AB-INITIO INVESTIGATION OF THE N-2-HF COMPLEX - ACCURATE STRUCTURE AND ENERGETICS

Augmented correlation consistent basis sets of double (aug-cc-pVDZ), t riple (aug-cc-pVTZ), and modified quadruple zeta (aug-cc-pVQZ') qualit y have been employed to describe the N-2-HF potential energy surface a t the Hartree-Fock level and with single reference correlated wave fun ctions including Moller-Plesset perturbation theory (MP2, MP3, MP4) an d coupled cluster methods [CCSD, CCSD(T)]. The most accurate computed equilibrium binding energies D-e are cm(-1) (with counterpoise correct ion) 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 essential ly converged. Harmonic frequencies and zero-point energies were determ ined through the aug-cc-pVTZ level. Combining the zero point energies computed at the aug-cc-pVTZ level with the equilibrium binding energie s computed at the aug-cc-pVQZ' level, we predict D-0 values of 322 and 296 cm(-1), respectively, at the MP4 and CCSD(T) levels of theory. Us ing experimental anharmonic frequencies, on the other hand, the CCSD(T ) value of D-0 is increased to 415 cm(-1), in good agreement with the experimental value recently reported by Miller and co-workers, 398+/-2 cm(-1). (C) 1996 American Institute of Physics.