Search found 12 matches
- 26 Mar 2019, 07:29
- Forum: HowTos and FAQ for TeNPy
- Topic: Performing TEBD for NNN interactions
- Replies: 1
- Views: 3287
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...
- 01 Mar 2019, 08:41
- Forum: HowTos and FAQ for TeNPy
- Topic: Product state results
- Replies: 3
- Views: 5548
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...
- 26 Feb 2019, 07:18
- Forum: HowTos and FAQ for TeNPy
- Topic: Product state results
- Replies: 3
- Views: 5548
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...
- 26 Feb 2019, 07:11
- Forum: HowTos and FAQ for TeNPy
- Topic: Exponentiation of operator / String order parameter
- Replies: 11
- Views: 109695
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?
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?
- 22 Feb 2019, 09:17
- Forum: HowTos and FAQ for TeNPy
- Topic: Exponentiation of operator / String order parameter
- Replies: 11
- Views: 109695
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 ...
- 22 Feb 2019, 08:20
- Forum: HowTos and FAQ for TeNPy
- Topic: Exponentiation of operator / String order parameter
- Replies: 11
- Views: 109695
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 ...
- 21 Feb 2019, 09:12
- Forum: HowTos and FAQ for TeNPy
- Topic: Exponentiation of operator / String order parameter
- Replies: 11
- Views: 109695
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...
- 01 Feb 2019, 07:48
- Forum: Algorithms
- Topic: Some questions about DMRG
- Replies: 2
- Views: 15936
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...
- 31 Jan 2019, 09:56
- Forum: Algorithms
- Topic: Some questions about DMRG
- Replies: 2
- Views: 15936
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 ...
- 29 Aug 2018, 07:28
- Forum: HowTos and FAQ for TeNPy
- Topic: Different coupling terms on different sites
- Replies: 5
- Views: 11936
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...
- 28 Aug 2018, 05:36
- Forum: HowTos and FAQ for TeNPy
- Topic: Different coupling terms on different sites
- Replies: 5
- Views: 11936
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...
- 27 Aug 2018, 09:39
- Forum: HowTos and FAQ for TeNPy
- Topic: Different coupling terms on different sites
- Replies: 5
- Views: 11936
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 ...