# Latest **URL:** https://itensor.discourse.group/latest.md [Latest](https://itensor.discourse.group/latest.md) · [Categories](https://itensor.discourse.group/categories.md) · [Tags](https://itensor.discourse.group/tags.md) --- ## [Please Read: Make It Easier to Help You](https://itensor.discourse.group/t/please-read-make-it-easier-to-help-you/7)
**Author:** [@system](https://itensor.discourse.group/u/system)\ **Replies:** 0\ **Last updated:** [March 30, 2022, 10:43am UTC](https://itensor.discourse.group/t/please-read-make-it-easier-to-help-you/7 "2022-03-30T10:43:56Z")
This community is for technical support and discussion of the ITensor Software, and official packages based on ITensor. We highly recommend using the Julia version of ITensor. It has the same or better performance compa… --- ## [\[BUG\] Repeated HDF5 read of MPS becomes increasingly slow, apparently related to GC](https://itensor.discourse.group/t/bug-repeated-hdf5-read-of-mps-becomes-increasingly-slow-apparently-related-to-gc/2639)
**Author:** [@JBTouchais](https://itensor.discourse.group/u/JBTouchais)\ **Replies:** 0\ **Last updated:** [September 22, 2026, 6:37am UTC](https://itensor.discourse.group/t/bug-repeated-hdf5-read-of-mps-becomes-increasingly-slow-apparently-related-to-gc/2639 "2026-09-22T06:37:54Z")
Description of issue : Repeated use of HDF5.write(parent::Union{HDF5.File, HDF5.Group}, name::AbstractString, M::MPS) or HDF5.read(parent::Union{HDF5.File, HDF5.Group}, name::AbstractString, ::Type{MPS}) on the same file… --- ## [How do you make projective measurements?](https://itensor.discourse.group/t/how-do-you-make-projective-measurements/1831)
**Author:** [@acroscarrillo](https://itensor.discourse.group/u/acroscarrillo)\ **Replies:** 8\ **Last updated:** [September 21, 2026, 2:12pm UTC](https://itensor.discourse.group/t/how-do-you-make-projective-measurements/1831 "2026-09-21T14:12:14Z")
Quick summary of my question: Beginner here looking to simulate a time evolution of an initial state with low entanglement to which local projective measurements, not expectation values, are applied. I know how to do t… --- ## [Where should I start learning iTensor as a beginner?](https://itensor.discourse.group/t/where-should-i-start-learning-itensor-as-a-beginner/2637)
**Author:** [@MHSZ](https://itensor.discourse.group/u/MHSZ)\ **Replies:** 1\ **Last updated:** [September 11, 2026, 12:34am UTC](https://itensor.discourse.group/t/where-should-i-start-learning-itensor-as-a-beginner/2637 "2026-09-11T00:34:59Z")
Hi everyone, I’m a master’s student studying Quantum Computing and Quantum Information. My semester starts in about 10 days, and I’d like to get a head start on learning iTensor. I spoke with my advisor, and they recom… --- ## [time dependent correlators with electrons](https://itensor.discourse.group/t/time-dependent-correlators-with-electrons/2630)
**Author:** [@Leon](https://itensor.discourse.group/u/Leon)\ **Replies:** 1\ **Last updated:** [July 24, 2026, 3:26pm UTC](https://itensor.discourse.group/t/time-dependent-correlators-with-electrons/2630 "2026-07-24T15:26:06Z")
Hello there, I did post a related question to this one trying to solve a subsidiary problem. Here I would like to present on what I am failing to implement i.e. to use ITensor properly. I suspect this to be a rather gen… --- ## [Green's function via method:apply(Jordan-wigner..."Cdagup"|0\>)](https://itensor.discourse.group/t/greens-function-via-method-apply-jordan-wigner-cdagup-0/2628)
**Author:** [@Leon](https://itensor.discourse.group/u/Leon)\ **Replies:** 5\ **Last updated:** [July 20, 2026, 12:05pm UTC](https://itensor.discourse.group/t/greens-function-via-method-apply-jordan-wigner-cdagup-0/2628 "2026-07-20T12:05:20Z")
Hello there, I was planning to compute greater and lesser Green’s functions for an tight binding model I was intereseted in. After some try and error, I noticed my implementation was lagging the Jordan Wigner string ope… --- ## [iDMRG package built on ITensors.jl](https://itensor.discourse.group/t/idmrg-package-built-on-itensors-jl/2615)
