(Non-) periodic variation of excited-state properties for coinage metal dimers M2 (M = Cu, Ag, Au, Rg)

Abstract

The impact of relativistic effects on the periodicity of elements has significant implications for the prediction of the properties of atoms and their compounds. In this study, (non-) periodic variations of the properties of Group IB dimers are investigated from the perspective of excited states. The EOM-CCSD and EOM-CCSD(T)(a)* methods along with wave function analysis tools are employed to investigate their excited state. According to our results, the EOM-CCSD(T)(a)* approach with the QZ basis set is required to obtain reasonable results for some states. SOC plays a crucial role in the excited state properties of Au₂ and Rg₂, and our results show that the ground state of Rg₂ is an open-shell 2_u state due to considerable SOC splitting in the ³Π state. To rationalize (non-) periodic variations of excited states, ionization potentials and electron affinities of these molecules are obtained to approximate the energies of occupied and virtual orbitals. Low-lying excited states are mainly transitions from occupied orbitals to the LUMO orbital for Cu₂, Au₂, and Rg₂, while they are transitions from the HOMO to virtual orbitals in Ag₂. This is due to a large energy difference between the HOMO and HOMO−1 in Ag₂. The excited state properties of Au₂ are similar to those of Cu₂ when SOC is not considered due to scalar relativistic effects. The excited state properties of Rg₂ differ from other molecules in the same group, as its LUMO orbital is predominantly composed of d orbitals, while they are primarily s orbitals in the other molecules.