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

Abstract

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 ωB97X 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 ωB97X/PBE0 vibronic transitions contributing to the final band shapes of the investigated aminocoumarin molecules.

Aiming at an accurate prediction of vibrational and electronic spectra for medium‐to‐large molecules: An overview

“…The accuracy of DFT models for the prediction of excitation energies is often performed by comparing the VE energies with experimentally observed , even though the latter depends on the band‐shape, made of vibronic transitions. For this reason, a more reliable validation can only be achieved by simulating the band‐shape from the convolution of vibronic transitions, including, where necessary, solvent and temperature effects . Figure compares the TD AH FC spectra computed using different DFT functionals, at 298K, with the experimental photoionization spectra of thiophene .…”

“…For this reason, a more reliable validation can only be achieved by simulating the band-shape from the convolution of vibronic transitions, including, where necessary, solvent and temperature effects. [191] Figure 4 compares the TD AHjFC spectra computed using different DFT functionals, at 298K, with the experimental photoionization spectra of thiophene. [89] The good match between the theoretical envelope and experimental band at about 9 eV suggests that indeed the latter is related to the 2 A 2 X 1 A 1 transition as postulated in earlier works.…”

Theoretical Simulation of the Vibrationally Resolved UV Absorption Spectrum of Acryloyl Fluoride

“…Likewise, the functional benchmarks for spectral simulations have been performed on various systems, the accuracy of the functional depends on the system significantly [30,31] and no single functional performs highly accurately for all aspects. [32,33] The chosen ωB97X-D functional is indeed shown to be effective for keto derivatives. [32] The equilibrium geometries and vibrational frequencies of the S 0 and S 1 states of acryloyl fluoride (both s-trans and s-cis isomers) were calculated by using ωB97X-D and TD ωB97X-D functional with the aug-cc-pVDZ basis set, respectively.…”

New insights into the vibrational and optical signatures of trans-stilbene via integrated experimental and quantum mechanical approaches

“…[42][43][44] All calculations have been performed in vacuum (except when explicitly stated) to be directly comparable to available experimental data and taking full account of symmetry in all computational steps. 18,28,34,48 Moreover, the first derivatives of the transition dipole moment have been included, thus going from the Franck-Condon to the Herzberg-Teller (HT) approximation. 45 In some cases bulk solvent effects (n-hexane) have been taken into account by the PCM (Polarizable Continuum Model).…”