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H4

/jordan wigner/uccsd tapered
Certified
Beats CCSD(T)
cc-pvdz

H4_ccpvdz_JW_UCCSD_v4_tapered__sha256_7606caf47ff39f40

VQE Gap

2.2218e-3 Ha

CASCI ref

-2.186232 Ha

Qubits (tapered)

5

CCSD(T) corr.

-8.731e-2 Ha

Molecule / Problem

NameH4
Basis setcc-pvdz
GeometryH 0.0 0.0 0.0; H 0.0 0.0 1.0; H 0.0 0.0 2.0; H 0.0 0.0 3.0
Charge0
Spin0
Active electrons4
Active orbitals4
Orbital optimizationHF

Encoding / Circuit

Qubit mappingjordan-wigner
Ansatz typeuccsd_tapered
Ansatz reps (HEA)1
TaperingZ2 symmetry — 3 symmetries removed
Qubits (original)8
Qubits (tapered)5
Num parameters64
Circuit depth120
2Q gates24

Note on UCCSD circuit metrics

UCCSD uses exponential Pauli operators (exp(iθH)) that are symbolic before compilation. Circuit depth and 2-qubit gate counts are not reported here — they depend on the target hardware and transpiler.

Energy Results

HF energy-2.1664914658 Ha
MP2 energy-2.2312373418 Ha
CCSD energy-2.2529496914 Ha
CCSD(T) energy-2.2538030394 Ha
CASCI ground state-2.1862316746 Ha
VQE best energy-2.1840098797 Ha
|VQE − CASCI| gap2.221795e-3 Ha
CCSD(T) correlation-8.731157e-2 Ha

Optimizer / Run Config

AlgorithmCOBYLA
Multistart runs1
Max iterations1000
Total func evals1,000
Num parameters64
Backenddefault.qubit

Provenance / Reproducibility

Entry IDH4_ccpvdz_JW_UCCSD_v4_tapered__sha256_7606caf47ff39f40
Schema version4.0.0
Created (UTC)2026-07-15T13:22:17.854426+00:00
SHA-256 hash7606caf47ff39f409699573ea0bbc06548a70c765c748889c0d9dae99092909c
Python3.11.15
PySCF2.6.2
PennyLane0.45.0
OpenFermion1.6.1
NumPy2.2.6
SciPy1.13.1

Reproduce this result

# Clone repo and install pinned environment

git clone https://github.com/qencode-benchmark/qencode-benchmark

cd qencode-benchmark

pip install -r requirements-v4.txt

# Run this entry

python scripts/generate_entry_v4.py \

--molecule H4 \

--mapping jordan_wigner \

--ansatz-type uccsd \

--multistart 1 \

--max-iter 1000 \

--out-dir releases/v4/db

View raw JSON on GitHub