New methods for calculations of complex potential energy surfaces and spectroscopic characteristics of electronic resonances

Electronic resonances are non-stationary quantum states of atoms or molecules which can spontaneously decay by the emission of an electron. They are characterized by a finite lifetime that determines their chemical reactivity and spectroscopic signature. Resonances are embedded in the continuum of many-body unbound states, where standard computational methods of quantum chemistry are not applicable. Therefore, theoretical modeling of resonances is highly challenging even for the smallest molecules. There are not yet ab initio techniques that would allow to model resonance states with similar accuracy and control as it is now possible for stationary, bound states. Taking autoionization into account remains one of the biggest challenges in electronic structure calculations.

The main objective of this project is to develop a new theoretical methodology to study electronic resonances, with particular focus on efficient calculations of complex potential energy surfaces. The approach we propose is based on Fano-Feshbach formalism and equation-of-motion coupled-cluster (EOM-CC) method. EOM-CC states will be augmented with a genuine continuum orbital, computed with a grid-based discrete variable representation method (DVR) and single-center partial-wave expansion. To broaden the applicability of our approach, we will implement and test several techniques for correct identification of a resonant state within the proposed computational protocol. The developed methodology will be applied in the calculations of complex potential energy surfaces in order to investigate quantum dynamics of processes such as Penning ionization or photo-fragmentation triggered by XUV or X-ray photons. In parallel, we will implement a variant of Multichannel Schwinger Variational Method based on the EOM-CC vectors used to expand short-range many-body scattering wave function. This will be a pioneering application of the EOM-CC technique to the problem of electron-molecule scattering.