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

Area of Science:

• Computational Chemistry
• Spectroscopy
• Quantum Chemistry

Background:

• Accurate calculation of UV/Vis spectra is crucial for understanding molecular electronic transitions.
• Existing methods like time-dependent density functional theory (TD-DFT) can be computationally expensive.
• Incorporating nuclear vibrations significantly enhances spectral accuracy but adds complexity.

Purpose of the Study:

• To develop and validate a computationally efficient time-dependent density functional based tight-binding (TD-DFTB) scheme.
• To explicitly include nuclear vibrational effects in the calculation of UV/Vis spectra.
• To benchmark the new TD-DFTB method against TD-DFT for accuracy.

Main Methods:

• Development of a TD-DFTB scheme incorporating nuclear vibrations.
• Application of the adiabatic Hessian Franck-Condon method with harmonic nuclear wavefunctions.
• Benchmarking against TD-DFT for strongly dipole-allowed excitations in aromatic and polar molecules.

Main Results:

• The TD-DFTB scheme successfully calculates UV/Vis spectra, accounting for nuclear vibrational effects.
• The method demonstrates very good agreement with TD-DFT results when using the 3ob:freq parameter set.
• The computational efficiency of TD-DFTB offers a viable alternative for spectral calculations.

Conclusions:

• The developed TD-DFTB method provides an accurate and efficient approach for computing vibrationally resolved UV/Vis spectra.
• This method serves as a valuable tool for molecular electronic structure and spectroscopy studies.
• The findings suggest TD-DFTB can be a practical alternative to TD-DFT for specific spectroscopic applications.