RT-EOM-CCSD Inner and Outer Valence Ionization Energies

Photoelectron spectroscopy (PES), from the UV to X-rays, is a fundamental experimental method for the characterization of materials ranging from adsorbed molecules to catalysts to metals in solution. Despite this broad applicability, the analysis of PES is often hampered by its reliance on the use of standard materials. Therefore, to facilitate the study of unknown systems, advanced theoretical methods for the simulation of PES are highly desirable. In this talk we present the successful deployement of the real-time equation-of-motion coupled cluster singles and doubles (RT-EOM-CCSD) approach[1] to the calculation of the inner and outer valence PES, extending the method's original target of core level spectra to the full spectrum. We show calculations for a series of small molecules which yield ionization energies and total spectral functions that are in good agreement with experiment and of comparable quality (±0.2 eV) to CI-based methods, even for modestly sized basis set. In particular RT-EOM-CCSD provides results that compare well with experiment for inner valence ionizations where correlation is important.

[1] "Real-Time Equation-of-Motion CCSD Cumulant Green's Function", FD Vila et al., J. Chem. Theory Comput. (doi:10.1021/acs.jctc.1c01179).