**Author:** [@zhlphy](https://itensor.discourse.group/u/zhlphy)\ **Replies:** 3\ **Last updated:** [July 3, 2026, 11:12am UTC](https://itensor.discourse.group/t/idmrg-package-built-on-itensors-jl/2615 "2026-07-03T11:12:58Z")
Dear all, I notice a lot of people here are looking for iDMRG in ITensor (so do I). Recently, I have developed one built on ITensors.jl and ITensorMPS.jl: iDMRG It implements: iDMRG using MPS swapping VUMPS (hopeful… --- ## [Obtain 2-nd Renyi negativity without calculating reduce density matrix explicitly.](https://itensor.discourse.group/t/obtain-2-nd-renyi-negativity-without-calculating-reduce-density-matrix-explicitly/2627)
**Author:** [@Wang](https://itensor.discourse.group/u/Wang)\ **Replies:** 0\ **Last updated:** [July 2, 2026, 1:24pm UTC](https://itensor.discourse.group/t/obtain-2-nd-renyi-negativity-without-calculating-reduce-density-matrix-explicitly/2627 "2026-07-02T13:24:24Z")
Hello everyone! I am trying to compute the second-order Renyi negativity E\_2=-\\log(\\text{tr}(ρ\_{AB}^{T\_B})^2/\\text{tr}(ρ²)) of a subsystem from a given MPS wavefunction, based on the framework of ITensorEntropyTools.jl.… --- ## [Large precision error for TDVP of ITensorInfiniteMPS](https://itensor.discourse.group/t/large-precision-error-for-tdvp-of-itensorinfinitemps/2617)
**Author:** [@Zephyr](https://itensor.discourse.group/u/Zephyr)\ **Replies:** 6\ **Last updated:** [July 2, 2026, 9:36am UTC](https://itensor.discourse.group/t/large-precision-error-for-tdvp-of-itensorinfinitemps/2617 "2026-07-02T09:36:10Z")
Hi ITensor teams I’m trying to use ITensorInfniteMPS package to do some real time evolution works. As a test, I try to compute a one step real time evolution for a transverse field Ising model first. I do the subspace e… --- ## [Run on multiple GPUs](https://itensor.discourse.group/t/run-on-multiple-gpus/2626)
**Author:** [@gc6020](https://itensor.discourse.group/u/gc6020)\ **Replies:** 2\ **Last updated:** [June 18, 2026, 6:32am UTC](https://itensor.discourse.group/t/run-on-multiple-gpus/2626 "2026-06-18T06:32:09Z")
Hello everybody, I am running a tensor-network code using ITensors (Julia version) with GPUs (Nvidia A100) on a HPC cluster. I tried to parallelize it to use both GPUs available on a node, but I realized the code is act… --- ## [Left eigenvectors for neon hermitian dmrg](https://itensor.discourse.group/t/left-eigenvectors-for-neon-hermitian-dmrg/2622)
**Author:** [@shuklavaibhav](https://itensor.discourse.group/u/shuklavaibhav)\ **Replies:** 3\ **Last updated:** [June 6, 2026, 4:40pm UTC](https://itensor.discourse.group/t/left-eigenvectors-for-neon-hermitian-dmrg/2622 "2026-06-06T16:40:54Z")
Obtaining the correct left eigenvector of a non-Hermitian Hamiltonian with DMRG Hi everyone, I am trying to compute the biorthogonal entanglement entropy of a non-Hermitian transverse Ising chain using ITensors.jl. The… --- ## [Contracting ITenor with MPO](https://itensor.discourse.group/t/contracting-itenor-with-mpo/2621)
**Author:** [@BenRClark](https://itensor.discourse.group/u/BenRClark)\ **Replies:** 3\ **Last updated:** [June 4, 2026, 3:18pm UTC](https://itensor.discourse.group/t/contracting-itenor-with-mpo/2621 "2026-06-04T15:18:25Z")
Hi all, I am trying to do the contraction Tr(H^\\dagger c\_m^\\dagger H c\_n) where H is an MPO and C and C dagger are fermionic annihilation / creation operators. My problem is I have to the contraction in this order. I… --- ## [Global Subspace Expansion](https://itensor.discourse.group/t/global-subspace-expansion/2619)
