The alkali metal trifluorides M+F3 −: how well can theory predict experiment?

Abstract

The alkali metal trifluorides M+ F3 − (M = Na, K, Rb, and Cs) are studied using density functional theory and traditional ab initio methods. Experimental infrared and Raman spectroscopic results suggest a pronounced change in the structure of the M+F3 − species with decreasing cation size. Stationary points are located on the M+F3 − potential energy surfaces and harmonic vibrational frequencies computed to assess how well the variou-s theoretical methods can describe this alkali metal dependence. As with the isolated F3 − anion, the theoretical results are strongly dependent on the method used, with only the B3-LYP density functional calculations reproducing correctly the structural variation inferred from the vibrational spect-ra. Additional calculations also demonstrate that this functional significantly reduces the F3 overbinding observed using B-LYP.