Range‐separated multiconfigurational density functional theory methods

Range-separated multiconfigurational density functional theory (RS MC-DFT) rigorously combines density functional (DFT) and wavefunction (WFT) theories. This is achieved by partitioning of the electron interaction operator into long- and short-range components and modeling them with WFT and DFT, respectively. In contrast to other methods, mixing wavefunctions with density functionals, RS MC-DFT is free from electron correlation double counting. The general formulation of RS MC-DFT allows for merging any ab initio approximation with density functionals. Implementations of RS MC-DFT aim at increasing both versatility and accuracy of the underlying methods, while reducing the computational cost of the ab initio problem. Variants of the RS MC-DFT approach can be divided into single-determinant-based range-separated methods and range-separated multideterminantal WFT methods. In these approaches the electron correlation energy is described both by a pertinent short-range density functional and by the wavefunction theory. We review the short-range functionals and correlated wavefunction theories employed in the framework of RS MC-DFT. We discuss applications of the RS MC-DFT methods to ground-state properties of molecules and to noncovalent interactions. Time-dependent linear-response theory and direct approaches to excited states are also presented. For each area of applications, we assess advantages of RS MC-DFT over conventional DFT and ab initio methods.