Complex Excited State Polarizabilities in the ADC/ISR Framework

We present the derivation and implementation of complex, frequency-dependent polarizabilities for excited states using the algebraic-diagrammatic construction for the polarization propagator (ADC) and its intermediate state representation (ISR). Based on the complex polarizability we evaluate C₆ dispersion coefficients for excited states. The methodology is implemented up to third order in perturbation theory in the Python-driven adcc toolkit for the development and application of ADC methods. We exemplify the approach using small model systems and compare it to results from coupled-cluster theory and from experiments.