 1}, -(1/2) {Sqrt[3], 1}, -{0, 1}, 1/2 {Sqrt[3], -1}, 1/2 {-Sqrt[3], 1}}; nNN = {{Sqrt[3], 0}, {-Sqrt[3], 0}, 1/2 {Sqrt[3],...
by bart
18 Apr 2019, 14:12
Forum: HowTos and FAQ for TeNPy
Topic: Interpenetrating Lattices
Replies: 2
Views: 2946

Interpenetrating Lattices

What is the best way to implement interpenetrating lattices in TeNPy? Simple example: a square lattice with alternating one-orbital GroupedSite and three-orbital GroupedSite (like a checkerboard). Or, alternatively, a honeycomb lattice with a triangular lattice on top (where the triangular lattice i...
by bart
18 Apr 2019, 12:44
Forum: Implementations
Topic: Triangular Lattice
Replies: 4
Views: 11967

Triangular Lattice

It would be useful to have an implementation for a triangular lattice integrated into the main code (tenpy.models.lattice), since it comes up so frequently. Many thanks :)
by bart
19 Feb 2019, 08:08
Forum: HowTos and FAQ for TeNPy
Topic: Interpretation of qnumber>1 for Entanglement Spectra
Replies: 3
Views: 3839

Re: Interpretation of qnumber>1 for Entanglement Spectra

Thank you for the clarification and for making me aware of the chinfo attribute, so that I can double-check the qnumbers myself. This has answered my question - thanks again! :)
by bart
18 Feb 2019, 08:49
Forum: HowTos and FAQ for TeNPy
Topic: Interpretation of qnumber>1 for Entanglement Spectra
Replies: 3
Views: 3839

Re: Interpretation of qnumber>1 for Entanglement Spectra

UPDATE: I have noticed that when I use a model with spinless fermions, there is only one qnumber instead of two (as for fermions with spin). Does this mean that the second qnumber had something to do with spin? Do these qnumbers originate from the conserved quantities that I specify in model_params?...
by bart
14 Feb 2019, 16:04
Forum: HowTos and FAQ for TeNPy
Topic: Twisted Boundary Conditions for a CouplingMPOModel
Replies: 3
Views: 4361

Twisted Boundary Conditions for a CouplingMPOModel

I would like to plot spectral flow plots similar to Fig.2.b)/d) of this paper https://arxiv.org/abs/1407.6985 Fig2.png Quote about implementation of Fig.2.b)/d) from the paper: The flux \Phi_y threading through the cylinder is implemented in the MPO Hamiltonian by twisting the boundary conditions su...
by bart
14 Feb 2019, 15:42
Forum: HowTos and FAQ for TeNPy
Topic: Interpretation of qnumber>1 for Entanglement Spectra
Replies: 3
Views: 3839

Interpretation of qnumber>1 for Entanglement Spectra

I would like to plot an entanglement spectrum similar to Fig.3.b) of this paper https://arxiv.org/abs/1407.6985 Fig3.png Quote about the coloring of Fig.3.b): The entanglement spectrum can be resolved further into distinct U(1) charge sectors Q_{\alpha}^L\in \mathbb{Z} where Q_{\alpha}^L label the U...
by bart
14 Feb 2019, 10:20
Forum: HowTos and FAQ for TeNPy
Topic: Scaling of entanglement entropy for iDMRG
Replies: 7
Views: 6893

Re: Scaling of entanglement entropy for iDMRG

Hi Umberto, thank you for the reply and for the useful link! I hadn't seen that paper before, but it does suggest that the original formula was correct after all. In which case, I wonder why I cannot reproduce it... I am trying in the most naive way using the example_DMRG_infinite(g=1.) function fro...
by bart
14 Feb 2019, 09:28
Forum: HowTos and FAQ for TeNPy
Topic: Investigations of the Hubbard model
Replies: 2
Views: 3944

