Ground state potential energy surfaces and bound states of M-He dimers (M=Cu,Ag,Au): A theoretical investigation

Abstract

We present an ab initio investigation on the ground state interaction potentials [potential energy surface (PES)] between helium and the group 11 metal atoms: copper, silver, and gold. To the best of our knowledge, there are no previous theoretical PESs proposed for Cu-He and Au-He, and a single one for Ag-He [Z. J. Jakubek and M. Takami, Chem. Phys. Lett. 265, 653 (1997)], computed about 10 years ago at MP2 level and significantly improved by our study. To reach a high degree of accuracy in the deteRmination of the three M-He potentials (M=Cu,Ag,Au), we performed extensive series of test computations to establish the appropriate basis set, the theoretical method, and the computational scheme for these systems. For each M-He dimer we computed the PES at the CCSD(T) level of theory, starting from the reference unrestricted Hartree-Fock wave function. We described the inner shells with relativistic small core pseudopotentials, and we adopted high quality basis sets for the valence electrons. We also performed CCSDT computations in a limited set of M-He internuclear distances, adopting a medium-sized basis set, such as to define for each dimer a CCSD(T) to CCSDT correction term and to improve further the quality of the CCSD(T) interaction potentials. The Cu-He complex has minimum interaction energy (Emin) of -28.4 μhartree at the internuclear distance of 4.59 Å (Rmin), and the short-range repulsive wall starts at 4.04 Å (RE=0). Quite interestingly, the PES of Ag-He is more attractive (Emin =-33.8 μhartree) but presents nearly the same Rmin and RE=0 values, 4.60 and 4.04 Å, respectively. The interaction potential for Au-He is markedly deeper and shifted at shorter distances as compared to the lighter complexes, with Emin =-69.6 μhartree, Rmin =4.09 Å and RE=0 =3.60 Å. As a first insight in the structure of M- Hen aggregates, we deteR mined the rovibrational structure of the three M-He dimers. The Cu-He and Ag-He potentials support just few rotational excitations, while the Au-He PES admits also a bound vibrational excitation. © 2008 American Institute of Physics.