.. include:: /substitutions.rst

.. _license:

===================
License information
===================

ViPErLEED
#########

:term:`ViPErLEED` is released as open-source under the :term:`GPLv3` (or later)
license.
Copyright (c) 2019–2024, ViPErLEED Developers.

The ViPErLEED project aims to provide free and open software.
However, because ViPErLEED is building on existing software, the
ViPErLEED developers cannot grant permission to redistribute certain parts
of the software. For inquiries or questions, please contact the ViPErLEED
developers under info@viperleed.org.

All files in the main repository and all files authored by the ViPErLEED
developers are licensed under the :term:`GPLv3`. This explicitly includes
the ViPErLEED Python package (|calc|, ``gui``, ``utils``), ViPErLEED
electronics (firmware, schematics, software) and the ViPErLEED :term:`ImageJ`
plugins.

The documentation for all parts of ViPErLEED is licensed under the
:term:`CC BY 4.0` license.


TensErLEED
##########

The v1.2 version of TensErLEED was published with the
`Computer Physics Communications User License <https://www.elsevier.com/about/policies/open-access-licenses/elsevier-user-license/cpc-license>`__
, which **requires** users to reference the original article
(:cite:t:`blumFastLEEDIntensity2001a`) in resulting publications.

*The ViPErLEED developers have obtained explicit permission by the authors to
use and distribute these codes as part of ViPErLEED.
Others may not redistribute TensErLEED, without permission by the original
authors.*

Changes to the TensErLEED source code made by the ViPErLEED authors (i.e. the
patches that constitute v1.6.1 onwards), are licensed under GPLv3 or later.
The copyright to these changes remains with the ViPErLEED authors.

EEASISSS
########

Elastic Electron-Atom Scattering in Solids and Solid Surfaces (EEASISSS)
is written and maintained by John O. Rundgren (jru@KTH.se) and used by
ViPErLEED with permission by the author.

The author appreciates acknowledgement in publications by citation of
the relevant works:
:cite:t:`rundgrenLowenergyElectronDiffraction2021`,
:cite:t:`rundgrenElasticElectronatomScattering2007`,
:cite:t:`zrdz<rundgrenOptimizedSurfaceslabExcitedstate2003>`.


Local-density-functional calculations of the energy of atoms
############################################################

The program "Local-density-functional calculations of the energy of
atoms" (``viperleed-tensorleed/atomic_density_files/atomic.f``) was written
by Eric L. Shirley (NIST). The ViPErLEED authors have obtained
permission from the author to include the program in the ViPErLEED
package and release it under :term:`GPLv3` (or later). The copyright remains
with Eric L. Shirley.

If you find this program useful in your research, the author appreciates
acknowledgement by including the following attribution in resulting
publications:

 **Eric L. Shirley, PhD Thesis, University of Illinois at Urbana-Champaign, 1991**