title: Anharmonic Vibrational Frequency Calculations Are Not Worthwhile for Small Basis Sets.
abstract: Anharmonic calculations using vibrational perturbation theory are known to provide near-spectroscopic accuracy when combined with high-level ab initio potential energy functions. However, performance with economical, popular electronic structure methods is less well characterized. We compare the accuracy of harmonic and anharmonic predictions from Hartree-Fock, second-order perturbation, and density functional theories combined with 6-31G(d) and 6-31+G(d,p) basis sets. As expected, anharmonic frequencies are closer than harmonic frequencies to experimental fundamentals. However, common practice is to correct harmonic predictions using multiplicative scaling. The surprising conclusion is that scaled anharmonic calculations are no more accurate than scaled harmonic calculations for the basis sets we used. The data used are from the Computational Chemistry Comparison and Benchmark Database (CCCBDB), maintained by the National Institute of Standards and Technology, which includes more than 3939 independent vibrations for 358 molecules.
authors.affiliation: Chemical and Biochemical Reference Data Division and ‡Applied and Computational Mathematics Division, National Institute of Standards and Technology , Gaithersburg, Maryland 20899-8320, United States.
authors.forename: Ruth L
authors.initials: RL
authors.lastname: Jacobsen
authors.affiliation: Chemical and Biochemical Reference Data Division and ‡Applied and Computational Mathematics Division, National Institute of Standards and Technology , Gaithersburg, Maryland 20899-8320, United States.
authors.forename: Russell D
authors.initials: RD
authors.lastname: Johnson
authors.affiliation: Chemical and Biochemical Reference Data Division and ‡Applied and Computational Mathematics Division, National Institute of Standards and Technology , Gaithersburg, Maryland 20899-8320, United States.
authors.forename: Karl K
authors.initials: KK
authors.lastname: Irikura
authors.affiliation: Chemical and Biochemical Reference Data Division and ‡Applied and Computational Mathematics Division, National Institute of Standards and Technology , Gaithersburg, Maryland 20899-8320, United States.
authors.forename: Raghu N
authors.initials: RN
authors.lastname: Kacker