The treacherous potential energy hypersurface of AgSiO

Abstract

The AgSiO system has been a source of puzzlement for more than a decade, with experimental and theoretical studies providing bewildering conclusions regarding the structure of the molecule. State-of-the-art coupled cluster and multireference configuration interaction methods have been applied in the present work, in conjunction with techniques designed to incorporate relativistic effects. With the coupled cluster single and double excitation with perturbatively applied triples method [CCSD(T)], the Ag–SiO dissociation energy is predicted to be 6.8 kcal/mole, with the equilibrium structure being a nearly isosceles triangle. However, a second minimum Ag–O–Si structure with bond angle ∼150° lies at less than 1 kcal/mole. With the multireference CI approach (up to 48 million configurations) the energetic order of these two minima is reversed. In contrast, both second-order perturbation theory and density functional theory predict an Ag–Si–O structure with bond angle ∼115° to be the global minimum. The present theoretical results represent a major step forward. However, it is clear that AgSiO will be the subject of experimental and theoretical studies for some time to come.