Analytic nuclear gradients of the algebraic-diagrammatic construction scheme for the polarization propagator up to third order of perturbation theory.

Analytic gradient expressions for the algebraic diagrammatic construction (ADC) scheme for the polarization propagator up to third order are derived using a Lagrangian approach. An implementation within the Q-CHEM electronic structure package for excited-state nuclear gradients of the ADC(2), ADC(2)-x, and ADC(3) models based on restricted and unrestricted Hartree-Fock references is presented. Details of the implementation and the applicability of the newly derived gradients for geometry optimizations and the quality of the resulting structures are discussed.