Jacob’s Ladder is a conceptual framework that categorizes exchange-correlation functionals based on their complexity and accuracy. It illustrates a hierarchy of functionals, starting from simpler forms like the Local Density Approximation (LDA) at the bottom, to more sophisticated approaches like Generalized Gradient Approximation (GGA) and hybrid functionals higher up the ladder. Each rung represents an increase in the functional’s ability to accurately describe electronic interactions, guiding researchers in choosing the appropriate functional for their calculations based on the desired balance between accuracy and computational efficiency