Real-time equation-of-motion CC cumulant and CC Green's function simulations of photoemission spectra of water and water dimer

TL;DR

This paper presents real-time equation-of-motion CC cumulant and Green's function methods for simulating photoemission spectra of water and water dimer, showing high accuracy and detailed spectral features.

Contribution

It introduces and applies RT-EOM-CC and CCGF methods to molecular photoemission spectra, demonstrating their accuracy and analyzing spectral features and basis set effects.

Findings

Methods agree well with each other and experiment.

Ionization potentials are accurate within 0.1 eV.

Spectral features depend on molecular geometry and basis set choice.

Abstract

Newly developed coupled-cluster (CC) methods enable simulations of ionization potentials and spectral functions of molecular systems in a wide range of energy scales ranging from core-binding to valence. This paper discusses results obtained with the real-time equation-of-motion CC cumulant approach (RT-EOM-CC), and CC Green's function (CCGF) approaches in applications to the water and water dimer molecules. We compare the ionization potentials obtained with these methods for the valence region with the results obtained with the CCSD(T) formulation as a difference of energies for N and N-1 electron systems. All methods show good agreement with each other. They also agree well with experiment, with errors usually below 0.1 eV for the ionization potentials. We also analyze unique features of the spectral functions, associated with the position of satellite peaks, obtained with the RT-EOM-CC and CCGF methods employing single and double excitations, as a function of the monomer OH bond length and the proton transfer coordinate in the dimer. Finally, we analyze the impact of the basis set effects on the quality of calculated ionization potentials and find that the basis set effects are less pronounced for the augmented-type sets.