Different DFT-Based Methods Used in the Study of Excited States

1 Different DFT-Based Methods Used in the Study of Excited States 

As we have seen in Sect. 2, KS-DFT has been very successful in dealing with ground state properties, especially for closed shell molecules. KS-DFT owes this 

The ADFT/ASCF-DFT scheme has been met with considerable reservation. Thus, ADFT/ASCF-DFT assumes implicitly that a transition can be represented by an excitation involving only two orbitals, an assumption that seems not generally to be satisfied. Also, the variational optimization in ASCF-DFT of the orbitals makes it difficult to ensure orthogonality between different excited state determinants when many transitions are considered, resulting ultimately in a variational collapse. Finally, it has been questioned [110] whether there exists a variational principle for excited states in DFT. In spite of this, some of the first pioneering chemical applications of DFT involved ASCF-DFT calculations on excitation energies [36, 113-116] for transition metal complexes and ASCF-DFT is still widely used [117-121]. 

A popular alternative to variational approaches in the study of excited state properties is time-dependent DFT (TD-DFT) in its adiabatic formulation [122-128]. In this scheme, one considers the first-order change in the ground state density (co. r) due to a perturbation from the 7-component Ey(co) of a frequency-dependent electric field and the associated frequency-dependent polarizability ocyP(co). The excitation energies ojq are subsequently found as poles or resonances for ocy (co). 

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