openfermion

library1.7.1pypypi✓ verified 84d ago

OpenFermion is an open-source library for quantum chemistry simulation on quantum computers. Version 1.7.1 (requires Python >=3.10) provides tools for mapping fermionic Hamiltonians to qubit operators, variational quantum eigensolver (VQE) workflows, and interfaces to quantum computing SDKs. Released periodically, approximately quarterly.

ai-ml data workflow

pip install openfermion

package ↗homepage ↗

INSTALL

IMPORT

SIG · OPENFERMION

openfermion

ai-mlpythonv1.7.1

Install

24.8s avg

Import

8587ms

Disk

602MB

Pass rate

9/ 10

Env Coverage9 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v1.7.1 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

glibc

py 3.10

✓ —

✓ 23.7s

py 3.11

✓ —

✓ 23.4s

py 3.12

✓ —

✓ 24.5s

py 3.13

✓ —

✓ 24.9s

py 3.9

✕ build_error

✓ 27.5s

602MB installed

● package 602MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

get_sparse_operator

✓ from openfermion import get_sparse_operator

✗ from openfermion.ops import get_sparse_operator

Deprecated path; function is now at top-level

qubit_operator_sparse

✓ from openfermion import qubit_operator_sparse

✗ from openfermion.utils import qubit_operator_sparse

Moved to top-level in v1.0+

MolecularData

✓ from openfermion import MolecularData

✗ from openfermion.hamiltonians import MolecularData

Deprecated submodule; use top-level import

Basic workflow: load molecular data, obtain fermionic Hamiltonian, map to qubit operator, and inspect sparse matrix representation.

import openfermion as of # Create a simple hydrogen molecule (minimal basis) geometry = [('H', (0.0, 0.0, 0.0)), ('H', (0.0, 0.0, 0.7414))] molecule = of.MolecularData(geometry, basis='sto-3g', multiplicity=1, charge=0) molecule.load() # Get the fermionic Hamiltonian hamiltonian = molecule.get_molecular_hamiltonian() print(hamiltonian) # Map to qubit Hamiltonian (Jordan-Wigner) qubit_ham = of.jordan_wigner(hamiltonian) print(qubit_ham) # Get sparse matrix sparse_mat = of.get_sparse_operator(qubit_ham) print(sparse_mat.shape)

Debug

Known issues

breakingIn v1.0, many top-level imports changed from submodules (e.g., `openfermion.ops`, `openfermion.utils`) to direct `openfermion`. Code using old import paths will break.

fix

Replace e.g. `from openfermion.ops import InteractionOperator` with `from openfermion import InteractionOperator`.

affects: >=1.0.0

deprecated`get_ground_state` function is deprecated. Use `eigensolver` from `openfermion` or `scipy.sparse.linalg.eigsh`.

fix

Use `from openfermion import eigensolver` or `scipy.sparse.linalg.eigsh`.

affects: >=1.5.0

gotchaWhen using `MolecularData`, the molecule must be loaded with `.load()` before accessing properties. Forgetting this raises an `AttributeError`.

fix

Always call `molecule.load()` after creating `MolecularData` object.

affects: all

gotchaThe Jordan-Wigner transform of a large Hamiltonian can produce a very dense operator; consider using Bravyi-Kitaev or other transforms for efficiency.

fix

Use `of.bravyi_kitaev(hamiltonian)` or `of.symmetric_jordan_wigner(hamiltonian)` to reduce qubit count or operator weight.

affects: all

Errors

Common errors & fixes

AttributeError: 'MolecularData' object has no attribute 'n_qubits'

MolecularData was not loaded. Accessing attributes before `.load()` fails.

fix

Add `molecule.load()` after constructing the MolecularData object.

ImportError: cannot import name 'InteractionOperator' from 'openfermion'

In versions >=1.0, the import path changed. InteractionOperator is still available but must be imported from `openfermion.ops` only in older versions.

fix

Use `from openfermion import InteractionOperator` (v1.0+) or `from openfermion.ops import InteractionOperator` (v0.x). Check your version.

ModuleNotFoundError: No module named 'openfermionpyscf'

openfermionpyscf is a separate plugin package for PySCF integration. Not included by default.

fix

Install with `pip install openfermionpyscf` and import as `import openfermionpyscf`.

Upgrade

Version history

1.7.1latest on PyPI · released Jun 6, 2025

Audit

Dependencies

cirqoptionalUsed for quantum circuit simulation and interfaces

pyscfoptionalProvides molecular data and integrals

numpyrequiredNumerical computing backbone

Agent activity

29 hits · last 30 days

node

Amazon

OpenAI (training)

Resources

packagehttps://pypi.org/project/openfermion/ ↗

homepagehttps://quantumai.google/openfermion ↗