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.