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Motivation for the ACT
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The fundamental motivation for the development of the ACT are given in these reviews :cite:p:`Spoel2003a,Lange2010a,HZhang2018a,Bashardanesh2018b,Spoel2021a,Spoel2022a,Kriz2023a`.
Milestones on the way to a new family of physics-based force fields are given below.:

* A long series of benchmarks of force fields :cite:p:`Caleman2012a,Fischer2015a,JZhang2015a,JZhang2016a,Spoel2018a,LSchmidt2023a,Hosseini2023a`.
* Databases of quantum-chemical data produced as part of the Alexandria project: enthalpies of formation and thermochemistry :cite:p:`Ghahremanpour2016a` applied to force fields here :cite:p:`Spoel2018a`.
* The Alexandria Library with more quantum-chemistry data :cite:p:`Ghahremanpour2018a,Ghahremanpour2017a`.
* A phase-transferable force field for alkali halides :cite:p:`Walz2018a` with applications towards prediction of melting points and conductivities for alkali halide liquids and mixtures :cite:p:`Walz2019a,Walz2019b,Walz2019c,Walz2021a`.
* A new potential for treating the angle in linear molecules :cite:p:`Spoel2020a`.
* New models for noble gases including accurate simulations of the melting point of solid noble gases :cite:p:`Kriz2024a`.
* Use of symmetry-adapted perturbation theory for a study of exchange around a water molecule :cite:p:`Kriz2024b`.
* An evaluation of potentials for chemical bonds in molecules :cite:p:`Maaren2025a`.


The remainder of this document contains first the User Manual, describing installation and practical usage of the ACT including the properties that can be predicted by the ACT software and Alexandria force fields.

The second part is the Reference Manual which presents, somewhat rudimentary at the time of writing, the physical foundation of the ACT models and the algorithms for training force fields.


Happy force field designing!