I want to calculate transient absorption spectra with TDDFT results.
That really depends on the processes that occur in your system. Do you want to compute ultrafast spectra in molecular systems (dimers, trimers,...)? These may be effected by excitation energy transfer (EET) and/or electron transfer (ET) within your system. You may use TDDFT calculations in order to calculate the respective ET or EET couplings (as input for further computations).
We did (so far) MD/TDDFT-based studies of transient absorption in molecular systems where only EET occurs (EET is much faster compared to the lifetime of excitation). However, if you know the conformation of your system (and it is stable), you do not need to carry out MD simulations. You determine the transfer couplings (couplings of transition densities, available from TDDFT calculations) and therefrom the EET rates (in Foerster-approximation), and solve rate equations for the excited state populations (if the couplings are smaller than 10-20 meV). Your initial conditions depend on the transition dipole moments of your molecules and the polarization of the pump pulse. Then, in approximation, you may obtain the delay-time dependent transient anisotropy from your calculated EET-dynamics.
However, depending on the processes that actually occur in your systems calculation of transient absorption is a quite complex task.
thank you for your answer. how can i calculate "the transfer couplings (couplings of transition densities from tddft calculation" ? and how can i determine EET rate and solve rate equations for the excited state populations? thanks
Therefore I have to point you to the respective literature. For example, transition densities can be computed utilizing Gaussian09. Foerster theory is standard for computation of EET. Above, I only explained the principal idea.
thanks, i got your paper : Transient absorption spectra of excitation energy transfer in supramolecular complexes: A mixed quantum-classical description of pheophorbide- a systems. I am studying this paper and its useful for me. thank you
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