Assessment of various density functionals and basis sets for the calculation of molecular anharmonic force fields

in a previous contribution, we established the suitability of density functional theory (I)FT) for the calculation of molecular anharmonic force fields. In the present work, we have assessed a wide variety of basis sets and exchange-correlation functionals for harmonic and fundamental frequencies, equilibrium, and ground-state rotational constants, and thermodynamic functions beyond the rigid rotor-harmonic oscillator (RRHO) approximation. The fairly good performance of double-zeta plus polarization basis sets for frequencies results from an error compensation between basis set incompleteness and the intrinsic error of exchange-correlation functionals. Triple-zeta plus polarization basis sets are recommended, with an additional high-exponent d function on second-row atoms. All conventional hybrid generalized gradient approximation (GGA) functionals; perform about equally well: high-exchange hybrid GGA and meta-GGA functionals designed for kinetics yield poor results, with the exception of of the very recently developed BMK functional, which takes a middle position along with the HCTH/407 (second-generation GGA) and TPSS (meta-GGA) functionals. Second-order Moller-Plesset perturbation theory (MP2) performs similarly to these functionals but is inferior to hybrid GGAs such as B3LYP and B97-1. (c) 2005 Wiley Periodicals, Inc.