TREXIO

TREXIO is an open-source file format and library developed for the storage and manipulation of data produced by quantum chemistry calculations. It is designed with the goal of providing a reliable and efficient method of storing and exchanging wave function parameters and matrix elements, making it an important tool for researchers in the field of quantum chemistry. In this work, we present an overview of the TREXIO file format and library. The library consists of a front-end implemented in the C programming language and two different back-ends: a text back-end and a binary back-end utilizing the HDF5 library which enables fast read and write operations. It is compatible with a variety of platforms and has interfaces for the Fortran, Python, and OCaml programming languages. In addition, a suite of tools has been developed to facilitate the use of the TREXIO format and library, including converters for popular quantum chemistry codes and utilities for validating and manipulating data stored in TREXIO files. The simplicity, versatility, and ease of use of TREXIO make it a valuable resource for researchers working with quantum chemistry data.

Minimal requirements (for users):

• Autotools (autoconf >= 2.69, automake >= 1.11, libtool >= 2.2) or CMake (>= 3.16)
• C compiler (gcc/icc/clang)
• Fortran compiler (gfortran/ifort)
• HDF5 library (>= 1.8) [optional, recommended for high performance]

Installation procedure from the tarball (for users):

1. Download the trexio-<version>.tar.gz file
2. gzip -cd trexio-<version>.tar.gz | tar xvf -
3. cd trexio-<version>
4. ./configure
5. make -j`getconf _NPROCESSORS_ONLN`
6. make -j`getconf _NPROCESSORS_ONLN` check
7. sudo make install

Note: on systems with no sudo access, one can replace ./configure with ./configure prefix=${PWD}/build in order to execute make install/uninstall commands without sudo privileges.

Note: when linking against an MPI-enabled HDF5 library one usually has to specify the MPI wrapper for the C compiler by adding, e.g., CC=mpicc to the ./configure command.

Additional requirements (for developers):

• python3 (>= 3.6)
• Emacs (>= 26.0)
• SWIG (>= 4.0) [required for the Python API]

Note: The source code is auto-generated from the Emacs org-mode (.org) files following the literate programming approach. This is why the src directory is initially empty.

Installation procedure from the GitHub repo clone (for developers):

1. git clone https://github.com/TREX-CoE/trexio.git
2. cd trexio
3. ./autogen.sh
4. ./configure
5. make -j`getconf _NPROCESSORS_ONLN`
6. make -j`getconf _NPROCESSORS_ONLN` check
7. sudo make install

Installation procedure for CMake users (from the tarball or GitHub repo clone):

The aforementioned instructions rely on Autotools build system. CMake users can achieve the same with the following steps (an example of out-of-source build):

1. cmake -S. -Bbuild
2. cd build
3. make -j`getconf _NPROCESSORS_ONLN`
4. ctest -j`getconf _NPROCESSORS_ONLN`
5. sudo make install

Note: on systems with no sudo access, one can add -DCMAKE_INSTALL_PREFIX=build as an argument to the cmake command so that make install/uninstall can be run without sudo privileges.

Note: when linking against an MPI-enabled HDF5 library one usually has to specify the MPI wrapper for the C compiler by adding, e.g., -DCMAKE_C_COMPILER=mpicc to the cmake command.

Installation procedure for conda users

The official releases of TREXIO >2.0.0 are also available via the conda-forge channel. The pre-compiled stable binaries of trexio can be installed as follows:

conda install -c conda-forge trexio

More details can be found in the corresponding trexio-feedstock. Note that both parallel (see mpi_openmpi prefix) and serial (nompi) variants are provided.

Installation procedure for Guix users

The official releases of TREXIO >=2.0.0 can be installed using the GNU Guix functional package manager. The trexio.scm Schema file contains the manifest specification for the trexio package. It can be installed as follows:

guix package --cores=`getconf _NPROCESSORS_ONLN` --install-from-file=trexio.scm

Installation procedure for Spack users

The official releases >=2.0.0 and the development version of TREXIO can be installed using the Spack package manager. The trexio/package.py file contains the Spack specifications required to build different variants of trexio library. It can be installed as follows

spack install --jobs `getconf _NPROCESSORS_ONLN` trexio

Installation procedure for Debian/Ubuntu users

The official release of TREXIO 2.2.0 is available as a Debian (.deb) package thanks to the Debichem Team. The source code is hosted here and the pre-built binary files are available via the Debian package registry.

