Franck-Condon Herzberg-Teller approximation

Within this approximation the transition occurs between vibrational states with the highest overlap. Moreover, electric dipole forbidden transitions (i.e. when /tnm(QQ " ) = 0) cannot be described within this approximation. They can be treated however by considering the expansion in Eq. (4.18) to first order, which yields the Franck-Condon-Herzberg-Teller approximation [58, 61]. 

Additionally, various approximations on the transition dipole moment, namely Franck-Condon (FC), Herzberg-Teller (HT), or Franck-Condon Herzberg-Teller (FCHT) can be appfied. From the computational perspective, the state-of-the-art methods rooted into TD-DFT are nowadays the most effective routes to treat medium-to-large molecular systems. Since analytical second... 

Franck-Condon and Herzberg Teller Approximations of Electronic Transition AmpUtudes... 

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