Over the past several decades, hundreds of XC functionals have been developed with the aim to capture all relevant physics and achieve chemical accuracy over a broad range of molecules, materials, and organometallic systems. To classify the growing number of functionals, John P. Perdew proposed a hierarchy called Jacob's ladder , which organizes functionals based on their complexity. The ladder consists of five rungs: (1) Local Density Approximations (LDA) depend only on the electron density at a given point in space and offer computational efficiency but often lack accuracy . (2) Generalized Gradient Approximations (GGA) functionals incorporate the (local) electron density and its gradient . (3) Meta-GGA functionals account for the electron density, its gradient, and the kinetic energy density . (4) Hybrid functionals mix a portion of Hartree-Fock (HF) exact exchange with XC terms from DFT , and (5) Double-hybrid and RPA-based functionals (rung-5), the highest rung on the ladder, combine a hybrid functional with post-HF correlation corrections, e.g., within second-order perturbation theory (MP2) or non-local correlation based on the random phase approximation (RPA) . As one moves up the ladder, the functionals globally tend to provide better descriptions of electronic interactions and improve the overall predictive accuracy . However, this comes at the price of an increasingly higher computational cost: for instance, the cost of hybrids is roughly two orders of magnitude the one of GGA functionals .