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Current research in the area covers a broad range of aspects of electronic structure simulations: the development of novel theoretical frameworks, new or improved methods to calculate properties within existing theories, or even more efficient and scalable algorithms. In most cases, this theoretical work requires the development of test implementations to assess the properties and predictive power of the new methods.   Given the experimentative nature of the development of methods for the simulations of electrons, the translation to code of new theory needs to be easy to implement and to modify. This is a factor that is not usually considered whenanalyzing and  comparing the broad range of methods and codes used by chemists, physicists and material scientists. The most popular representations for electronic structure rely on basis sets that usually have a certain physical connection to the system being simulated. In chemistry, the method of choice is to use atomic orbitals as a basis to describe the orbitals of a molecule. When these atomic orbitals are expanded in Gaussian functions, it leads to an efficient method as many integrals can be calculated from analytical formulae~\cite{szabo1996modern}. In condensed-matter physics, the traditional basis is a set of plane waves, which correspond to the eigenstates of a homogeneous electron gas. These physics-inspired basis sets have, however, some limitations. For example, it is not trivial to simulate crystalline systems using atomic orbitals~\cite{Dovesi_2014}, and, on the other hand, in plane-wave approaches finite systems must be approximated as periodic systems using a supercell approach.