Time-dependent density functional theory performance

Since DFT calculations are in principle only applicable for the electronic ground state, they cannot be used in order to describe electronic excitations. Still it is possible to treat electronic exciations from first principles by either using quantum chemistry methods [114] or time-dependent density-functional theory (TDDFT) [115,116], First attempts have been done in order to calculate the chemicurrent created by an atom incident on a metal surface based on time-dependent density functional theory [117, 118]. In this approach, three independent steps are preformed. First, a conventional Kohn-Sham DFT calculation is performed in order to evaluate the ground state potential energy surface. Then, the resulting Kohn-Sham states are used in the framework of time-dependent DFT in order to obtain a position dependent friction coefficient. Finally, this friction coefficient is used in a forced oscillator model in which the probability density of electron-hole pair excitations caused by the classical motion of the incident atom is estimated. 

The very first application of time dependent density functional theory to molecular electronics was performed by Tomfohr and Sankey in 2001 [14], The basic equations of motion solved in that work are the usual Kohn-Sham (KS) equations of TDDFT. 

Rohrdanz MA, Martins KM, Herbert JM (2009) A long-range-corrected density functional that performs weU for both ground-state properties and time-dependent density functional theory excitation energies, including charge-transfer excited states. J Chem Phys 130 054112... 

Consequently, DFT is restricted to ground-state properties. For example, band gaps of semiconductors are notoriously underestimated [142] because they are related to the properties of excited states. Nonetheless, DFT-inspired techniques which also deal with excited states have been developed. These either go by the name of time-dependent density-functional theory (TD-DFT), often for molecular properties [147], or are performed in the context of many-body perturbation theory for solids such as Hedin s GW approximation [148]. 

Recently, an extensive study on the photoexcitation and isomerization of PYP was published. In this study, a combination of molecular dynamics simulation techniques and time-dependent density functional theory calculations were used. Several interesting results were obtained. Out of five separate simulations that were performed of the excited state, two showed a twisted configuration of the chromophore, and in three, the chromophore retained its trans configuration. This could explain the two different excited states observed in the ultrafast absorption measurement (see above). 

Correlated dynamic NLO responses can also be computed using the time-dependent density functional theory (TDDFT) method, whose basic equations are similar to those of TDHF. However, conventional exchange - correlation (XC) functionals suffer from severe drawbacks when computing the NLO properties of extended systems [56], as well as when evaluating the /I contrast in molecular NLO switches. The values collected in Table 8.1 illustrate the performance of XC functionals to provide a balanced description of the static HRS hyperpolarizabilities of the two tautomeric forms of compound 11, compared to reference MP2 calculations. 

Sychrovsky et performed, for the first time, a complete implementation of coupled perturbed density functional theory (CPDFT) for the calculation of spin-spin coupling constants with pure and hybrid DFT. They analyzed the dependence of DFT with respect to the calculation of coupling constants on the exchange-correlation (XC) functionals used. They demonstrated the importance of electron correlation effects and showed that the hybrid functional leads to the best accuracy of calculated spin-spin... 

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