ferric

A quantum chemistry engine written in Rust, with Python bindings and a TOML-driven command line. libint2 supplies the integrals and libxc the functionals.

Documentation: https://matthew.thegoldeys.com/ferric/

Install

pip install ferric      # Linux x86_64, CPython 3.10–3.13

The wheel needs no compiler. To change ferric itself or to use MPI, build from source; see Installation.

Each release also publishes an sdist, but it is not a self-contained build: it compiles only where libint2 (2.13.1 or the 2.7.2 export the wheels use), OpenBLAS/LAPACK, libxc, Eigen3 and a Rust toolchain are already installed (LIBINT2_PREFIX points at libint2). pip install on a platform without a wheel falls back to the sdist and fails without them. Details: Installation.

Starting with 0.1.0rc8, each GitHub release also carries a large-libint wheel per CPython (ferric-<version>-1largeam-cp3NN-...whl): the same version and commit, built against conda-forge's libint2 2.13.1 (l = 7 shells, analytic 3- and 2-centre second derivatives, G12/F12 integrals) instead of the PyPI wheel's smaller libint2. It is not a strict superset (the PyPI wheel goes higher in one-electron second derivatives), and RI Hessians do not need it. ferric.build_info()["libint_max_am"] shows which one is loaded. Details: Installation.

A first calculation

import ferric

water = ferric.Molecule.from_xyz_string(
    """3
water
O   0.000000   0.000000   0.117790
H   0.000000   0.755453  -0.471161
H   0.000000  -0.755453  -0.471161
""",
    0,
    1,
)  # charge, multiplicity

rhf = ferric.run_rhf(water, ferric.BasisSet.bundled("sto-3g"))
print(rhf.converged, f"{rhf.energy:.10f}")  # True -74.9631468000

The same calculation from the command line (ferric is installed with the wheel):

# water-rhf.toml
[molecule]
xyz = "water.xyz"

[basis]
name = "sto-3g"

[method]
kind = "rhf"

printf '3\nwater\nO 0.000000 0.000000 0.117790\nH 0.000000 0.755453 -0.471161\nH 0.000000 -0.755453 -0.471161\n' > water.xyz
OPENBLAS_NUM_THREADS=1 ferric water-rhf.toml

Continue with Your first calculation and the Sharp bits.

What it does

Which of these run from the CLI, which are Python-only, and which support open shells or gradients is tabulated in Capabilities and validation.

Implemented ≠ validated. Working code is not a checked number. Each capability is graded (Proven / Smoke / Spike) against independent references on the same page. Read it before relying on a result.

Why it exists

ferric is organized around electronic response: how the density reacts to a perturbation, the object behind polarizabilities, dielectric screening and dispersion. Attenuated MP2, PDEP-RPA/GW and constrained DFT are three ways of getting that object right where standard methods get it wrong. See Electronic response.

Building from source and contributing

git clone https://github.com/mgoldey/ferric && cd ferric
scripts/install-libint.sh ~/.local/libint2-2.13.1   # prebuilt libint2, seconds
export LIBINT2_PREFIX=~/.local/libint2-2.13.1
cargo build --release
OPENBLAS_NUM_THREADS=1 ./target/release/ferric examples/water-rhf.toml
OPENBLAS_NUM_THREADS=1 cargo test --workspace

See CONTRIBUTING.md for the development loop, the Python binding tests and the push gate.

Citing

If you use ferric, cite the software (see CITATION.cff) and the papers for the methods you ran, listed in References and citing.

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE)
• MIT license (LICENSE-MIT)

at your option.

Third-party code

crates/ferric-integrals/shim/libecpint/ vendors libecpint (MIT, Copyright (c) 2021 Robert A. Shaw); its license is retained at crates/ferric-integrals/shim/libecpint/LICENSE.

ferric links against external libraries with their own licenses, notably libint2 (LGPL-3.0-or-later), libxc (MPL-2.0), OpenBLAS/LAPACK (BSD), and optionally xtb (LGPL-3.0), which govern redistribution of binaries built against them. libint2 is a required dependency, so distributing a compiled ferric binary means distributing LGPL-linked code, which carries obligations (relinking, source availability) beyond ferric's own MIT/ Apache-2.0 terms. Building from source for your own use is unaffected.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.