CASSCFComplete Active Space Self-Consistent Field (also seen as CAS-SCF)
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These were computed at the multireference CASSCF level of theory, and the SOC values for IVa and IVb are presented in Table 1.
At those DFT-computed structures, CASSCF single point energy calculations were made to obtain the SOC values (Table 1).
Morokuma, "Multi-reference Ab initio density matrix renormalization group (DMRG) CASSCF and DMRG-CASPT2 Study on the Photochromic Ring Opening of Spiropyran," Journal of Chemical Theory and Computation, vol.
The results are interpreted in terms of the geometry of conical intersection (CI) between the first singlet ([S.sub.1]) excited state and ground state ([S.sub.0]), which was optimized by using CASSCF method.
CASSCF. Multiconfigurational self-consistent field (MCSCF) is a method in quantum chemistry used to generate qualitatively correct reference states of molecules in cases where Hartree-Fock (HF) and DFT are not adequate (e.g., for molecular ground states which are quasi-degenerate with low-lying excited states or in bond breaking situations).
In this research, the CASSCF computations used an 8electron and 8-orbital active space involving all the [pi] orbitals of benzene and ethylene moieties.
The CASSCF ab initio computations used an [pi]-electron, [pi]-orbital active space involving all the [pi]-orbitals of the benzene and ethylene moieties.
Although Robb's group had calculated this system by using CASSCF, the overlaps of ethylene moiety and benzene ring in synchronous and asynchronous mode were neglected.
However, in synchronous mode, the CI energy is even higher than the vertical excitation energy at CASSCF (8,8)/6-31G(d) level.
The CASSCF calculations present that the evolution path from FC to CI is barrierless for asynchronous mode while it has to overcome 0.8 eV barrier in synchronous addition reaction.
In this research, the CASSCF ab initio computations used a 12-electron and 12-orbital active space involving all the [pi]-orbitals of two benzene moieties.
The interatomic distances of [C.sub.1]-[C.sub.1]' and [C.sub.2]-[C.sub.2]' are 1.64 [Angstrom] and 2.60 [Angstrom], respectively, (as seen in Figure 12) by using CASSCF optimization for the [S.sub.1]/[S.sub.0] CI of two-benzene system.