Vibronic-structure tracking: A shortcut for vibrationally resolved UV/Vis-spectra calculations

Abstract

The vibrational coarse structure and the band shapes of electronic absorption spectra are often dominated by just a few molecular vibrations. By contrast, the simulation of the vibronic structure even in the simplest theoretical models usually requires the calculation of the entire set of normal modes of vibration. Here, we exploit the idea of the mode-tracking protocol [M. Reiher and J. Neugebauer, J. Chem. Phys. 118, 1634 (2003)] in order to directly target and selectively calculate those normal modes which have the largest effect on the vibronic band shape for a certain electronic excitation. This is achieved by defining a criterion for the importance of a normal mode to the vibrational progressions in the absorption band within the so-called "independent mode, displaced harmonic oscillator" (IMDHO) model. We use this approach for a vibronic-structure investigation for several small test molecules as well as for a comparison of the vibronic absorption spectra of a truncated chlorophyll a model and the full chlorophyll a molecule. We show that the method allows to go beyond the often-used strategy to simulate absorption spectra based on broadened vertical excitation peaks with just a minimum of computational effort, which in case of chlorophyll a corresponds to about 10% of the cost for a full simulation within the IMDHO approach.

Structures, Spectroscopic Properties, and Dioxygen Reactivity of 5- and 6-Coordinate Nonheme Iron(II) Complexes: A Combined Enzyme/Model Study of Thiol Dioxygenases

“…These were all paired with an Ahlrichs def2 family triple- ξ basis set (def2-TZVP). 44–45 With the exception of PBE0, all functionals produced satisfactory results when compared to experimental data (Figure S3). However, in the region of interest, experimental features were best reproduced using the CAM-B3LYP range-separated functional.…”

On the origin of the shift between vertical excitation and band maximum in molecular photoabsorption

“…In the computational analysis of UV/Vis photoabsorption spectra of molecules, several authors have noticed that the band maximum E max i and the vertical excitation E v i of band i, computed at the same electronic structure level, are shifted by up to 0.2 eV, with the band maximum systematically redshifted [1][2][3][4][5]. This shift δ i (Fig.…”

“…In the last years, diverse methods for first-principle spectrum simulations have been proposed [5][6][7][8][9][10], leading to high accurate predictions of band shapes, including their vibrational resolution [11]. Through simulations of vibrationally resolved absorption spectra of several molecules, Avila Ferrer et al [3] confirmed the existence of the redshift and suggested to compare vertical excitations not to the band maximum but to the first moment M 1 (center of gravity) of the absorption band.…”

Evaluating 0–0 Energies with Theoretical Tools: A Short Review

“…We do not intend to provide an exhaustive list of the works considering only one or two compounds and their comparison with experiment, or a specific chemical family of compounds. For the second category, the interested reader can find several works devoted to, e. g., fluoroborate derivatives, biological chromophores, DNA bases, cyanines, coumarins, as well as many other works focussed on band shapes rather than energies …”