Nieuwe varianten van de tweede-orde benaderende gekoppelde-clustermethode met enkelvoudige en tweevoudige excitaties

Electronic resonances are metastable states embedded in the ionization or detachment continuum. They play a central role in many processes in which electrons become unbound, but are beyond the reach of standard quantum chemical methods. An elegant treatment of electronic resonances is possible in terms of complex-valued energies. So far, such approaches have been combined only with high-level electronic structure methods and applied to small molecules with max. 10-15 atoms. The goal of this work is to develop methods suitable for the investigation of electronic resonances in larger molecules. For this purpose, second-order approximate coupled-cluster (CC2) theory will be combined with complex-energy approaches and implemented into the Q-Chem program package. The resulting suite of methods will include approaches for the ground electronic state as well as for electronically excited, ionized, and electron-attached states.