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

TL;DR

This paper introduces a TD-DFTB method for calculating vibrationally resolved UV/Vis spectra, incorporating nuclear vibrations via the AH|FC approach, and demonstrates its accuracy against TD-DFT benchmarks.

Contribution

The paper develops a novel TD-DFTB scheme for vibrationally resolved UV/Vis spectra that explicitly includes nuclear vibrational effects using the AH|FC method.

Findings

Achieves very good agreement with TD-DFT calculations.

Successfully benchmarks the method on aromatic and polar molecules.

Utilizes the 3ob:freq parameter set for accurate results.

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.