Search found 21 matches

by dorf
27 Jun 2022, 03:28
Forum: HowTos and FAQ for TeNPy
Topic: term_correlation_function_left for MPSEnvironment
Replies: 0
Views: 20

term_correlation_function_left for MPSEnvironment

Hi, I want to calculate the expectation value \langle \psi| S_i^z S_{i+1}^z |\phi \rangle . Because the two MPS are different, I create a tenpy.networks.mps.MPSEnvironment . What is the best way to compute the above correlation function? For tenpy.networks.mps.MPS there is tenpy.networks.mps.MPS.ter...
by dorf
27 Jun 2022, 03:05
Forum: HowTos and FAQ for TeNPy
Topic: add_multi_coupling vs. GroupedSite
Replies: 4
Views: 182

Re: add_multi_coupling vs. GroupedSite

You are right. I only benchmarked up to ~256 where it wasn't so significant.
Thanks again, for the input!
by dorf
16 Jun 2022, 05:27
Forum: HowTos and FAQ for TeNPy
Topic: add_multi_coupling vs. GroupedSite
Replies: 4
Views: 182

Re: add_multi_coupling vs. GroupedSite

Thank you very much for the answer. I implemented both and the results match. The difference in computation time was not so significant (for now), so I might stick to grouped sites because, as you said, they are kind of 'prettier' and easier to handle when extracting correlation functions etc. Again...
by dorf
23 May 2022, 04:37
Forum: HowTos and FAQ for TeNPy
Topic: add_multi_coupling vs. GroupedSite
Replies: 4
Views: 182

add_multi_coupling vs. GroupedSite

Hello, I have a unit cell with 2 FermionSite and I would like to implement a term like c^\dagger_{0, n+1}c^\dagger_{1, n+1}c_{1, n}c_{0, n} , where 0 and 1 are the sublattice indices and n runs over the unit cells. So something like a two-body hopping term (or can be thought of as a nearest neighbor...
by dorf
10 Dec 2021, 13:32
Forum: HowTos and FAQ for TeNPy
Topic: Periodic versus Open Boundary Conditions
Replies: 5
Views: 1211

Re: Periodic versus Open Boundary Conditions

Thank you very much for the quick update! I managed to reproduce the results with open boundary conditions for the 'folded' ladder, by reordering the expectations value. Next step is to try it out with the periodic boundary conditions. In the post you refer to you you write that you should set [tenp...
by dorf
08 Dec 2021, 13:23
Forum: HowTos and FAQ for TeNPy
Topic: Periodic versus Open Boundary Conditions
Replies: 5
Views: 1211

Re: Periodic versus Open Boundary Conditions

Dear Johannes,
Sorry, I had put this problem aside for a while. Anyway, thank you very much for your answer.

The 'folded' order is not yet implemented for the ladder system, right? Can I implement a custom order myself in the model that I built?

Best,
Niclas
by dorf
27 Oct 2021, 07:35
Forum: HowTos and FAQ for TeNPy
Topic: Periodic versus Open Boundary Conditions
Replies: 5
Views: 1211

Periodic versus Open Boundary Conditions

Hello, I want to compare a finite system that has a surface with it's 'bulk-counterpart'. Using first DMRG calculations and then time-evolving methods I calculated the excitation spectrum. The size of the finite system was large enough, and it worked out well. However, now I want to compare it to th...
by dorf
30 Aug 2021, 19:42
Forum: HowTos and FAQ for TeNPy
Topic: M1 compatibily
Replies: 1
Views: 739

M1 compatibily

I recently switched to a computer running Apples new M1 chip. However, tenpy is not available for the M1 conda distribution. Should I just run it via Rosetta (Apple's Intel interface) or can we expect a M1 compatible package on conda any time soon? :)
by dorf
28 Jun 2021, 14:56
Forum: HowTos and FAQ for TeNPy
Topic: Custom (sum of) Operators
Replies: 3
Views: 1392

