A new twist on quasi-classical approaches to vibronic spectra

In continuation of our efforts for the description of nuclear vibrational effects in X-ray (or in general in vibronic) spectra, we have recently published an article:

Sven3

 

With this publication we tried to resolve the deficiency of the previously suggested method: while talking about transitions between several electronic states, the actual dynamics follows the ground state potential only. Here, making use of the expertise of Sven Karsten and Sergei Ivanov, we employ imaginary-time path integral technique to formulate a method accounting for the dynamics on multiple potential energy surfaces.
In principle, the quasi-classical approaches to the dynamics in the electronic ground state are well established. They employ the so-called Kubo-transformed time correlation functions. Kubo form is beloved by physicists due to its convenient symmetry properties making it the most classical-like quantum correlation function. In our article, we raised a question whether Kubo correlation function stays the most optimal choice when electronic transitions come into play? The answer is – not really.
If you criticize – suggest a better choice. That is why we introduce a generalized quantum time correlation function. It contains many well-established variants, including the Kubo one, as particular cases. But most importantly, it also provides a way to construct a family of new quantum correlation functions.  On the example of a 1D anharmonic model, we have shown that the new approaches may lead to superior results. This generalized strategy paves the way to seek for the even more optimal formulations.

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