Abstract

Electronic resonances are metastable atomic or molecular systems that can decay by electron detachment. They play an important role in biological processes such as DNA fragmentation induced by slow electrons or in interstellar reactions as in the formation of neutral molecules and molecular anions. As opposed to bound states, resonances do not correspond to discrete eigenstates of a Hermitian Hamiltonian, and therefore their theoretical description requires special methods. The complex absorbing potential (CAP) method can be used to calculate both the energy and the lifetime of a resonance as a discrete eigenstate in a non-Hermitian time-independent framework. The CAP method allows for applying well-known bound-state electronic structure methods to resonances as well. In this work, the applicability of CAP-augmented equation-of-motion coupled-cluster (CAP-EOM-CC) methods is extended for locating equilibrium structures and crossings on complex-valued potential energy surfaces of electronic resonances by introducing analytic energy gradients. The structure and energy of these points are needed for, e.g., estimating the importance of a specific dissociation route or deactivation process. The accuracy of structural parameters, vertical and adiabatic electron affinities, and resonance widths obtained with approximate methods and various diffuse basis sets is investigated. Applications of optimization methods are also presented for systems that are relevant in interstellar or biological processes. Properties of the complex-valued potential energy surfaces of anionic resonances of acrylonitrile and methacrylonitrile are connected to experimental observations. Dissociative electron attachment to chlorosubstituted ethylenes is also investigated. This can help in understanding detoxification processes of these compounds and might facilitate the exploration of DEA pathways for other halogenated molecules as well.