FREQ Homepage

July 22, 2021


FREQ is a Python program for calculating the optimal scale factors for calculating harmonic vibrational frequencies, fundamental vibrational frequencies, and zero-point vibrational energies from electronic structure calculations. The citations are

H. S. Yu, L. J. Fiedler, I. M. Alecu, and D. G. Truhlar, Computational Thermochemistry: Automated Generation of Scale Factors for Vibrational Frequencies Calculated by Electronic Structure Model Chemistries, Computer Physics Communications 210, 132-138 (2017).


H. S. Yu, L. J. Fiedler, I. M. Alecu, S. Kanchanakungwankul, and D. G. Truhlar, FREQ - version 2 (University of Minnesota, Minneapolis, 2021).

The program utilizes a previously published scale factor optimization model presented in

"Computational Thermochemistry: Scale Factor Databases and Scale Factors for Vibrational Frequencies Obtained from Electronic Model Chemistries," I. M. Alecu, J. Zheng, Y. Zhao, and D. G. Truhlar, Journal of Chemical Theory and Computation 6, 2872-2887 (2010).

This allows one to efficiently obtain all three scale factors from a set of computed vibrational harmonic frequencies. In order to obtain the three scale factors, the user only needs to provide zero-point energies of 15 or 6 selected molecules. If the user has access to the Gaussian 09 or Gaussian 03 program, we provide the option for the user to run the program by entering the keywords for a certain method and basis set in the Gaussian 09 or Gaussian 03 program. Four other Python programs,, input6,, and, are also provided for generating Gaussian 09 or Gaussian 03 input and PBS files. The program can also be used with data from any other electronic structure package. A manual of how to use this program is included in the code package.

To obtain FREQ:

FREQ - version 2 is available for downlading from this web page (see below) under the GNU GPL v3 license.

FREQ - version 1 is available through the Computer Physics Communications Program Library at It is program FREQ by Haoyu S. Yu, Lucas J. Fiedler, I. M. Alecu, and Donald G. Truhlar. Its catalogue identifier is AFBH_v1_0.

FREQ Download:

    Manual in PDF format (222 KB)
    Program (including the manual) in tar.gz (1.6 MB)

Links to Other Pages of Interest:

This document last modified on July 22, 2021  by Software Manager