Efficient implementation of isotropic cubic response functions for two-photon absorption cross sections within the...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Spectroscopy

Background:

• Accurate calculation of molecular properties like two-photon absorption (TPA) cross sections is crucial for materials science and drug discovery.
• Existing methods for calculating TPA often require significant computational resources, limiting their application to larger systems.

Purpose of the Study:

• To develop computationally efficient expressions for isotropic second-order hyperpolarizability within the self-consistent field approximation.
• To implement these expressions for calculating TPA cross sections, reducing computational cost.

Main Methods:

• Derivation of computationally tractable expressions for isotropic second-order hyperpolarizability.
• Development of a novel tensor average formulation for evaluating isotropic damped cubic response functions.
• Implementation and application to molecular systems including alanine-tryptophan and organic molecules.

Main Results:

• The tensor average formulation requires substantially fewer auxiliary Fock matrices compared to explicit tensor component calculation (∼3.3% in off-resonance, ∼10% in resonance regions).
• Numerical examples for TPA cross sections demonstrate the method's applicability.
• Reduced and approximate forms of the cubic response function show a relative error of less than ∼5% compared to the full form.

Conclusions:

• The developed method provides a computationally efficient and accurate approach for calculating two-photon absorption cross sections.
• This advancement can enable the study of larger and more complex molecular systems.
• The findings offer a valuable tool for researchers in computational chemistry and related fields.