Theoretical investigation of copper clusters using the electron propagator theory

Different decouplings of the Electron Propagator Theory (EPT) have been applied to many organic/inorganic compounds to get their vertical ionization potentials, while its potential in metal clusters is yet to be explored. In this study, we focus on assessing the reliability of this method for copper clusters, Cu_n (n = 1-13), as a case study. Furthermore, the wave function methods such as Hartree-Fock theory, Moller-Plesset perturbation theory, coupled-cluster theory, and long-range corrected density functional theory (LC-DFT) methods were also employed using the direct method (orbital eigenvalues) and indirect methods for comparison. The results show that outer-valance green function (OVGF) decoupling of the EPT methods gives a mean signed error (MSE) of 0.14 eV for the vertical ionization energies, which are lowest followed by partial third-order (P3) and modified partial third-order (P3+) methods. We presumed that the predicted vertical electron affinity using the EPT methods would be helpful for the experimentalists in the coming years. Therefore, electron propagator theory is reliable and should be explored extensively to get vertical ionization potentials and vertical electron affinities of other precious and non-precious metal clusters.

Graphical abstract

Different decouplings of the Electron Propagator Theory (EPT) have been applied to many organic/inorganic compounds to get their vertical ionization potentials, while its potential in metal clusters is yet to be explored. In this study, we focus on assessing the reliability of this method for copper clusters as a case study. It was found that the EPT is reliable, and this study encourages exploration of its untapped potential in other transition metal clusters.