**Author:** [@zeqetolaj](https://itensor.discourse.group/u/zeqetolaj)\ **Replies:** 3\ **Last updated:** [May 22, 2026, 10:20pm UTC](https://itensor.discourse.group/t/global-subspace-expansion/2619 "2026-05-22T22:20:08Z")
Hi everyone, I am simulating the real-time dynamics of a 1D Transverse Field Ising Model (TFIM) using 1-site TDVP. The Hamiltonian is given by: H = 4J \\sum\_{j=1}^{N-1} \\hat{S}^z\_j \\hat{S}^z\_{j+1} + 2\\Gamma \\sum\_{j=1}^… --- ## [Anyonic Fermion Model](https://itensor.discourse.group/t/anyonic-fermion-model/2614)
**Author:** [@Jyoti\_Bisht](https://itensor.discourse.group/u/Jyoti_Bisht)\ **Replies:** 1\ **Last updated:** [May 12, 2026, 2:59am UTC](https://itensor.discourse.group/t/anyonic-fermion-model/2614 "2026-05-12T02:59:22Z")
\\hat{H} = -J\\sum\_{j=1}^{N-1} \[\\hat{C}\_{j,\\uparrow}e^{\\iota \\theta\\hat{n}\_{j,\\downarrow}} \\hat{C}\_{j+1,\\uparrow} + \\hat{C}\_{j,\\downarrow}e^{\\iota \\theta\\hat{n}\_{j,\\uparrow}} \\hat{C}\_{j+1,\\downarrow} + h.c.\] Dear ITensor… --- ## [TDVP with time dependent hamiltonian in ITensorMPS.jl v0.4](https://itensor.discourse.group/t/tdvp-with-time-dependent-hamiltonian-in-itensormps-jl-v0-4/2612)
**Author:** [@fgoulette](https://itensor.discourse.group/u/fgoulette)\ **Replies:** 1\ **Last updated:** [May 11, 2026, 4:32pm UTC](https://itensor.discourse.group/t/tdvp-with-time-dependent-hamiltonian-in-itensormps-jl-v0-4/2612 "2026-05-11T16:32:39Z")
Hi everyone, With the release of v0.4 of julia ITensorMPS, TimeDependentSum is no longer available following the removal of the ODE-solver helper infrastructure (see Drop OrdinaryDiffEqTsit5 dependency and ODE-solver he… --- ## [Question About MPO Compression Algorithms in ITensor](https://itensor.discourse.group/t/question-about-mpo-compression-algorithms-in-itensor/2613)
**Author:** [@kevinh](https://itensor.discourse.group/u/kevinh)\ **Replies:** 1\ **Last updated:** [May 8, 2026, 9:38pm UTC](https://itensor.discourse.group/t/question-about-mpo-compression-algorithms-in-itensor/2613 "2026-05-08T21:38:01Z")
Dear ITensor team, I am currently studying MPO compression algorithms, in particular the arXiv paper by Parker, Cao, and Zaletel, Local Matrix Product Operators: Canonical Form, Compression, & Control Theory (arXiv:1909… --- ## [truncate(...; site\_range=j:j+1) and then on j+1:j+2 is not equivalent to truncate(...; site\_range=j:j+2)?](https://itensor.discourse.group/t/truncate-site-range-j-j-1-and-then-on-j-1-j-2-is-not-equivalent-to-truncate-site-range-j-j-2/2611)
**Author:** [@phx](https://itensor.discourse.group/u/phx)\ **Replies:** 4\ **Last updated:** [May 6, 2026, 7:45am UTC](https://itensor.discourse.group/t/truncate-site-range-j-j-1-and-then-on-j-1-j-2-is-not-equivalent-to-truncate-site-range-j-j-2/2611 "2026-05-06T07:45:23Z")
Hi all, I am confused by the following behaviour of the truncate function with respect to the site\_range parameter. Say I have an MPS v, and I want to truncate its 3rd and 4th bonds by setting a maximum bond dimension. … --- ## [METTS seems not to work](https://itensor.discourse.group/t/metts-seems-not-to-work/2609)
**Author:** [@colo4k](https://itensor.discourse.group/u/colo4k)\ **Replies:** 0\ **Last updated:** [April 20, 2026, 9:50pm UTC](https://itensor.discourse.group/t/metts-seems-not-to-work/2609 "2026-04-20T21:50:59Z")
Hello everybody, I tried to code up METTS to estimate thermal expectation values for the Ising mode, by modifying the example code given in the ITensorMPS repository. But I couldn’t get my code to agree with exact diago… --- ## [Question: Build LdagL MPO with symmetries? How to apply DMRG focusing on the real part of the energy?](https://itensor.discourse.group/t/question-build-ldagl-mpo-with-symmetries-how-to-apply-dmrg-focusing-on-the-real-part-of-the-energy/2607)
