Damped response theory description of two-photon absorption

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Standard two-photon absorption (TPA) calculations face challenges with large molecules and resonant states.
• Existing methods can be problematic due to high density of states or divergent expressions.

Purpose of the Study:

• To apply damped response theory for calculating TPA spectra.
• To address limitations of standard TPA calculations in complex systems.

Main Methods:

• Utilizing a modified damped cubic response function for direct TPA spectrum determination.
• Implementing exact damped response theory and its application within density functional theory.
• Employing an atomic-orbital based density matrix formulation for large systems.

Main Results:

• The damped TPA approach is suitable for selected frequency ranges and large molecules.
• It effectively handles intermediate state resonances where standard TPA expressions diverge.
• A preliminary study on R-(+)-1,1'-bi(2-naphtol) demonstrates the method's utility.

Conclusions:

• Damped response theory provides a more versatile and accurate method for TPA spectroscopy.
• The density functional theory implementation is efficient for large molecular systems.