4.7 Article

Benchmarking TD-DFT against Vibrationally Resolved Absorption Spectra at Room Temperature: 7-Aminocoumarins as Test Cases

Journal

JOURNAL OF CHEMICAL THEORY AND COMPUTATION
Volume 11, Issue 11, Pages 5371-5384

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.jctc.5b00750

Keywords

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Funding

  1. Italian Ministero dell'Istruzione, dell' Universita e della Ricerca (MIUR) through Programma di Ricerca di Rilevante Interesse Nazionale (PRIN) [2010C4R8M8_002]
  2. Futuro in Ricerca (FIRB) [RBFR1248UI 002]
  3. Progettazione di Materiali Nanoeterogenei per la Conversione di Energia Solare [RBFR122HEZ]

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Time-dependent density functional theory (TD-DFT) is usually benchmarked by evaluating how the vertical excitation energies computed by using different exchange-correlation (XC) functionals compare with the maximum of the absorption spectra. However, the latter does not necessarily coincide with the vertical energies because it is affected by the vibronic band structure that has to be properly taken into account. In this work, we have evaluated the performance of several functionals belonging to different families in reproducing the vibronic structure (band shape) of four 7-aminocoumarin molecules of technological interest, whose spectra have been recorded in methylcyclohexane and acetonitrile solvents. In order to compare the computed vibronic spectra with the experimental ones in the most consistent way, the effect of temperature, often neglected, was also taken into account. We have found that no single functional provides simultaneously accurate band positions and shapes, but the combination of omega B97X vibronic couplings with PBE0 vertical energies can lead to very satisfactory results. In addition to the assessment of XC functionals, several adiabatic and vertical models proposed in the literature to compute vibrationally resolved electronic spectra have been tested and validated with respect to experiments. On these grounds, the adiabatic Hessian model has been used to perform a complete analysis of the omega B97X/PBE0 vibronic transitions contributing to the final band shapes of the investigated aminocoumarin molecules.

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