Implementation of analytical excited state gradients for open-shell systems in time-dependent density functional...

Area of Science:

• Computational chemistry
• Quantum chemistry
• Photochemistry

Background:

• Excited state potential energy surfaces are crucial for understanding molecular photochemistry and photophysics.
• Calculating excited state gradients is essential for studying reaction dynamics and molecular behavior.
• Standard time-dependent density functional theory (TDDFT) provides accurate excited state energies but has high computational costs.

Purpose of the Study:

• To extend the time-dependent density functional theory plus tight binding (TDDFT+TB) method for calculating analytical excited state gradients to open-shell molecular systems.
• To improve the computational efficiency of calculating excited state properties for open-shell molecules.

Main Methods:

• Implementation of unrestricted TDDFT+TB analytical gradients within the Amsterdam Density Functional engine.
• Adaptation of existing closed-shell gradient code by modifying the coupling matrix and incorporating spin indices for open-shell systems.
• Validation through comparative calculations on various molecular systems.

Main Results:

• The developed unrestricted TDDFT+TB method provides accurate excited state gradients for open-shell molecules.
• The method demonstrates comparable accuracy to standard TDDFT but with significantly improved computational efficiency.
• Emission energies and gradient accuracy were validated against established methods.

Conclusions:

• The unrestricted TDDFT+TB method is a reliable and efficient tool for studying the excited state properties of open-shell molecular systems.
• This advancement reduces the computational burden for photochemical and photophysical investigations.
• The findings facilitate more accessible and extensive research into excited state dynamics.