Uncertainties in Scaling Factors for ab Initio Vibrational Zero-Point Energies

Published

March 21, 2009

Author(s)

Karl K. Irikura, Russell D. Johnson III, Raghu N. Kacker, Ruediger Kessel

Abstract

Vibrational zero-point energies (ZPEs) determined from ab initio calculations are often scaled by empirical factors. An empirical scaling factor partially compensates for the effects arising from vibrational anharmonicity and incomplete treatment of electron correlation. These effects are not random, but are systematic. We report scaling factors for 30 combinations of theory and basis set, intended for predicting ZPEs from computed harmonic frequencies. An empirical scaling factor carries uncertainty. We quantify and report, for the first time, the uncertainties associated with scaling factors for ZPE. The uncertainties are larger than generally acknowledged; the scaling factors have only two significant digits. For example, the scaling factor for B3LYP/6-31G(d) is 0.9756 0.0226 (standard uncertainty). The uncertainties in the scaling factors lead to corresponding uncertainties in predicted ZPEs. The proposed method for quantifying the uncertainties associated with scaling factors is based upon the Guide to the Expression of Uncertainty in Measurement, published by the International Organization for Standardization (ISO). We also present a new reference set of 60 diatomic and 15 polyatomic experimental ZPEs that includes estimated uncertainties.

Citation

Journal of Chemical Physics

Volume

130

Issue

11

Pub Type

Journals

Keywords

ZPE, vibrations, zero-point, uncertainties, scaling factors

Citation

Irikura, K. , Johnson, R. , Kacker, R. and Kessel, R. (2009), Uncertainties in Scaling Factors for ab Initio Vibrational Zero-Point Energies, Journal of Chemical Physics (Accessed December 26, 2024)