Search found 12 matches

by on0001st
26 Mar 2019, 07:29
Forum: HowTos and FAQ for TeNPy
Topic: Performing TEBD for NNN interactions
Replies: 1
Views: 2744

Performing TEBD for NNN interactions

Hi, I would like to perform TEBD for a spin system that contains NNN interactions. I see that there is already a function "swap_sites" defined in mps.py which I think it is closely related to the swap gates method. However, I am no entire sure how to implement it properly. My naive hunch t...
by on0001st
01 Mar 2019, 08:41
Forum: HowTos and FAQ for TeNPy
Topic: Product state results
Replies: 3
Views: 3958

Re: Product state results

Thanks for your reply Qicheng! I have seen your post and I think what I mean by random here is different from what you needed. I would say the "random" state that I mean here is simply a random product state, i.e., a random sequence of spin ups and downs for spin half as opposed to a initi...
by on0001st
26 Feb 2019, 07:18
Forum: HowTos and FAQ for TeNPy
Topic: Product state results
Replies: 3
Views: 3958

Product state results

Sometimes when using tenpy DMRG class, the final result produced from the dmrg is a product state. I believe this is the case as all of the bond dimensions are 1. There are times when this is the right result but sometimes it is not too. I was wondering what is the reason that DMRG converges to this...
by on0001st
26 Feb 2019, 07:11
Forum: HowTos and FAQ for TeNPy
Topic: Exponentiation of operator / String order parameter
Replies: 11
Views: 58462

Re: Exponentiation of operator / String order parameter

Thank you so much for the help!

Other than by extracting Sz from the site class, is it possible to code up Sz explicitly and then convert it into a np_conserved array? What would be the proper procedure for it?
by on0001st
22 Feb 2019, 09:17
Forum: HowTos and FAQ for TeNPy
Topic: Exponentiation of operator / String order parameter
Replies: 11
Views: 58462

Re: Exponentiation of operator

Ah okay! So I have been trying to implement the matrix exponentiation for the correlation_function function but I am still facing some difficulties. When I try to use either scipy.linalg.expm('Sz') or tenpy.linalg.np_conserved.npc('Sz') directly, I get 'str' object has no attribute 'rank'. Yet when ...
by on0001st
22 Feb 2019, 08:20
Forum: HowTos and FAQ for TeNPy
Topic: Exponentiation of operator / String order parameter
Replies: 11
Views: 58462

Re: Exponentiation of operator

Thank you so much for the help, expm is exactly what I was looking for! I was also suspecting what I wrote to be slightly wrong but I was not sure, hence I posted it here to double check. I am a little bit confused with Moreover, let me note that if you look at Spin-1/2, choosing B_k=exp⁡(iπS_z) is ...
by on0001st
21 Feb 2019, 09:12
Forum: HowTos and FAQ for TeNPy
Topic: Exponentiation of operator / String order parameter
Replies: 11
Views: 58462

Exponentiation of operator / String order parameter

I am trying to calculate string order parameter and I was wondering how should I go about doing it? I have tried looking through model.py, sites.py and charges.py but I do not see a clear way to exponentiate the operators for the calculation of the expectation values. My idea was to do something lik...
by on0001st
01 Feb 2019, 07:48
Forum: Algorithms
Topic: Some questions about DMRG
Replies: 2
Views: 10284

Re: Some questions about DMRG

Thank you for the detailed reply, Johannes. It really helps a lot. The gap that I am talking about is a finite size gap due to finite size effects. Generally, one would expect this to decrease to the actual gap size as we approach the thermodynamic limit. In the case of what I am looking at, the sys...
by on0001st
31 Jan 2019, 09:56
Forum: Algorithms
Topic: Some questions about DMRG
Replies: 2
Views: 10284

Some questions about DMRG

Hi, I would like to clarify questions about DMRG. Am I right to say that DMRG works very well for gapped Hamiltonians because of the area law and the fact that entanglement in the ground states of such Hamiltonians are minimised? When we extend the method to gapless Hamiltonians, as gapless systems ...
by on0001st
29 Aug 2018, 07:28
Forum: HowTos and FAQ for TeNPy
Topic: Different coupling terms on different sites
Replies: 5
Views: 10112

Re: Different coupling terms on different sites

In fact, for finite systems, you can just use MPOEnvironment(psi, H, psi).full_contraction(). Yes, this was what I was wondering how it can be done. I see in the method of full contraction that there is a need to specify a site index. As we are contracting the entire MPS to calculate for energy, is...
by on0001st
28 Aug 2018, 05:36
Forum: HowTos and FAQ for TeNPy
Topic: Different coupling terms on different sites
Replies: 5
Views: 10112

Re: Different coupling terms on different sites

Thank you so much for the swift reply! I have pulled the latest git commit and am able to run the code using spinChainNNN2. However, as not it is not a nearest neighbour model, I am not able to to use the method of E = np.sum(psi.expectation_value(M.H_bond[1:])) to calculate the energies. I have tri...
by on0001st
27 Aug 2018, 09:39
Forum: HowTos and FAQ for TeNPy
Topic: Different coupling terms on different sites
Replies: 5
Views: 10112

Different coupling terms on different sites

Hi all, I am trying to implement a DMRG calculation using the spin_nnn model with the coupling term being different on different sites. To my understanding, we can do this for magnetic fields by defining a list with the different magnetic fields for different sites and passing the list as the model ...