TREXIO is also available on Ubuntu 23.04 (Lunar Lobster) and newer and can be installed as follows:

sudo apt-get update && sudo apt-get install libtrexio-dev

Compilation without the HDF5 library

By default, the configuration step proceeds to search for the HDF5 library. This search can be disabled if HDF5 is not present/installable on the user machine. To build TREXIO without HDF5 back end, append --without-hdf5 option to configure script or -DENABLE_HDF5=OFF option to cmake. For example,

• ./configure --without-hdf5
• cmake -S. -Bbuild -DENABLE_HDF5=OFF

Linking to your program

The make install command takes care of installing the TREXIO shared library on the user machine. After installation, append -ltrexio to the list of compiler ($LIBS) options.

In some cases (e.g. when using custom installation prefix during configuration), the TREXIO library might end up installed in a directory, which is absent in the default $LD_LIBRARY_PATH. In order to link the program against TREXIO, the search path can be modified as follows:

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:<path_to_trexio>/lib

where the <path_to_trexio> has to be replaced by the prefix used during the installation.

If your project relies on CMake build system, feel free to use the FindTREXIO.cmake module to find and link TREXIO library automatically.

In Fortran applications, make sure that the trexio_f.f90 module file is included in the source tree. You might have to manually copy it into your program source directory. The trexio_f.f90 module file can be found in the include/ directory of the TREXIO source code distribution.

Note: there is no need to include trexio.h header file during compilation of Fortran programs. Only the installed library and the Fortran module file are required.

Naming convention

The primary TREXIO API is composed of the following functions:

• trexio_open
• trexio_write_[group]_[variable]
• trexio_read_[group]_[variable]
• trexio_has_[group]_[variable]
• trexio_close

where [group] and [variable] substitutions correspond to the contents of the trex.json configuration file (for more details, see the corresponding documentation page). For example, consider the coord variable (array), which belongs to the nucleus group. The TREXIO user can write or read it using trexio_write_nucleus_coord or trexio_read_nucleus_coord functions, respectively.

Note: the [variable] names have to be unique only within the corresponding parent [group]. There is no naming conflict when, for example, num variable exists both in the nucleus group (i.e. the number of nuclei) and in the mo group (i.e. the number of molecular orbitals). These quantities can be accessed using the corresponding trexio_[has|read|write]_nucleus_num and trexio_[has|read|write]_mo_num, respectively.

Python API

For more details regarding the installation and usage of the TREXIO Python API, see this page.

The aforementioned instructions are adapted for users installing from the source code distribution (periodically updated). In order to install the Python API with the latest changes, follow the developer installation guide and run the following command in the end

make python-install

**Note: this implies that both SWIG is installed and available.

We rely on the pytest package for unit testing. It can be installed via pip install pytest. To test the installation, run

make python-test

We highly recommend to use virtual environments to avoid compatibility issues and to improve reproducibility.

Tutorial

TREXIO tutorials in Jupyter notebook format can be found in the corresponding GitHub repository or on Binder.

For example, the tutorial covering TREXIO basics using benzene molecule as an example can be viewed and executed online by clicking on this badge:

Documentation

Documentation generated from TREXIO org-mode files.

Citation

The journal article reference describing TREXIO can be cited as follows:

@article{10.1063/5.0148161,
    author = {Posenitskiy, Evgeny and Chilkuri, Vijay Gopal and Ammar, Abdallah and Hapka, Michał and Pernal, Katarzyna and Shinde, Ravindra and Landinez Borda, Edgar Josué and Filippi, Claudia and Nakano, Kosuke and Kohulák, Otto and Sorella, Sandro and de Oliveira Castro, Pablo and Jalby, William and Ríos, Pablo López and Alavi, Ali and Scemama, Anthony},
    title = "{TREXIO: A file format and library for quantum chemistry}",
    journal = {The Journal of Chemical Physics},
    volume = {158},
    number = {17},
    year = {2023},
    month = {05},
    issn = {0021-9606},
    doi = {10.1063/5.0148161},
    url = {https://doi.org/10.1063/5.0148161},
    note = {174801},
    eprint = {https://pubs.aip.org/aip/jcp/article-pdf/doi/10.1063/5.0148161/17355866/174801\_1\_5.0148161.pdf},
}

Journal paper:

ArXiv paper:

Miscellaneous

The code should be compliant with the C99 CERT C coding standard. This can be checked with the cppcheck tool.

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TREX: Targeting Real Chemical Accuracy at the Exascale project has received funding from the European Union’s Horizon 2020 - Research and Innovation program - under grant agreement no. 952165. The content of this document does not represent the opinion of the European Union, and the European Union is not responsible for any use that might be made of such content.