**Author:** [@Joacop16](https://itensor.discourse.group/u/Joacop16)\ **Replies:** 1\ **Last updated:** [April 20, 2026, 7:49pm UTC](https://itensor.discourse.group/t/question-build-ldagl-mpo-with-symmetries-how-to-apply-dmrg-focusing-on-the-real-part-of-the-energy/2607 "2026-04-20T19:49:52Z")
Hi, ITensor Teams！ For a study of Open Quantum Systems, I need to build L^{\\dagger}L where L is an MPO representation of the Liouvillian Superoperator. In the past, I realized that if I simply used LdagL = apply(dag(L),… --- ## [Is there a way to project a dense MPS into a symmetry sector?](https://itensor.discourse.group/t/is-there-a-way-to-project-a-dense-mps-into-a-symmetry-sector/2608)
**Author:** [@Joacop16](https://itensor.discourse.group/u/Joacop16)\ **Replies:** 0\ **Last updated:** [April 20, 2026, 7:31pm UTC](https://itensor.discourse.group/t/is-there-a-way-to-project-a-dense-mps-into-a-symmetry-sector/2608 "2026-04-20T19:31:34Z")
Hi, ITensor Teams！ First, a little bit of context, for a study in open quantum systems, I need to vectorize the identity: I = \\sum\_{n\_{1}, \\cdots, n\_{N} = { 0,1}} |n\_{1} \\cdots n\_{n} \\rangle \\langle n\_{1} \\cdots n\_{n}… --- ## [Error while calculating out-of-time correlators](https://itensor.discourse.group/t/error-while-calculating-out-of-time-correlators/2603)
**Author:** [@asing](https://itensor.discourse.group/u/asing)\ **Replies:** 5\ **Last updated:** [April 10, 2026, 11:34am UTC](https://itensor.discourse.group/t/error-while-calculating-out-of-time-correlators/2603 "2026-04-10T11:34:50Z")
Hi! In the process of calculating OTOC’s for a spin chain mode, I came across a strange error when I perform backward time evolution. In the following code, I am performing C\_{i1}(i,t) = \\langle \\psi\_{init} | S^z\_i(… --- ## [Exponential of single-site operators with QN](https://itensor.discourse.group/t/exponential-of-single-site-operators-with-qn/2601)
**Author:** [@timothy-ymchan](https://itensor.discourse.group/u/timothy-ymchan)\ **Replies:** 2\ **Last updated:** [April 3, 2026, 5:42pm UTC](https://itensor.discourse.group/t/exponential-of-single-site-operators-with-qn/2601 "2026-04-03T17:42:54Z")
Hi, I have a user-defined site-type as follows: # Reference: https://docs.itensor.org/ITensorMPS/stable/examples/Physics.html # User-defined spin type with Z2xZ2 charge function ITensors.space(::SiteType"Spi… --- ## [How to compute inner product of MPS with another MPS translated by 1 right sites](https://itensor.discourse.group/t/how-to-compute-inner-product-of-mps-with-another-mps-translated-by-1-right-sites/2378)
**Author:** [@JuanD\_H](https://itensor.discourse.group/u/JuanD_H)\ **Replies:** 7\ **Last updated:** [April 3, 2026, 3:43pm UTC](https://itensor.discourse.group/t/how-to-compute-inner-product-of-mps-with-another-mps-translated-by-1-right-sites/2378 "2026-04-03T15:43:42Z")
Hello everyone, I would like to ask if there is a way to compute the inner product ⟨ψ | T₁ | ψ⟩, where T₁ is a cyclic translation operator that shifts site n-to-n+1, by successively applying ITensor’s movesite functions… --- ## [IDMRG for 1-D spin chain](https://itensor.discourse.group/t/idmrg-for-1-d-spin-chain/2599)
**Author:** [@Lee](https://itensor.discourse.group/u/Lee)\ **Replies:** 3\ **Last updated:** [March 31, 2026, 12:27am UTC](https://itensor.discourse.group/t/idmrg-for-1-d-spin-chain/2599 "2026-03-31T00:27:47Z")
Hello, I am not very familiar with directly implementing the iDMRG method. Just for the simplest Heisenberg chain,H = J \\sum\_i \\vec{S}\_i \\cdot \\vec{S}\_{i+1},would it be possible for you to provide a sample Julia script … --- ## [excited states for DMRG in ITensorNetworks](https://itensor.discourse.group/t/excited-states-for-dmrg-in-itensornetworks/2597)
