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\section{What are correlated materials?} materials}  \label{sec:correlations}  Correlated materials are compounds where the constituent electrons cannot be effectively described as non-interacting particles, namely the behavior of each electron is strongly correlated with the behavior of others.  However, to a DFT practitioner, this conceptual definition is not very useful.  In this article, we adopt a definition of correlations most applicable for a practitioner of electronic structure calculations.  DFT is a workhorse of the materials science community, providing efficient and accurate computations of the total energy and distribution of electrons of a compound, requiring only the coordinates of the atoms in its crystal lattice as input. From the total energy, one can obtain lattice constants, equations of state and the spectrum of lattice vibrations. Furthermore, one can obtain electronic properties such as band gaps, electric polarization and topological numbers, which are by no means trivial for these "simple" compounds.  The conceptual idea behind DFT is that for ground state properties, we can use