Metadata-Version: 2.2
Name: gfnff
Version: 0.3.0
Summary: Python bindings for the GFN-FF force-field library
Keywords: force field,GFN-FF,computational chemistry
Author-Email: Philipp Pracht <research@philipp-pracht.de>
License:                    GNU LESSER GENERAL PUBLIC LICENSE
                                Version 3, 29 June 2007
         
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Classifier: Intended Audience :: Science/Research
Classifier: License :: OSI Approved :: GNU Lesser General Public License v3 or later (LGPLv3+)
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Fortran
Classifier: Topic :: Scientific/Engineering :: Chemistry
Project-URL: Homepage, https://github.com/pprcht/gfnff
Project-URL: Repository, https://github.com/pprcht/gfnff
Requires-Python: >=3.9
Requires-Dist: numpy>=1.21
Provides-Extra: ase
Requires-Dist: ase>=3.22; extra == "ase"
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Requires-Dist: ase>=3.22; extra == "docs"
Description-Content-Type: text/markdown

<div align="center">

<h1>GFN-FF</h1>
<h3>A general force field for elements <i>Z</i> = 1–103</h3>

[![build status](https://github.com/pprcht/gfnff/actions/workflows/build-and-test.yml/badge.svg)](https://github.com/pprcht/gfnff/actions/workflows/build-and-test.yml)
[![PyPI version](https://img.shields.io/pypi/v/gfnff.svg)](https://pypi.org/project/gfnff/)
[![conda-forge version](https://img.shields.io/conda/vn/conda-forge/gfnff.svg)](https://anaconda.org/conda-forge/gfnff)
[![Documentation](https://img.shields.io/badge/docs-pprcht.github.io%2Fgfnff-blue.svg)](https://pprcht.github.io/gfnff/)
[![License: LGPL v3](https://img.shields.io/badge/license-LGPL_v3-coral.svg)](https://www.gnu.org/licenses/lgpl-3.0)

</div>

A standalone library implementation of the **GFN-FF** method by S. Spicher and S. Grimme,
adapted from the [`xtb`](https://github.com/grimme-lab/xtb) code (most recently at commit
[`6d44803`](https://github.com/grimme-lab/xtb/commit/6d44803) and validated against that version's results).
It is meant to be linked into other Fortran, C, and C++ projects, and it also ships Python bindings.
From this point forward, development may diverge from the upstream `xtb` implementation.
As of version `v0.3.0` of this repository divergence is the case in order to add analytical Hessians and other features.

GFN-FF (*Geometries, Frequencies, Non-covalent interactions Force-Field*) is a
completely automated, topology-based force field for fast structure optimisations
and non-covalent interaction energies.
The topology and parametrisation are derived entirely from the input geometry,
without user-defined atom types or connectivity.

## Quick start

```bash
pip install "gfnff[ase]"
```

```python
from ase.build import molecule
from gfnff import GFNFF

atoms = molecule("caffeine")
atoms.calc = GFNFF()

energy = atoms.get_potential_energy()   # eV
forces = atoms.get_forces()             # eV / Å
```

The same install provides a command-line tool:

```bash
gfnff molecule.xyz --opt --alpb h2o
```

## Documentation

The documentation is hosted at <https://pprcht.github.io/gfnff/>.
It contains the guides listed below and a Python API reference generated from the docstrings.

| Topic | Page |
|---|---|
| Fortran, C and C++ interfaces, periodic systems, use as a CMake or Meson subproject | [docs/library.md](docs/library.md) |
| Python: installation, command-line tool, `GFNFFCalculator`, ASE calculator, Hessians | [docs/python.md](docs/python.md) |
| Force-field versions, `conformer2020`, custom parameter files, user-supplied molecular graphs | [docs/parametrisation.md](docs/parametrisation.md) |
| Benchmarks and choice of BLAS backend | [docs/performance.md](docs/performance.md) |
| TOML parameter file format | [param/README.md](https://github.com/pprcht/gfnff/blob/master/param/README.md) |
| Python API reference | [pprcht.github.io/gfnff](https://pprcht.github.io/gfnff/package_reference.html) |

## Building from source

The library requires a Fortran and C compiler (e.g. `gfortran`/`gcc`),
LAPACK/BLAS (e.g. OpenBLAS), and optionally OpenMP.
Both CMake (≥ 3.21) and Meson (≥ 0.59) are supported.

| | CMake | Meson |
|---|---|---|
| Build | `cmake -B _build`<br>`cmake --build _build` | `meson setup _build`<br>`ninja -C _build` |
| Test | `cmake -B _build -DWITH_TESTS=ON`<br>`cmake --build _build`<br>`ctest --test-dir _build` | `meson setup _build -Dtests=true`<br>`ninja -C _build test` |

The compiled library (`libgfnff.a` by default) is placed in the build directory
and can be linked into any downstream project.

## Using the library

Initialise a calculator once (topology setup, the expensive step), then call the
singlepoint routine as often as needed:

```fortran
use gfnff_interface
type(gfnff_data) :: calc

call calc%init(nat, at, xyz, ichrg=ichrg, iostat=io)
call calc%singlepoint(nat, at, xyz, energy, gradient, iostat=io, sigma=sigma)
call calc%deallocate()
```

Coordinates are in Bohr, energies in Hartree, gradients in Eh/Bohr.
The C/C++ header `include/gfnff_interface_c.h` mirrors these calls;
see [docs/library.md](docs/library.md).

## Performance

![GFN-FF benchmark](assets/benchmark.png)

Caffeine clusters from 24 to 1536 atoms on 8 cores.
Energy and gradient are 1.2–1.6x faster than the pre-refactor code from 192 atoms upwards,
and the analytic Hessian is 28x (24 atoms) to 59x (768 atoms) faster than finite differences.
Hessian speed depends mainly on the BLAS backend; details are in
[docs/performance.md](docs/performance.md).

## References

- **Molecular GFN-FF**, a generic, partially polarisable force field covering organic,
  organometallic, and biochemical systems:
  S. Spicher, S. Grimme, *Angew. Chem. Int. Ed.* **2020**, 59, 15665.
  [doi:10.1002/anie.202004239](https://doi.org/10.1002/anie.202004239)
- **Periodic boundary conditions and molecular crystals**, with adjusted non-covalent
  interactions for lattice energies and unit-cell optimisations:
  S. Grimme, T. Rose, *Z. Naturforsch. B* **2024**, 79, 191.
  [doi:10.1515/znb-2023-0088](https://doi.org/10.1515/znb-2023-0088)
- **Lanthanide and actinide extension**, a reparametrised f-element treatment:
  T. Rose, M. Bursch, J.-M. Mewes, S. Grimme, *Inorg. Chem.* **2024**.
  [doi:10.1021/acs.inorgchem.4c03215](https://doi.org/10.1021/acs.inorgchem.4c03215)

## License

This project is licensed (as the original `xtb` code) under the **GNU Lesser General Public License v3** or later.
See [`LICENSE`](https://github.com/pprcht/gfnff/blob/master/LICENSE) for details.
