Complex excited state polarizabilities in the ADC/ISR framework.

Area of Science:

• Quantum Chemistry
• Computational Physics
• Spectroscopy

Background:

• Accurate calculation of molecular properties is essential for understanding chemical and physical phenomena.
• Excited state properties, such as polarizability, are challenging to compute accurately.
• Dispersion coefficients (C6) are vital for describing van der Waals interactions.

Purpose of the Study:

• To derive and implement a method for calculating complex, frequency-dependent polarizabilities for excited states.
• To evaluate C6 dispersion coefficients for excited states using the developed polarizability method.
• To provide a robust computational tool for excited-state property calculations.

Main Methods:

• Utilized the algebraic-diagrammatic construction (ADC) for the polarization propagator.
• Employed the intermediate state representation within the ADC framework.
• Implemented the methodology up to third order in perturbation theory.
• Developed the 'adcc' Python toolkit for ADC calculations.

Main Results:

• Successfully derived and implemented complex, frequency-dependent polarizabilities for excited states.
• Calculated C6 dispersion coefficients for excited states based on the computed polarizabilities.
• Demonstrated the approach using model systems and validated against other ab initio methods and experimental data.

Conclusions:

• The developed ADC-based method provides accurate complex polarizabilities and C6 coefficients for excited states.
• The 'adcc' toolkit offers a versatile platform for advanced quantum chemical calculations.
• This work advances the computational study of excited-state molecular properties and intermolecular forces.