Time-Dependent Long-Range-Corrected Density-Functional Tight-Binding Method Combined with the Polarizable Continuum...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate calculation of excited-state properties is crucial for understanding photophysical processes.
• Existing methods like time-dependent density-functional tight-binding (TD-DFTB) have limitations in accuracy.
• Long-range corrected functionals offer improved description of excited states.

Purpose of the Study:

• To develop and validate an efficient computational method for excited-state free energies and geometries.
• To assess the performance of a new time-dependent long-range corrected density-functional tight-binding method (TD-LC-DFTB2/PCM).
• To evaluate the accuracy of TD-LC-DFTB2/PCM for various molecular systems, including those with dual emission.

Main Methods:

• Implementation of a linear-response time-dependent long-range corrected density-functional tight-binding method (TD-LC-DFTB2).
• Integration with the polarizable continuum model (PCM) for solvent effects.
• Benchmark calculations on 3-hydroxyflavone and over 20 other molecules.

Main Results:

• TD-LC-DFTB2/PCM efficiently computed excited-state gradients for large systems (>1000 atoms) within 30 minutes.
• Calculated absorption and enol-form emission wavelengths for 3-hydroxyflavone agreed well with DFT and experimental data.
• The method systematically overestimated absorption and 0-0 transition energies, but showed good agreement with CAM-B3LYP.
• Adjusting the range separation parameter to 0.15 minimized deviations.

Conclusions:

• TD-LC-DFTB2/PCM is a computationally efficient method for excited-state calculations.
• The method shows potential for studying complex molecular systems, particularly in solution.
• Further refinement of the range separation parameter can improve accuracy for specific properties.