Re: Investigations of the Hubbard model

Thank you for confirming the general set-up and for making me suspicious of my \chi -value :lol: I will check my results for convergence with a larger \chi when I have more compute time available. The middle two questions were in a way connected because the vast majority of results in the literature...
by bart
14 Feb 2019, 08:06
Forum: HowTos and FAQ for TeNPy
Topic: perm parameter in compute_K function
Replies: 2
Views: 11288

Re: perm parameter in compute_K function

Thank you for the clarification! :) In that case, I will use the following:

Code: Select all

psi.compute_K(perm=M.lat)  # where M is your model
Thank you for explaining how this works, and for the "verbose=2" tip to check that everything is being permuted as it should.
by bart
05 Feb 2019, 11:17
Forum: HowTos and FAQ for TeNPy
Topic: perm parameter in compute_K function
Replies: 2
Views: 11288

perm parameter in compute_K function

What is the correct way to define perm in the compute_K function? I know that the wave function should be invariant under the rotation/permutation and so I need to check that the ov returned by compute_K is close to one. However, I am not sure how to define the correct permutation. e.g. for an initi...
by bart
31 Jan 2019, 16:10
Forum: HowTos and FAQ for TeNPy
Topic: Investigations of the Hubbard model
Replies: 2
Views: 3944

Investigations of the Hubbard model

I am in the process of testing the spin-1/2 Fermi-Hubbard model on a square lattice (infinite cylinder) with Hamiltonian: H = \sum_{\langle i, j \rangle, i < j, \sigma} t (c^{\dagger}_{\sigma, i} c_{\sigma j} + \text{H.c.}) + \sum_i U n_{\uparrow, i} n_{\downarrow, i} , where \langle i, j \rangle, i...
by bart
30 Jan 2019, 13:32
Forum: HowTos and FAQ for TeNPy
Topic: How to generate a random MPS in tenpy
Replies: 5
Views: 6772

Re: How to generate a random MPS in tenpy

I'm not sure exactly which type of random MPS you're looking for, however for a spin-1/2 example, I would do something like this to generate a random initial product state: product_state = [] for i in range(M.lat.N_sites): product_state.append(random.choice(["up", "down"])) psi =...
by bart
29 Jan 2019, 16:15
Forum: HowTos and FAQ for TeNPy
Topic: Scaling of entanglement entropy for iDMRG
Replies: 7
Views: 6893

Re: Scaling of entanglement entropy for iDMRG

Ah I see, that is also consistent with what I have read in the literature here: https://arxiv.org/abs/0712.1976 Thank you for the clarification! :-) So, from this, I conclude that Frank Pollmann must have made a mistake in exercise 3.3 of this sheet http://quantumtensor.pks.mpg.de/wp-content/uploads...
by bart
29 Jan 2019, 15:16
Forum: HowTos and FAQ for TeNPy
Topic: Scaling of entanglement entropy for iDMRG
Replies: 7
Views: 6893

Re: Scaling of entanglement entropy for iDMRG

Thank you very much for your quick reply and the references! Do you mean that the formula that I wrote doesn't apply to iDMRG, or that I did not implement the boundary conditions correctly? Am I correct in understanding that you are using these terms interchangeably: infinite system <=> periodic bou...
by bart
29 Jan 2019, 10:11
Forum: HowTos and FAQ for TeNPy
Topic: Scaling of entanglement entropy for iDMRG
Replies: 7
Views: 6893

Scaling of entanglement entropy for iDMRG

I have read in the literature that the following relation should hold for iDMRG: S=\frac{c}{6}\log\xi , where c=\frac{1}{2} for the TF Ising model (at the critical point g/J=1 ). However, when I try to plot the entanglement entropy against correlation length using the "examples/d_dmrg.py" ...
by bart
25 Jan 2019, 15:17
Forum: HowTos and FAQ for TeNPy
Topic: xxz_corrlength.py example gives error 'out of the box'
Replies: 2
Views: 3216

Re: xxz_corrlength.py example gives error 'out of the box'

Oh great, I'm glad that it was something simple like that. Thank you for the clarification and fix! :-)