| Abstract [eng] |
Wavepacket Dynamics of Coupled Molecules Interacting with Anharmonic Vibrations Various approaches exist when describing the nature of light induced excitations in the photosynthetic complexes. There is still the discussion how the electronic excitations appear and behave in such environments. However, it is concluded that molecular vibrations and thermal environment plays the crucial role in the behavior of excitation dynamics. In cases of strong interaction between the exciton and molecular vibrations the polaronic effects may be detected as the lattice of the molecular structure becomes strongly deformed and exciton becomes self-trapped in formed potential well. It is also well known that molecular vibrations are anharmonic in natural systems and effects of such vibrations are detectable in the low-temperature spectroscopy experiments of excited photosynthetic complexes. Multitude of theoretical methods have been developed to describe complex nature of polaronic excitation dynamics in photosynthetic molecular aggregates. In this work we apply the time dependent variational method, which allows us to describe the coorelated evolution of the vibrational modes and excitonic amplitudes. Variational method has been widely studied using different trial functions and Hamiltonians, however there were a lack of applications analyzing dynamics of anharmonic vibrations coupled with electronic excitation. In this work we propose the modified Davydov Ansatz, which includes squeezed coherent states and thus allows for more accurate description of wavepackets oscillations in phase space. As the Morse potential is well known anharmonic potential and widely used in the spectroscopy, we apply it to model the environmental oscillators of the system. We conclude that our equations reveal the shift of the lowest energy state of Morse oscillators in comparison with harmonic oscillators. The modified Davydov Ansatz leads to much more stable formation of excitonic polarons. If the squeezed coherent states are taken into account the vibrational bound and unbound states of Morse oscillators can be observed in the absorption spectra. |
