QEncode Benchmark
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water_dimer

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

water_dimer_ccpvdz_PAR_HEA_v4_tapered__sha256_f69363eea8e031ae

VQE Gap

1.1417e-4 Ha

CASCI ref

-152.062719 Ha

Qubits (tapered)

5

CCSD(T) corr.

-4.352e-1 Ha

Molecule / Problem

Namewater_dimer
Basis setcc-pvdz
GeometryO -1.551007 -0.114520 0.000000; H -1.934259 0.762503 0.000000; H -0.599677 0.040712 0.000000; O 1.350625 0.111469 0.000000; H 1.680398 -0.373741 -0.758561; H 1.680398 -0.373741 0.758561
Charge0
Spin0
Active electrons4
Active orbitals4
Orbital optimizationHF

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-152.0625362496 Ha
MP2 energy-152.4734315200 Ha
CCSD energy-152.4912439611 Ha
CCSD(T) energy-152.4977225163 Ha
CASCI ground state-152.0627193590 Ha
VQE best energy-152.0626051904 Ha
|VQE − CASCI| gap1.141685e-4 Ha
CCSD(T) correlation-4.351863e-1 Ha

Optimizer / Run Config

AlgorithmCOBYLA
Multistart runs1
Max iterations500
Total func evals500
Num parameters15
Backenddefault.qubit

Provenance / Reproducibility

Entry IDwater_dimer_ccpvdz_PAR_HEA_v4_tapered__sha256_f69363eea8e031ae
Schema version4.0.0
Created (UTC)2026-09-07T12:12:13.712852+00:00
SHA-256 hashf69363eea8e031ae304f45204f1e172345b343f4483a4919431cf17ac43ba685
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 water_dimer \

--mapping parity \

--ansatz-type hea \

--reps 2 \

--multistart 1 \

--max-iter 500 \

--out-dir releases/v4/db

View raw JSON on GitHub