To Predict Vibrational Spectra, Are Anharmonic Calculations Worthwhile?

Published

January 22, 2013

Author(s)

Ruth L. Jacobsen, Karl K. Irikura, Russell D. Johnson III, Raghu N. Kacker

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. 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.

Citation

Journal of Chemical Theory and Computation

Volume

9

Issue

2

Pub Type

Journals

Download Paper

https://doi.org/10.1021/ct300293a

Keywords

Harmonic frequencies, anharmonic frequencies, scaling, second-order vibrational perturbation theory, VPT2, Hartree-Fock, second-order perturbation theory, density functional theory, HF, MP2, DFT, B3LYP, quantum chemistry

Citation

Jacobsen, R. , Irikura, K. , Johnson, R. and Kacker, R. (2013), To Predict Vibrational Spectra, Are Anharmonic Calculations Worthwhile?, Journal of Chemical Theory and Computation, [online], https://doi.org/10.1021/ct300293a (Accessed October 1, 2025)