Basis functions used in any ab initio calculation, whether they concern solids or molecules, are the algebraic pillars of the electronic wave function whenever the Schrödinger equation has to be solved numerically. Gaussian-type orbitals (GTOs) are by far the most popular basis functions in quantum chemistry due to their atomically localized analytical forms that allow for an efficient evaluation of the multi-electron integrals appearing in wavefunction-based methods and, to a lesser extent, in Kohn-Sham density functional theory (DFT) .