Excited Kohn-Sham determinants

How can we obtain an energy for the excited singlet The normal prescription is not applicable since there is no single determinant on which a Kohn-Sham calculation could be based. However, the determinant that intuitively comes closest to this state is... 

One important application of TDDFT is to compute low lying excited electronic states and energies. Simpler approaches, in which the virtual ground state Kohn-Sham orbitals and energies are determined as an estimate for excited states are often not sufficiently accurate for chemical applications and can only be used as a rather qualitative indication. 

In the present chapter, we will focus on the simulation of the dynamics of photoexcited nucleobases, in particular on the investigation of radiationless decay dynamics and the determination of associated characteristic time constants. We use a nonadiabatic extension of ab initio molecular dynamics (AIMD) [15, 18, 21, 22] which is formulated entirely within the framework of density functional theory. This approach couples the restricted open-shell Kohn-Sham (ROKS) [26-28] first singlet excited state, Su to the Kohn-Sham ground state, S0, by means of the surface hopping method [15, 18, 94-97], The current implementation employs a plane-wave basis set in combination with periodic boundary conditions and is therefore ideally suited to condensed phase applications. Hence, in addition to gas phase reference simulations, we will also present nonadiabatic AIMD (na-AIMD) simulations of nucleobases and base pairs in aqueous solution. 

In this section we first review briefly the formal connection between properties of the one- and two-particle Green s function and elementary excitations. Determining the partition function we then work out interrelations between the Kohn-Sham equation of density-functional theory and the general many-body perturbation theory for the exact exchange-correlation energy. 

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