Vibrationally resolved UV/Vis spectroscopy with time-dependent density functional based tight binding

Abstract

We report a time-dependent density functional based tight-binding (TD-DFTB) scheme for the calculation of UV/Vis spectra, explicitly taking into account the excitation of nuclear vibrations via the adiabatic Hessian Franck-Condon (AH|FC) method with a harmonic approximation for the nuclear wavefunction. The theory of vibrationally resolved UV/Vis spectroscopy is first summarized from the viewpoint of TD-DFTB. The method is benchmarked against time-dependent density functional theory (TD-DFT) calculations for strongly dipole allowed excitations in various aromatic and polar molecules. Using the recent 3ob:freq parameter set of Elstner's group, very good agreement with TD-DFT calculations using local functionals was achieved.

Accurate prediction of vertical electronic transitions of Ni(II) coordination compounds via time dependent density functional theory

“…It must be highlighted that TD‐DFT electronic vertical excitation energies have been computed using the PCM implicit solvation model within the Linear Response Non‐Equilibrium framework (LRNE) . Considering that some authors have recently shown that this is not necessarily the best approximation, a Franck‐Condon analysis was performed to calculate the vibrational components of the spectrum of [Ni(H ‐2 GGC)] 2– according to the procedure established by Barone et al g] [ ] The Franck‐Condon factor , less than 10 −4 , indicates that this method is not applicable for our species because the geometry of the excited state—which shows a not negligible deviation from the planarity—is different with respect to that of the ground state. In particular, the dihedral angles θ and φ involving, respectively, the terminal nitrogen and sulfur donors increase from −6.2 to 14.9° (θ) and from −1.5 to 2.3° (φ); the superimposition of the ground and excited state structures is shown in Figure S1 of Supporting Information, while the Cartesian coordinates, the electronic and zero‐point vibrational energy (ZPVE), and the values for the adiabatic and 0‐0 excitations (Δ E adiabatic and Δ E 0‐0 ) are reported in Supporting Information Tables S6 and S7.…”

Density-functional tight-binding: basic concepts and applications to molecules and clusters

“…Absorption spectra were computed for neutral polyacenes ranging in size from naphthalene to heptacene and compared with experimental as well as TD-DFT data. Vibrationally resolved UV/Vis spectra of various aromatic and polar molecules were calculated using TD-DFTB excitation energies and analytical gradients in ref [137]. The results of TD-DFTB were found in a very good agreement with the TD-DFT calculations using local functionals.…”

“…The derivation relies on the so-called Z-vector method, which was initially introduced by Furche and Ahlrichs [187,188] to compute analytical forces for the TD-DFT excited states. The procedure was further used to derive TD-DFTB gradients by Heringer et al [189,190] and led to the final expression published in ref [137].…”

Non-adiabatic molecular dynamics investigation of the size dependence of the electronic relaxation in polyacenes

“…[34] In the present work, we report a new implementation of the trajectory surface hopping dynamics coupled to the TD-DFTB approach within the deMon-Nano code [35] and present its first application devoted to PAHs. More precisely, we investigate the dynamical evolution of electronically-excited polyacenes ranging from naphthalene to heptacene, which are systems of choice as they are known to present a closed-shell GS electronic configuration [36,37] and their absorption spectra have been shown to be well described both at the TD-DFT [38] and the TD-DFTB [12,36] levels of theory. The non-adiabatic dynamics of polyacenes following the absorption of a photon in their brightest absorption band is investigated (i) determining the typical timescales of relaxation, (ii) performing analysis in terms of level crossings and evolution with size as well as (iii) estimating the transfer of the electronic energy towards vibrational modes.…”