QEncode Benchmark
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C4H6

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

C4H6_ccpvdz_JW_ADAPT_v4_tapered__sha256_d70625e50afebe76

VQE Gap

2.8286e-3 Ha

CASCI ref

-154.921897 Ha

Qubits (tapered)

4

CCSD(T) corr.

-6.258e-1 Ha

Molecule / Problem

NameC4H6
Basis setcc-pvdz
GeometryC 0.0 0.0 0.6695; C 0.0 0.0 -0.6695; C 0.0 1.2288 1.3978; C 0.0 -1.2288 -1.3978; H 0.0 2.1501 0.8386; H 0.0 1.2396 2.4742; H 0.0 -2.1501 -0.8386; H 0.0 -1.2396 -2.4742; H 0.0 0.9217 -1.2788; H 0.0 -0.9217 1.2788
Charge0
Spin0
Active electrons4
Active orbitals4
Orbital optimizationHF

Encoding / Circuit

Qubit mappingjordan-wigner
Ansatz typeadapt
Ansatz reps (HEA)1
TaperingZ2 symmetry — 4 symmetries removed
Qubits (original)8
Qubits (tapered)4
Num parameters1
Circuit depth20
2Q gates14
Non-Clifford gates8
T gates (FT estimate)96 (ε = 0.001)

T-gate count is the resource-relevant cost of a fault-tolerant implementation. It is an estimate from the non-Clifford rotations in the pre-transpilation circuit, assuming standard rotation synthesis to precision ε — not a compiled count for a specific device.

Energy Results

HF energy-154.8993843213 Ha
MP2 energy-155.4569210310 Ha
CCSD energy-155.5000626191 Ha
CCSD(T) energy-155.5252019040 Ha
CASCI ground state-154.9218973816 Ha
VQE best energy-154.9190688030 Ha
|VQE − CASCI| gap2.828579e-3 Ha
CCSD(T) correlation-6.258176e-1 Ha

Optimizer / Run Config

AlgorithmADAPT-VQE (COBYLA inner)
Multistart runs1
Max iterations500
Total func evals21
Num parameters1
Backenddefault.qubit

Provenance / Reproducibility

Entry IDC4H6_ccpvdz_JW_ADAPT_v4_tapered__sha256_d70625e50afebe76
Schema version4.0.0
Created (UTC)2026-07-16T09:36:26.872827+00:00
SHA-256 hashd70625e50afebe765148ad8dff340d4b96ae89854d9a892f61c7fffe3155a828
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 C4H6 \

--mapping jordan_wigner \

--ansatz-type adapt \

--reps 1 \

--multistart 1 \

--max-iter 500 \

--out-dir releases/v4/db

View raw JSON on GitHub