The effect of three-body forces on the vibrational frequencies of triatomic clusters

Abstract

Vibrational frequency distribution spectra for triatomic clusters were calculated using the normal-mode approximation ( T = 0 K) based on a potential-energy function comprising two- and three-body interactions. The two-body potential was represented by a Mie potential and the three-body part was approximated using the Axilrod-Teller triple-dipole equation. Calculations were performed parametrically by varying the three-body force intensity factor, Z ∗, The role of the three-body interactions on the equilibrium shapes of clusters has already been well recognized. For small Z ∗ an equilateral triangular shape is favored but, for larger Z ∗ values a linear configuration is found to be energetically more favorable. In the present parametrical analysis, it was found that the three-body forces are important also for the vibrational frequency distribution spectra. For increasing Z ∗ values, the two main vibrational peaks for the equilateral triangular configuration shift to the lower-frequency region, while the three main peaks of the linear shape shift to the higher-frequency domain. The highest shift was exhibited by the asymmetric vibrational peak for the equilateral triangular case. This work also includes a discussion for the critical case, when both the linear and the triangular shapes are equally stable energetically