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All instances / Heisenberg

Heisenberg square 6x6

Exact energy and best values (rules §6)

exact -0.6788721 ED
Richter et al. (2004) · the instance is solved
best variational -0.678871(3) VMC (CNN BF + RBM)
Hendry et al. (2025) · the lowest unflagged variational energy, a strict variational bound
best extrapolated -0.67887177(7) VMC (2D RNN)
Moss et al. (2025) · the lowest unflagged extrapolated energy, an extrapolation, not a bound

Energies as E/N (S.S). Classes are different claims and are not ranked against each other.

The Hamiltonian

H = ∑⟨ij⟩ σi·σj

Nearest-neighbour Heisenberg antiferromagnet, J = 1, written with Pauli matrices.

lattice
square
sites
36
boundary
periodic
energies
14

Stored as a total energy; quoted here as E/N (S.S), which is what the papers report (how the conversion works).

Every published energy

Grouped by what the number is. The exact energy comes first where there is one; in every other group the lowest unflagged energy is its best value, and each row's distance is to that best (rules §6).

Numerically exact (3)

Exact diagonalization, an exact solution, or sign-problem-free QMC where that is established. An exact energy is shown first, before the best of each other class. QMC is exact only within its error bar, which it must state, and reads exact (stochastic); an exact diagonalization outranks it. For a diagonalization resolved by symmetry sector only the ground state's sector is listed; the lowest energies of the other sectors are the instance's spectrum, in its JSON, and are not shown as the exact energy.

E/N (S.S)distance to class bestσVar(E)V-score methodsourcecodeyearcomment
-0.67887215 −<1e-7 2.0e-8 n/a n/a SSE QMC
peer reviewed
Sandvik (2026) 2026
-0.6788721 0 n/a n/a n/a ED
VarBench reference run
Wu et al. (2024) run script 2024
-0.6788721exact 0 n/a n/a n/a ED
book chapter
Richter et al. (2004) 2004

Strict variational upper bounds (10)

Energies that a variational state reached (VMC, DMRG and MPS at finite bond dimension, PEPS, NQS, VQE). Each is an upper bound on the ground-state energy.

E/N (S.S)distance to class bestσVar(E)V-score methodsourcecodeyearcomment
-0.678871best variational 0 3.0e-6 n/a n/a VMC (CNN BF + RBM)
peer reviewed
Hendry et al. (2025) uses NetKet 2025
-0.67887tied with best variational at 2σ 1.0e-6 2.0e-5 6.11e-2 2.3e-4 VMC (2D RNN)
peer reviewed
Moss et al. (2025) mschuylermoss/HeisenbergRNN 2025
-0.67887tied with best variational at 2σ 1.0e-6 n/a n/a n/a VMC (ViT)
preprint
Golubev et al. (2026) uses NetKet 2026
-0.678868tied with best variational at 2σ 3.0e-6 2.0e-6 n/a n/a VMC (RBM)
peer reviewed
Chen et al. (2022) 2022
-0.67882 5.1e-5 1.0e-5 n/a n/a VMC (CNN)
peer reviewed
Choo et al. (2019) uses NetKet 2019
-0.6788 7.1e-5 n/a n/a n/a VMC (CNN)
peer reviewed
Ou et al. (2025) 2025
-0.6786224 2.5e-4 n/a 1.39e+0 5.2e-3 DMRG
VarBench reference run
Wu et al. (2024) run script 2024
-0.6785tied with best variational at 2σ 3.7e-4 2.0e-4 n/a n/a VMC (EPS)
peer reviewed
Mezzacapo et al. (2009) 2009
-0.66974 9.1e-3 2.6e-5 1.47e+1 5.7e-2 VMC (Jastrow)
VarBench reference run
Wu et al. (2024) run script 2024
-0.66854 1.0e-2 2.6e-5 1.39e+1 5.4e-2 VMC (RBM)
VarBench reference run
Wu et al. (2024) run script 2024

Extrapolations (1)

Zero-variance or bond-dimension extrapolations. These are not bounds: no ansatz reached the number.

