Ab initio investigation of the N₂-HF complex: Accurate structure and energetics

Augmented correlation consistent basis sets of double (aug-cc-pVDZ), triple (aug-cc-pVTZ), and modified quadruple zeta (aug-cc-pVQZ′) quality have been employed to describe the N₂-HF potential energy surface at the Hartree-Fock level and with single reference correlated wave functions including Møller-Plesset perturbation theory (MP2, MP3, MP4) and coupled cluster methods [CCSD, CCSD(T)]. The most accurate computed equilibrium binding energies D_e are (with counterpoise correction) 810 cm^-1 (MP4/aug-cc-pVQZ′) and 788 cm^-1 [CCSD(T)/aug-cc-pVQZ′]. Estimated complete basis set limits of 814 cm^-1 (MP4) and 793 cm^-1 [CCSD(T)] indicate that the large basis set results are essentially converged. Harmonic frequencies and zero-point energies were determined through the aug-cc-pVTZ level. Combining the zero point energies computed at the aug-cc-pVTZ level with the equilibrium binding energies computed at the aug-cc-pVQZ′ level, we predict D₀ values of 322 and 296 cm^-1, respectively, at the MP4 and CCSD(T) levels of theory. Using experimental anharmonic frequencies, on the other hand, the CCSD(T) value of D₀ is increased to 415 cm^-1, in good agreement with the experimental value recently reported by Miller and co-workers, 398±2 cm^-1.