What is TDDFT approximation useful for? Is it implemented in SIESTA?
Time-Dependent DFT can be used to calculate excitonic binding energies, frequency-dependent response properties and photoabsorption spectra.
The present TDDFT implementation in Siesta is in real time (time evolution) as opposed to the linear-response frequency-dependent TDDFT. This approach allows to go beyond linear response. The method is described in the following article, "Calculation of the optical response of atomic clusters using time-dependent density functional theory and local orbitals”. Argyrios Tsolakidis, Daniel Sánchez-Portal and Richard M. Martin, PHYSICAL REVIEW B 66, 235416 2002.
This approach includes the corrections given by the XC kernel (some excitonic correction) which tend to RPA for infinite systems.
Improvements on the TDDFT implementation are under current depelopment within the SIESTA-PRO project.