E/N (S.S)distance to class bestσVar(E)V-score methodsourcecodeyearcomment
-0.67887177best extrapolated 0 7.0e-8 n/a n/a VMC (2D RNN)
peer reviewed
Moss et al. (2025) mschuylermoss/HeisenbergRNN 2025

How these numbers were read

Where each number below was read, and how it was checked.

-0.67887215(2), SSE QMC

Checked 2026-09-15 · arXiv HTML parsed locally, one value per table cell; no LLM transcription

Reported as. e0 = -0.67887215(2) per spin (S.S), L = 6, periodic

Table 1, "Results for different system sizes computed at inverse temperature beta/L = 64 for L > 30 and averaged over beta/L = 32 and beta/L = 64 simulations for L <= 30", column e0, row L = 6. Pauli total = 4 N e0. The L = 6 value agrees with the exact-diagonalization row on square_36_P to 1.6e-8.

-0.6788721, ED

Checked 2026-09-29 · prior recomputation: E2 ed_sym.py (numba, table-based symmetric basis), output qmbl-runs/qmbl-verify/out/E2-exact-remote/results/sym36/Heisenberg__square_36_P__J2_0__k0-0__c4v-irrep0__z+.json (evidence cited by the plan: qmbl-verify/out/E2-exact-remote (verified))

Reported as. -97.75758959723629 (true residual ||Hx-Ex||/||x|| = 6.19e-11); S^z=0, k=0, C4v A1, spin inversion +1

Real recomputation (code and output file). |E - stored| = 5.97e-13 (relative 6.11e-15). Second determination: the stored value is the source's own ED (VarBench), a different code. Also read by VB3-varbench-code-heisenberg#50 (scope config: vendor/varbench/Heisenberg/square_36_P.md (snapshot 390a21e), row 'Exact diagonalization'; linked scripts/Heisenberg/square_36_P/ed_lattice_symmetries.sh).

-0.6788721, ED

Checked 2026-10-24 · arXiv:cond-mat/0412662: publisher PDF (Springer, scanned) Table 2.1, read from the page image rendered at 200 %; checked against the arXiv text (pypdf layout and plain modes); no LLM transcription of numbers; single reading + page-image check

Reported as. −24.4393974

Table 2.1 (p. 102), row N = 36, edge vectors (6, 0), (0, 6), column E0. The caption says the N = 36 results agree with Schulz et al. [55]; the stored ED energy -97.7575895972 is this value to its printed digits. | Spin-1/2 Heisenberg antiferromagnet H = J sum_<ij> S_i . S_j on the square lattice, J = 1, periodic boundaries on the finite lattice defined by the two edge vectors printed in the row (Betts construction, Sec. 2.4.1); E0 is the total singlet ground-state energy in S.S units, stored as the Pauli total 4 E0. Version read: publisher PDF (Springer, a scan), Table 2.1 on p. 102 read from the page image; identical to Table 1 of the arXiv text cond-mat/0412662. Peer review: a chapter of an edited lecture-notes volume, not a refereed journal.

-0.67887177(7), VMC (2D RNN)

Checked 2026-09-14 · arXiv HTML parsed locally from a benchmark comparison table, no LLM transcription

Reported as. -0.67887177 (+/- 7e-8) per site in S.S units

Read from Table 5 of arXiv:2502.17144 (SLAHM, E/N in S.S units), parsed from the arXiv HTML. Row "This work (zero-variance)". The paper states in the Table 3 caption that these extrapolated values can fall below the reference energies and that this is "an artifact of the zero-variance extrapolation" - not an achieved energy, so NOT a bound (RULES.md 4).

-0.678871(3), VMC (CNN BF + RBM)

Checked 2026-09-15 · source text of arXiv:2507.10287 read locally (arXiv HTML or pypdf layout text); value copied from the harvested cell and the text, no LLM transcription of numbers; adversarial re-read: confirmed

Reported as. -0.678871(3)

Table I, row (qx,qy,qsf)=(0,0,0), column |E0>, data row 'E/Ns': -0.678871(3) (source text lines 1012-1013). This is the global minimum across all 16 momentum/spin-flip sectors and all 4 excited states listed in Table I, confirming it is the true ground state (Gamma-point sector). | Own ED value on the same row (EED/Ns=-0.67887215) matches instance exact_per_site=-0.6788721499808035 to 8 decimals, fixing per-site S.S convention with no rescaling; 'square lattice geometries with periodic boundary conditions along both spatial directions' (Sec. V) plus the use of momentum labels (qx,qy) fixes this as the periodic (_P), not open (_O), 36-site instance.

