wickd 1.2.2

An example minimal project that compiles bindings using nanobind and scikit-build

Wick&d

Wick&d is a Python library for the algebra of second quantization for fermionic systems. It implements Wick's contraction theorem for general Fermi vacua, making it well-suited for deriving equations in quantum chemistry methods such as coupled cluster, MBPT, and multireference theories.

Quick start

# Define a Slater determinant reference with occupied (o) and virtual (v) spaces
w.reset_space()
w.add_space("o", "fermion", "occupied", ["i", "j", "k", "l"])
w.add_space("v", "fermion", "unoccupied", ["a", "b", "c", "d"])

# Build the operators F
F = w.utils.gen_op("f", 1, "ov", "ov")
# Build the one-body operator T1 (occupied to virtual)
T1 = w.op("t", ["v+ o"])

# Build the product of F and T1
F_T1 = F @ T1

# Apply Wick's theorem and collect all fully contracted terms
wt = w.WickTheorem()
expr = wt.contract(F_T1, minrank=0, maxrank=4)

print(f"F T_{{1}} = {expr.latex()}")

Installation

From PyPI:

pip install wickd

Development version:

git clone https://github.com/fevangelista/wickd.git
cd wickd
pip install nanobind scikit-build-core[pyproject]
pip install --no-build-isolation -ve .

Requirements

• Python ≥ 3.9
• macOS or Linux
• Boost (optional) — enables 1024-bit integer arithmetic for large prefactors; the library builds and runs without it

Testing

pip install pytest
pytest

Learning resources

• Jupyter tutorials — step-by-step introduction to the library
• Examples — worked derivations (e.g. coupled cluster equations)

Citation

If you use Wick&d in your research, please cite:

@article{Evangelista2022,
  author  = {Evangelista, Francesco A.},
  title   = {Automatic derivation of many-body theories based on general {Fermi} vacua},
  journal = {J. Chem. Phys.},
  volume  = {157},
  pages   = {064111},
  year    = {2022},
  doi     = {10.1063/5.0097858},
  url     = {https://doi.org/10.1063/5.0097858},
}

Contributing

Bug reports and pull requests are welcome via GitHub Issues.

License

Wick&d is released under the MIT License.