Electronic structure and bonding characters of the two lowest states of copper, silver, and gold monocarbides

The electronic structure and bonding characters of the two lowest states of CuC, AgC, and AuC have been systematically studied at Hartree-Fock (HF), coupled-cluster singles-doubles (CCSD), and coupled-cluster singles-doubles (triples) [CCSD(T)] levels. The ground states of CuC and AuC were assigned as (2)Pi while that of AgC assigned as (4)Sigma(-). The differences in the interactions were observed, the combined effects of relativity and electron correlation from triples excitations are crucial to the (2)Pi state of CuC and those of relativity and electron correlation are important for the (2)Pi state of AuC to be the ground state. The binding characters of the 2 Pi states of CuC, AgC, and AuC are the genuine sigma and the delocalized pi bonds and that of the (4)Sigma(-) state is the strong sigma bond. In the (2)Pi states electron correlation and relativistic effects hamper electron transfer along sigma-frame and facilitate it along pi-frame, while in the (4)Sigma(-) states electron transfer along sigma-frame is hindered by relativistic effects and the influence by electron correlation effects is slight. In addition, the variation trends of spectroscopic parameters and electronic properties of each state caused by both effects were extracted and explained. (C) 2011 Elsevier B.V. All rights reserved.