Re: Custom (sum of) Operators

Thank you very much for your reply and that new functionality! However, I didn't quite get how to construct the operator for two different sites. Reading the documentation it seems that I have to pass an array of strings to kron(), which will be translated into some local operators (e.g. 'Sz' for th...
by dorf
21 Apr 2021, 08:52
Forum: HowTos and FAQ for TeNPy
Topic: Custom (sum of) Operators
Replies: 3
Views: 1392

Custom (sum of) Operators

Hi, is there an easy way to make custom operators and apply them to a MPS via 'mps.apply_local_op()'? Let's say I want to apply S^x_i + S^y_i+1 - const*Id. Is there some functionality that I can construct this operator, give a name to it, and then apply it? The 'const' is evaluated at runtime, so de...
by dorf
02 Apr 2021, 12:54
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 4931

Re: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

Thank you very much for the additional information. This is super helpful! Best regards!
by dorf
01 Apr 2021, 18:49
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 4931

Re: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

Dear Johannes, thank you very much for your help. For the moment I'm fine working with finite systems, as well. I mostly started with iDMRG because I followed the rough description given in Sec. IV in this work: https://arxiv.org/pdf/1804.06811.pdf it is explicitly mentioned that an iDMRG ground sta...
by dorf
01 Apr 2021, 10:35
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 4931

Re: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

So after a couple of tests, the problem described above persists to occur for many combinations of states. At each time point t of the evolution I want to initialize an MPSEnvironment for all j for <psi_0 | psi_j> with |psi_j> being the time evolved state at time t with |psi_j> = U S_j |psi_0>, to t...
by dorf
27 Mar 2021, 12:00
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 4931

Re: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

Sorry for my late reply, I really appreciate the help. Below you find the traceback, after I called MPSEnvironment(psi_0, testpsi) with psi_0 being an iDMRG ground state to which applied 'Sz' to some site with mps.apply_local_op, and testpsi the output of ExpMPOEvolution where psi_0.apply_local_op(s...
by dorf
23 Mar 2021, 19:16
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 4931

Re: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

Thank you very much for the answer. I calculated the time evolution for a t that provides me with a sufficient frequency resolution (for first tests in any case). However, I’m still concerned with the technicality that I mentioned above that I get the Error ‘incompatible leg charge’ when I want to c...
by dorf
23 Mar 2021, 12:47
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 4931

Re: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

So I guess the problem is that the maximal bond dimensions of the iDMRG ground state psi_0, and the time evolved ground state psi are different. I passed the same chi_max to both algorithms, but since psi_0 is closer to a product state it doesn't need a very high chi. Is there a way to 'grow' psi_0 ...
by dorf
15 Mar 2021, 11:40
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 4931

Re: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

Quick Follow-up question: So I guess the code to obtain the structure factor C^zz_ij could look something like this (already having calculated the iDMRG ground state psi_0): C_ij = [] for site in range(num_sites): # apply the first operator to the ground state psi = psi_0.copy() psi.apply_local_op(s...
by dorf
12 Mar 2021, 00:16
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 4931

Re: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

Thanks a lot. I was a little overwhelmed with the many possibilities, but I settled on trying out ExpMPOEvolution.
In the last step, why should I use mpsenvironment.expectation_value instead of the mps.method?
by dorf
09 Mar 2021, 13:49
Forum: HowTos and FAQ for TeNPy
Topic: Fourier Transform Product state
Replies: 1
Views: 1045

Fourier Transform Product state

Within some approximation a system has the ground state |\tilde{\psi}_0 \rangle and an excited state |\tilde{\psi}_1 \rangle = \hat{O}|\tilde{\psi}_0 \rangle that is connected via the operator \hat{O} , which is known. I now did a DMRG calculation for that system, obtaining the real ground state |\p...
by dorf
16 Feb 2021, 17:12
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 4931

Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

Hello, I would like to calculate the Dynamical Spin Structure and/or the Excitation spectrum of the 2 chain spin ladder, which I implemented below.Ultimately, I would like to compare the results to Neutron Scattering experiments. Using the ladder lattice of TenPy I constructed the model: class spinL...