hermi 0.1.0

The hermi package implements integrals over atom-centred Gaussian basis functions for use in quantum chemistry. It implements a generalised McMurchie--Davidson algorithm which targets matrix operations in order to effectively vectorise the workload via NumPy calls. This permits efficient integral generation without any custom compiled code.

Installation

The package can be installed from the PyPI repository:

pip install hermi

Alternatively, clone the repository and install via the source code:

git clone https://github.com/obackhouse/hermi.git
cd hermi && pip install .

Usage

Helper classes for molecules and basis sets are implemented:

from hermi import Molecule, Basis
molecule = Molecule.from_list(["Li", "H"], [[0.0, 0.0, 0.0], [0.0, 0.0, 1.64]])
basis = Basis.from_molecule(molecule, "6-31g")

The automatic basis construction uses the basis-set-exchange library. Operators can then be constructed and evaluated over the basis set:

from hermi import Overlap
overlap = Overlap()
matrix = overlap.collect(basis)

Operators are also composable; along with lazy evaluation and caching, this can afford optimisations when computing molecular integrals summed over a number of operators:

from hermi import Kinetic, Nuclear
core_hamiltonian = Kinetic() + Nuclear(molecule)
matrix = core_hamiltonian.collect(basis)

Development

We recommend uv for development, install development dependencies and run the test suite with:

uv sync --extra dev
uv run pytest

The operator integration tests compare Cartesian and spherical integrals against PySCF.

References

This work is based on several papers: first, the original paper of McMurchie and Davidson, and more specifically, the modern implementations detailed in papers by Neese and by Asadchev and Valeev.