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The development of theoretical methods for the simulation of electronic system is an active area of study. This interest has been fueled, on one hand, by the success of theoretical tools like density functional theory (DFT)~\cite{Hohenberg_1964,Kohn_1965}, that can predict many properties with good accuracy at a relatively modest computational cost. On the other hand, these same tools are not good enough for many applications, and more accurate and more efficient methods are required.  Current research is targeted on a broad range of aspects of electronic structure simulations: the development of new theoretical frameworks, new or improved methods to calculate properties within existing theories, or even new, more efficient, efficient or 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 when analyzing and comparing the broad range of methods and codes used by chemists, phyisicst and material scientist. The most popular representations rely on basis sets, that usually have a certain physical connection to the system being simulated.