The most common form of MC-NCFT utilizes nonclassical-energy functionals obtained by translating Kohn-Sham exchange-correlation functionals for use with multiconfigurational wave functions via the on-top pair density and is called multiconfiguration pair-density functional theory (MC-PDFT). The translated PBE functional (tPBE) has been used as the functional in the majority of MC-PDFT calculations to date. The nonclassical energy from a density functional can be mixed with the nonclassical part of the CASSCF energy to form a "hybrid" nonclassical functional, for example, using a 0.75:0.25 mixture of tPBE and CASSCF nonclassical energies yields the tPBE0 functional. Difficulties encountered in all such post-CASSCF methods are making the active space large enough and well-balanced enough to converge to a qualitatively accurate description of the underlying wave function(s). The results can depend significantly on the size and nature of the active space and the initial orbital guess. Moreover, in many occasions the orbitals will change character during their optimization. For these reasons, such calculations often require expert human guidance to carefully choose the active space size and composition and monitor them during the calculations.