ferric

A Rust-native quantum chemistry engine, wrapping libint2 for electron integrals, with pyo3 Python bindings.

ferric is organized around one object: electronic response — how the density reacts to a perturbation. That object shows up as the polarizability \( \alpha \), the dielectric function \( \varepsilon \), and the susceptibility \( \chi \), and the methods here are three faces of getting it right where standard methods get it wrong.

• Attenuated MP2 — MP2 builds dispersion from an uncoupled polarizability that over-polarizes, giving too-large \( C_6 \) and overestimated π-stacking. Attenuating the correlation operator tames that response error with a single tunable parameter.
• PDEP-RPA / GW — the dielectric matrix is the density–density response. PDEP keeps only its dominant low-rank eigenmodes, so RPA correlation and the GW screened interaction need no explicit sum over empty states.
• Constrained DFT — a constraint couples to the density and reads its response (\( \partial N / \partial \lambda \) is a susceptibility), building charge-localized diabatic states and their electron-transfer couplings.

The motivating claim is that response is local in real space and low-rank in its eigenspectrum, so organizing around it should make the computation cheaper.

Implemented ≠ validated

Working code is not a checked number. This documentation describes what exists; it is not a claim that every number is trustworthy.

For how strongly each capability's numbers are checked against ground truth — and where they are known to fail — see What is validated. Capability maturity varies a great deal between methods, and they are graded individually rather than presented as a flat list of equals.

Where to start

Source

github.com/mgoldey/ferric — dual-licensed MIT / Apache-2.0.