PyQInt: A Teaching-Oriented Hartree–Fock Implementation in Python

PyQInt is a modular Python package for learning and prototyping quantum chemistry methods, with a particular focus on the Hartree-Fock formalism (Roothaan, 1951) using
Gaussian-type orbitals (Pople et al., 1995). Designed to prioritize educational transparency, PyQInt exposes all computational building blocks—integrals, matrices, Hamiltonians, SCF procedures, and gradients—through a clean, inspectable API.
Users can evaluate molecular integrals (Taketa et al., 1966), perform self-consistent field calculations with direct inversion of iterative subspace (DIIS) (Pulay, 1980), construct
and localize orbitals, compute crystal orbital Hamilton population (COHP) coefficients (Dronskowski & Bloechl, 1993), and optimize molecular geometries. PyQInt is especially
well suited for students and researchers who want to interact with and understand the underlying steps of electronic structure theory, offering full access to intermediate data
structures and algorithmic pathways.
While numerical efficiency is not the primary goal, PyQInt connects to a C++ backend for integral evaluation, enabling practical computations on small molecules. The package is fully documented and tested, and is ideal for use in courses, tutorials, or prototyping new electronic structure ideas.