Light-weight tight-binding framework

This project is an effort to create a library implementation of the extended tight binding (xTB) Hamiltonian which can be shared between xtb and dftb+. The current state of this project should be considered as highly experimental.

Goals of this project are

• create a high-level interface to the extended tight binding methods
• allow low-level access to the components forming the actual energy expression
• provide a framework to handle and manipulate parametrization data

Explicit non-goals are

• provide functionality beyond singlepoint calculations in this library (like geometry optimization or molecular dynamics)

Installation

Building from source

To build tblite from the source code in this repository you need to have a Fortran compiler supporting Fortran 2008 and one of the supported build systems:

• meson version 0.57.2 or newer, with a build-system backend, i.e. ninja version 1.10 or newer
• cmake version 3.14 or newer, with a build-system backend, i.e. ninja version 1.10 or newer
• fpm version 0.2.0 or newer

To build this project from the source code in this repository you need to have

• a Fortran compiler supporting Fortran 2008
• meson version 0.57.2 or newer
• a build-system backend, i.e. ninja version 1.10 or newer
• a LAPACK / BLAS provider, like MKL or OpenBLAS

Meson is the primary build system and provides feature-complete functionality of this project. CMake and fpm support are available but the functionality of the project is limited. Currently, tblite support GCC 8 and newer or Intel 18 and newer.

Detailed installation instruction are available in the project documentation under the installation category.

Building with meson

Optional dependencies are

• asciidoctor to build the manual page
• C compiler to test the C-API and compile the Python extension module
• Python 3.6 or newer with the CFFI package installed to build the Python API

Setup a build with

meson setup _build

You can select the Fortran compiler by the FC environment variable. To compile and run the projects testsuite use

meson test -C _build --print-errorlogs

To run the more extensive testing for the available parametrizations use

meson test -C _build --print-errorlogs --benchmark

If the testsuites pass you can install with

meson configure _build --prefix=/path/to/install
meson install -C _build

This might require administrator access depending on the chosen install prefix. For more details see the meson installation instructions.

Usage

This project provides multiple entry points for different usage scenarios. The simplest way to check out this project is by using the command line driver.

Command line interface

The tblite runner executable provides full access to the implemented Hamiltonians, with the tblite-run subcommand. You can run a single point calculation by providing a geometry input with

tblite run --method gfn2 coord

To export a parametrization use the tblite-param subcommand

tblite param --method gfn2 --output gfn2-xtb.toml

The parameter file can be inspected or modified and than used to perform single point calculations with

tblite run --param gfn2-xtb.toml coord

A preliminary interfaces for the parameter optimization is provided by the tblite-fit subcommand. By providing a external command to evaluate the data set in the input file and setting the parameters to relax the fit can be started with

tblite fit gfn2-xtb.toml input.toml

The provided external program can callback to the main program to evaluate single points or create differences between data outputs using the tblite-tagdiff subcommand. By adding the --dry-run option the setup of the parameter optimization can be inspected and with --copy copy.toml the input settings can be dumped for user inspection and tweaking.

For more details on all available subcommands checkout the tblite(1) man page and the respective subcommand man pages.

Documentation

User and developer documentation is available here.

License

This project is free software: you can redistribute it and/or modify it under the terms of the Lesser GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This project is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose. See the Lesser GNU General Public License for more details.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this project by you, as defined in the Lesser GNU General Public license, shall be licensed as above, without any additional terms or conditions.