QEncode Benchmark
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C4H4

/parity/hea
Certified
Beats CCSD(T)
cc-pvdz
CASSCF

C4H4_ccpvdz_PAR_HEA_v4_casscf_tapered__sha256_8b12a22329451c03

VQE Gap

3.8341e-3 Ha

CASCI ref

-153.673427 Ha

Qubits (tapered)

5

CCSD(T) corr.

-5.957e-1 Ha

Molecule / Problem

NameC4H4
Basis setcc-pvdz
GeometryC 0.673 0.783 0.0; C -0.673 0.783 0.0; C -0.673 -0.783 0.0; C 0.673 -0.783 0.0; H 1.377 1.602 0.0; H -1.377 1.602 0.0; H -1.377 -1.602 0.0; H 1.377 -1.602 0.0
Charge0
Spin0
Active electrons4
Active orbitals4
Orbital optimizationCASSCF

Encoding / Circuit

Qubit mappingparity
Ansatz typehea
Ansatz reps (HEA)2
TaperingZ2 symmetry — 3 symmetries removed
Qubits (original)8
Qubits (tapered)5
Num parameters15
Circuit depth10
2Q gates8
Non-Clifford gates15
T gates (FT estimate)180 (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-153.6528244194 Ha
MP2 energy-154.1870717643 Ha
CCSD energy-154.2235763592 Ha
CCSD(T) energy-154.2485698632 Ha
CASSCF energy-153.6734265501 Ha
CASCI ground state-153.6734265501 Ha
VQE best energy-153.6695924228 Ha
|VQE − CASCI| gap3.834127e-3 Ha
CCSD(T) correlation-5.957454e-1 Ha

Optimizer / Run Config

AlgorithmCOBYLA
Multistart runs3
Max iterations500
Total func evals1,500
Num parameters15
Backenddefault.qubit

Provenance / Reproducibility

Entry IDC4H4_ccpvdz_PAR_HEA_v4_casscf_tapered__sha256_8b12a22329451c03
Schema version4.0.0
Created (UTC)2026-09-07T12:11:55.428809+00:00
SHA-256 hash8b12a22329451c03e47f09e6bb05d824d1c5507a9238ca8b9e116a2d04c2fc00
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 C4H4 \

--mapping parity \

--ansatz-type hea \

--reps 2 \

--orbital-opt casscf \

--multistart 3 \

--max-iter 500 \

--out-dir releases/v4/db

View raw JSON on GitHub