-0.67887(2), VMC (2D RNN)

Checked 2026-09-14 · arXiv HTML parsed locally from a benchmark comparison table, no LLM transcription

Reported as. -0.67887 (+/- 0.00002) per site in S.S units

Read from Table 5 of arXiv:2502.17144 (SLAHM, E/N in S.S units), parsed from the arXiv HTML. Row "This work (best RNN)".

-0.67887, VMC (ViT)

Checked 2026-09-15 · source text of arXiv:2606.04558 read locally (arXiv HTML or pypdf layout text); value copied from the harvested cell and the text, no LLM transcription of numbers; single reading

Reported as. -0.678870

Table I, row J2=0.00, column '6×6, ViT (this work)' | Table I value is already printed per-site (not total): e.g. 6×6 ED at J2=0.50 prints -0.503809, exactly matching catalog J1J2/square_36_P_0.5 exact_per_site -0.5038096539; the J2=0.00 quoted QMC column value -0.67349005 [29] exactly equals catalog Heisenberg/square_64_P exact_per_site -0.67349005 (and -0.67155266 [29] equals Heisenberg/square_100_P exact_per_site -0.67155266) — confirms direct S·S per-site match, no Pauli conversion needed.

-0.678868(2), VMC (RBM)

Checked 2026-09-14 · found in the citing paper's comparison table, then confirmed in the primary source's own PDF (pypdf); no LLM transcription

Reported as. -0.678868 (+/- 0.000002) per site in S.S units

Read from Table 5 of arXiv:2502.17144 (SLAHM, E/N in S.S units), parsed from the arXiv HTML. Row "RBM+Lanczos [40]" = arXiv:2206.14307. CONFIRMED IN PRIMARY SOURCE - arXiv:2206.14307 Table 4: "6x6 -0.678873(4) 2.51799(6) -0.678868(2) 2.51(2)" - Energy(QMC) beside Energy(RBM).

-0.67882(1), VMC (CNN)

Checked 2026-09-14 · arXiv HTML parsed locally from a benchmark comparison table, no LLM transcription

Reported as. -0.67882 (+/- 0.00001) per site in S.S units

Read from Table 5 of arXiv:2502.17144 (SLAHM, E/N in S.S units), parsed from the arXiv HTML. Row "CNN [33]" = Phys. Rev. B 100, 125124 (2019).

-0.6788, VMC (CNN)

Checked 2026-09-15 · source text of arXiv:2510.02051 read locally (arXiv HTML or pypdf layout text); value copied from the harvested cell and the text, no LLM transcription of numbers; single reading

Reported as. -0.6788

S5.p7: 'At J2/J1=0, our work yields -0.6788, showing excellent agreement with the exact value [59] of -0.678872' | 6x6=36-site periodic square lattice, J2=0 reduces J1-J2 model to plain Heisenberg; matches catalogue Heisenberg/square_36_P by exact-value agreement.

-0.6786224, DMRG

Checked 2026-09-29 · VarBench snapshot 390a21e (vendor/varbench) and full upstream history (varbench-history, git log --follow on the file, every version); varbench/methods ed31bb0 run script and program read as text; no output log or result file exists in the methods repo for any Heisenberg row

Reported as. | -97.72162414290578 | | 1.385137434483113 | 36 | 0 | DMRG (bond dimension = 2048) | [code](https://github.com/varbench/methods/blob/main/scripts/Heisenberg/square_36_P/dmrg.sh) |

dmrg.sh: heisenberg_2d.jl --peri --L 6 --zero_mag --max_B 2048: 6x6 torus, Pauli, J = 1, Sz = 0, 50 sweeps at D = 2048. 0.0360 above the exact energy (a torus in a snake MPS); var/(E - E0) = 38.5. Entered 721e09e (2022-08-22), never changed; linked 2024-07-19.

