PIPFit Homepage

Date of this version of the software: Feb. 11, 2022

Most recent update of manual: Feb. 13, 2022

Most recet update of this Web page: Feb. 11, 2022

PIPFit 2022

Ke R. Yang, Zoltan Varga, Kelsey A. Parker, Yinan Shu, and Donald G. Truhlar
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455-0431, USA


The PIPFit 2022 program can be used to develop analytic representations of  potential energy surfaces for three-body and four-body systems. A weighted least-squares fit is performed with permutationally invariant polynomials (PIPs) whose variables are Morse-like bond functions, Gaussians, mixed exponential–Gaussians (MEGs), or hyperbolic secant variables. Three kinds of fit can be performed with the program:

o   PIPs fit to the whole potential, as originally proposed by Braams, Bowman, and Xie,

o   connected PIPs fit to the whole potential after removing the unconnected terms,

o   connected PIPs fit to the many-body part of the  potential after removing the unconnected terms and the two-body terms.

The program can also perform a two-stage fit in which one first fits lower-level energetic data with a large number of geometries and then fits higher-level corrections with a smaller set of geometries.

PIPFit 2022 Users Manual:

PDF format


Citation for the program:

Yang, Ke R; Varga, Zoltan; Parker, Kelsey A; Shu, Yinan; Truhlar, Donald G. (2022).   PIPFit 2022. Retrieved from the Data Repository for the University of Minnesota, https://doi.org/10.13020/tnzc-nt34.


Selected citations for methods and applications:

"Global Ab Initio Ground-State Potential Energy Surface of N4," Y. Paukku, K. R. Yang, Z. Varga, and D. G. Truhlar, Journal of Chemical Physics 139, 044309/1-8 (2013). doi.org/10.1063/1.4811653.

Erratum: 140, 019903 (2014).


"An Improved Potential Energy Surface and Multi-Temperature Quasiclassical Trajectory Calculations of N2 + N2 Dissociation Reactions," J. Bender, P. Valentini, I. Nompelis, Y. Paukku, Z. Varga, D. G. Truhlar, T. Schwartzentruber, and G. Candler, Journal of Chemical Physics 143, 054304 (2015).



“Direct Diabatization and Analytic Representation of Coupled Potential Energy Surfaces and Couplings for the Reactive Quenching of the Excited 2Σ+ State of OH by Molecular Hydrogen,” Y. Shu, J. Kryven, A. G. S. de Oliveira-Filho, L. Zhao, G.-L. Song, S. L. Li, R. Meana-Pañeda, B. Fu, J. M. Bowman, and D. G. Truhlar, Journal of Chemical Physics 151, 104311/1-25 (2019).



“Potential Energy Surface for High-Energy N + N2 Collisions," Z. Varga and D. G. Truhlar, Physical Chemistry Chemical Physics 23, 26273-26284 (2021).


Licensing and downloading:

PIPFit 2022 is licensed under the Apache License, Version 2.0.
The manual of PIPFit 2022 is licensed under CC-BY-4.0.

Publications of results obtained with the PIPFit 2022 software should cite the program and/or the article describing the program.

No guarantee is made that this software is bug-free or suitable for specific applications, and no liability is accepted for any limitations in the mathematical methods and algorithms used within. No consulting or maintenance services are guaranteed or implied.

The use of the PIPFit 2022 implies acceptance of the terms of the licenses. The software may be downloaded here.

Links to Other Pages of Interest:

This document last modified on Feb. 28, 2022  by Software Manager