Full Optimized Reaction Space

The method is also called FORS (full optimized reaction space). 

The major problem with MCSCF methods is selecting the necessary configurations to include for the property of interest. One of the most popular approaches is the Complete Active Space Self-consistent Field (CASSCF) method (also called Full Optimized Reaction Space, FORS). Here the selection of configurations is done by partitioning the MOs into active and inactive spaces. The active MOs will typically be some of the dii rest occupied and some of the lowest unoccupied MOs from a RHF calculationr Fhe-daactive MOs either have 2 or 0 electrons, i.e. always doubly occupied or empty. Within... 

Diels-Alder reaction, 304, 350, 358 Ensemble, 375, 377 Full Optimized Reaction Space (FORS), 119 Heitler-London (HL) function, in valence... 

An important issue in MCSCF calculations is the selection of the configurations to be included in the wavefunction expansion. The most popular approach is the complete active space self-consistent field (CASSCF) method, also called full optimized reaction space (FORS). This approach starts Irom a zeroth order set of MOs, usually obtained via the Hartree-Fock method. The set of MOs is split into three subsets, as illustrated in Fig. 2.3. A first one containing occupied inactive orbitals, for which the occupation numbers are fixed to 2. A second one containing active orbitals, including both occupied and virtual orbitals of the reference Hartree-Fock configuration, in which all possible electron excitations are allowed. And a third one containing virtual inactive orbitals, for which the occupation numbers are fixed to 0. 

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