-0.6785(2), VMC (EPS)

Checked 2026-09-15 · source text of arXiv:2510.02051 read locally (arXiv HTML or pypdf layout text); value copied from the harvested cell and the text, no LLM transcription of numbers; single reading

Reported as. -0.6785(2)

S5.p7: 'VMC method [60] gives -0.6785(2)' | Same 36-site periodic Heisenberg instance.

-0.66974(3), VMC (Jastrow)

Checked 2026-09-29 · VarBench snapshot 390a21e (vendor/varbench) and full upstream history (varbench-history, git log --follow on the file, every version); varbench/methods ed31bb0 run script and program read as text; no output log or result file exists in the methods repo for any Heisenberg row

Reported as. | -96.4427 | 0.0038 | 14.7488 | 36 | 0 | Jastrow baseline | [code](https://github.com/varbench/methods/blob/main/scripts/Heisenberg/square_36_P/vmc_jastrow.sh) |

scripts/Heisenberg/square_36_P/vmc_jastrow.sh: 'python3 vmc.py --ham heis --boundary peri --sign mars --ham_dim 2 --L 6 --zero_mag --net jas --seed 123 --show_progress' -> 6x6 square lattice, periodic (nk.graph.Grid); NetKet Heisenberg J = 1 in Pauli form with Marshall sign rule (a sublattice rotation on a bipartite lattice, spectrum unchanged); Sz = 0 (total_sz=0, MetropolisExchange); real float32 Jastrow (nk.models.Jastrow); 10^4 SR steps; final estimate over 2^20 samples (vmc.py lines 268-269). sigma/sqrt(Var/2^20) = 1.013: the stored sigma is the error of that final estimate. 1.3149 above the exact -97.7575895972357. History: entered af1d48f (2022-09-01, Dian Wu) as -96.4427 | 0.0038 | 14.7488 | Jastrow baseline; linked fdb4bfb (2024-07-30). Program files postdate the value (scripts added to varbench/methods 2024-07-30); they document the settings after the run.

-0.66854(3), VMC (RBM)

Checked 2026-09-29 · VarBench snapshot 390a21e (vendor/varbench) and full upstream history (varbench-history, git log --follow on the file, every version); varbench/methods ed31bb0 run script and program read as text; no output log or result file exists in the methods repo for any Heisenberg row

Reported as. | -96.2702 | 0.0037 | 13.9167 | 36 | 0 | RBM (alpha = 1) | [code](https://github.com/varbench/methods/blob/main/scripts/Heisenberg/square_36_P/vmc_rbm.sh) |

scripts/Heisenberg/square_36_P/vmc_rbm.sh: 'python3 vmc.py --ham heis --boundary peri --sign mars --ham_dim 2 --L 6 --zero_mag --net rbm --seed 123 --show_progress' -> 6x6 square lattice, periodic (nk.graph.Grid); NetKet Heisenberg J = 1 in Pauli form with Marshall sign rule (a sublattice rotation on a bipartite lattice, spectrum unchanged); Sz = 0 (total_sz=0, MetropolisExchange); real float32 RBM, alpha = 1 (nk.models.RBM, log_cosh); 10^4 SR steps; final estimate over 2^20 samples (vmc.py lines 268-269). sigma/sqrt(Var/2^20) = 1.016: the stored sigma is the error of that final estimate. 1.4874 above the exact -97.7575895972357. History: entered 721e09e (2022-08-22, Dian Wu) as -96.2702 | 0.0037 | 13.9167 | RBM (alpha = 1); linked 5047bfd (2024-07-30). Program files postdate the value (scripts added to varbench/methods 2024-07-30); they document the settings after the run.

Coverage

Newest published number here: 2026. Literature last checked 2026-09-15 (table harvest of cached arXiv sources (match_tables.mjs --all), every matched paper read for this instance): 13 papers read, 3 of them with an energy on this page.

This instance as data

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