**Author:** [@emile-cochin](https://itensor.discourse.group/u/emile-cochin)\ **Replies:** 2\ **Last updated:** [March 22, 2026, 7:18pm UTC](https://itensor.discourse.group/t/excited-states-for-dmrg-in-itensornetworks/2597 "2026-03-22T19:18:16Z")
Hi, I would like to compute excited states of a given tree Hamiltonian. If I’m not mistaken, there is no option to add ‘penalty states’ in ITensorNetworks.dmrg as there is in the ITensorMPS version? Is there a plan for … --- ## [TDVP for density matrix and local observable expectation value](https://itensor.discourse.group/t/tdvp-for-density-matrix-and-local-observable-expectation-value/2596)
**Author:** [@colo4k](https://itensor.discourse.group/u/colo4k)\ **Replies:** 2\ **Last updated:** [March 19, 2026, 6:27pm UTC](https://itensor.discourse.group/t/tdvp-for-density-matrix-and-local-observable-expectation-value/2596 "2026-03-19T18:27:30Z")
I am new to itensor and would like to use it for my problem but got stuck in how to write an efficient code. I want to time evolve a mixed state using a Hamiltonian and then measure some local observables. I have two que… --- ## [MPO flux not equal when it is symmetric but contains non-zero flux](https://itensor.discourse.group/t/mpo-flux-not-equal-when-it-is-symmetric-but-contains-non-zero-flux/2594)
**Author:** [@ZhouGD2000](https://itensor.discourse.group/u/ZhouGD2000)\ **Replies:** 2\ **Last updated:** [March 9, 2026, 1:33pm UTC](https://itensor.discourse.group/t/mpo-flux-not-equal-when-it-is-symmetric-but-contains-non-zero-flux/2594 "2026-03-09T13:33:48Z")
I would like to act a pair of electron annihilation operator on a state and calculate some properties based on it. Therefore, I create an MPO using the OpSum() and apply it to the MPS I want. However, I find that the obt… --- ## [Time dependent correlation functions with TDVP](https://itensor.discourse.group/t/time-dependent-correlation-functions-with-tdvp/2588)
**Author:** [@zeqetolaj](https://itensor.discourse.group/u/zeqetolaj)\ **Replies:** 4\ **Last updated:** [March 6, 2026, 11:05pm UTC](https://itensor.discourse.group/t/time-dependent-correlation-functions-with-tdvp/2588 "2026-03-06T23:05:02Z")
Greetings everyone, I intend to calculate the time dependent correlation function with TDVP algorithm. I applied the 2-site TDVP. The result is a bit strange, since the correlation function is oscillating (negative and… --- ## [Problem with exp and sparse matrices](https://itensor.discourse.group/t/problem-with-exp-and-sparse-matrices/2589)
**Author:** [@Joacop16](https://itensor.discourse.group/u/Joacop16)\ **Replies:** 1\ **Last updated:** [March 2, 2026, 9:05pm UTC](https://itensor.discourse.group/t/problem-with-exp-and-sparse-matrices/2589 "2026-03-02T21:05:18Z")
Hi, For a research project of spinful fermions I need to implement TEBD, I wanted to do it with symmetries because my Hamiltonian conserves the total number of particles (not by spin but it respects the total number). H… --- ## [Fermionic hopping dressed with quantized Peierls phase and conservation of fermions](https://itensor.discourse.group/t/fermionic-hopping-dressed-with-quantized-peierls-phase-and-conservation-of-fermions/2574)
**Author:** [@FerdinandToelkes](https://itensor.discourse.group/u/FerdinandToelkes)\ **Replies:** 1\ **Last updated:** [February 23, 2026, 8:15am UTC](https://itensor.discourse.group/t/fermionic-hopping-dressed-with-quantized-peierls-phase-and-conservation-of-fermions/2574 "2026-02-23T08:15:51Z")
Hello again, I am working on the one dimensional extended Hubbard model for spinless fermions and a light matter coupling that is introduced via the quantized Peierls phase. I want to implement this for open and periodi… [Next page](https://itensor.discourse.group/latest.md?page=1)