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

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 2u state due to considerable SOC splitting in the 3 Pi 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.