Alternatively, effective dynamic correlation can be introduced into the RAS-CI wave function
by means of short-range density functional correlation energy.
The idea relies on the different ability of wave function methods and DFT to treat
non-dynamic and dynamic correlations.
Concretely, the RAS-CI-DFT (or RAS-DFT) method
J. Chem. Phys.
(2018), 148, pp. 124118. is based on the range separation of the electron-electron Coulomb operator () through the error function to describe long-range interactions,
where is the inter electronic distance and the parameter controls the extend of short- and long-range interactions. Such splitting of provides a well-defined approach to merge WFT with DFT by applying to RAS-CI and to DFT. Within the RAS-DFT approach, the energy of an electronic state can be expressed as: