QEncode Benchmark
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H2O

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

H2O_ccpvdz_JW_UCCSD_v4_tapered__sha256_1a15dd08a75640a5

VQE Gap

1.4370e-7 Ha

CASCI ref

-76.027338 Ha

Qubits (tapered)

4

CCSD(T) corr.

-2.163e-1 Ha

Molecule / Problem

NameH2O
Basis setcc-pvdz
GeometryO 0.0 0.0 0.0; H 0.0 0.757 0.586; H 0.0 -0.757 0.586
Charge0
Spin0
Active electrons4
Active orbitals4
Orbital optimizationHF

Encoding / Circuit

Qubit mappingjordan-wigner
Ansatz typeuccsd_tapered
Ansatz reps (HEA)1
TaperingZ2 symmetry — 4 symmetries removed
Qubits (original)8
Qubits (tapered)4
Num parameters18
Circuit depth34
2Q gates12

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-76.0267936450 Ha
MP2 energy-76.2307620086 Ha
CCSD energy-76.2400859051 Ha
CCSD(T) energy-76.2431421376 Ha
CASCI ground state-76.0273383586 Ha
VQE best energy-76.0273382149 Ha
|VQE − CASCI| gap1.437017e-7 Ha
CCSD(T) correlation-2.163485e-1 Ha

Optimizer / Run Config

AlgorithmCOBYLA
Multistart runs1
Max iterations500
Total func evals279
Num parameters18
Backenddefault.qubit

Provenance / Reproducibility

Entry IDH2O_ccpvdz_JW_UCCSD_v4_tapered__sha256_1a15dd08a75640a5
Schema version4.0.0
Created (UTC)2026-07-15T13:20:55.884833+00:00
SHA-256 hash1a15dd08a75640a5552335f057b0e00fc56e16918bd035b164071df056ab2050
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 H2O \

--mapping jordan_wigner \

--ansatz-type uccsd \

--multistart 1 \

--max-iter 500 \

--out-dir releases/v4/db

View raw JSON on GitHub