where the classical energy E MC class contains the nucleus-nucleus repulsion, nucleus-electron attraction, classical electron-electron repulsion, and electronic kinetic energy. The nonclassical functional E nc depends on a featurization f of the reference wave function ψ MC , which may be the density, on-top density, and their gradients, or other attributes of the wave function -it can, for example, be the on-top functional E ot . MC-PDFT does not use wavefunction theory for the internal correlation energy. The method has shown promising performances in several applications involving ground and excited states of multireference systems. Analytic gradients for the state-specific and state-average formulations are available. There are two main issues that should be addressed in the future, if MC-PDFT is to become a routine method for multireference systems: