The efficient use of renewable energies represent an important technological challenge. In order to tackle it, various strategies have been proposed and studied. Some of them, like luminescent solar concentrators, relies on the absorption and emission capabilities of organic chromophores, whose efficiency depends on the importance of the Stokes shift to minimize the risk of self-absorption. Because of the large number of potential candidates, computational chemistry represents a very interesting tool to predict and understand the efficiency of a series of chromophores. In this context, the simulation of vibrationally resolved electronic spectra provides a more accurate description of the absorption and emission maxima.<br/>However, those systems are often flexible and undergo significant changes upon the electronic excitation, which are poorly described by most theoretical models, based on the harmonic approximation. An effective solution is to use block-based approaches, where large-amplitude motions are treated separately by an ad-hoc procedure, whereas the other modes are treated at the harmonic level. Since for those models the coupling between different blocks is neglected, the coordinate system, used in the simulation must be chosen carefully in order to minimize those coupling terms. Regarding this matter, Cartesian coordinates are generally unsatisfactory, and internal coordinates are better suited. A significant drawback, however, is the selection of non-redundant coordinates.<br/>In this contribution, different fully-automatized algorithms for the generation of natural internal coordinates, supporting also large-size systems with complex topologies, will be presented. Based on the use of those coordinate systems, a block-based approach will be presented, where the potential energy surface along the large-amplitude motion is obtained after an explicit, whereas the vibrational wavefunctions are computed using a DVR-based approach.<br/>This theoretical framework will be applied to the simulation of vibronic spectra, both at the time-independent (TI) and at the time-dependent (TD) level, of flexible systems, where a single degreee of freedom is treated using the DVR approach. The further extension to the treatment of more complex systems, where multiple flexible degrees of freedom are present, will be discussed.

Computational tools for the simulation of vibronic spectra of flexible systems

251st National Meeting (2016)

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