CC-R12 calculations on the lowest stationary points of the H5+ energy surface

Abstract

The four stationary points lowest in energy on the H₅⁺ potential energy surface are studied at various levels of sophistication including CCSD(T)-R12 calculations. Absolute energies are obtained with errors less than 0.5 kJ mol⁻¹. Relative energies are supposed to be much more accurate. The binding energy (D₀) of H₅⁺ with respect to H₃⁺ and H₂ is 35.9±0.1 kJ mol⁻¹. The D_2d structure is a saddle point only ∽0.8 kJ mol⁻¹ above two equivalent minima of C_2v symmetry.