M-CHIPR: A Mathematica program for constructing multi-state coupled adiabatic potential energy functions in triatomic molecule using many body partitioning approach

Abstract

The permutationally invariant combined hyperbolic inverse power representation (CHIPR) polynomial expansion in terms of hyperbolic secant basis proves to be an efficient model in describing the multi state coupled potential energy surface (MSCPES) and this fact was tested on the O2H+ triatomic ion and its diatomic sub units upon dissociation with an unmatchable accuracy of fitting in comparison with the previous works (below 1cm−1 in the case of diatomic function and below 300cm−1 in the case of triatomic function). In general, this model is capable of modeling A3 (H3, O3 etc.) and ABC (OCS, HCO+ etc.) triatomic system in addition to the A2B (O2H+) system. This paper presents a Mathematica notebook (M-CHIPR.nb file) to perform the fitting of di and triatomic potentials in a user friendly manner with proper explanations written along side wherever required in the .nb file supplied. The advantage of this code is that the computing clusters are not required to use it and can be run in normal pc with good processor and memory, apart from its numerical accuracy and the system independent consistency over the similar programs written in other languages. Program summaryProgram title: M-CHIPRCPC Library link to program files:https://doi.org/10.17632/4mbydkzyts.1Licensing provisions: GPLv3Programming language: Wolfram Mathematica version12 or higherNature of problem: Finding an multi-variable Mathematica combined hyperbolic inverse power representation (M-CHIPR) function to describe a multi state coupled potential energy surface for a typical diatomic and triatomic molecule via extensive nonlinear regression method involving hundreds of optimizable variables with minimal fitting error with respect to the raw data points.Solution method: Default Mathematica implementation of nonlinear least square fitting of ab initio points to obtain a well optimized model function having ability to accurately predicting the data behavior.Additional comments including restrictions and unusual features: The entire work was tested on Apple Mac pc with Intel i7 processor having 4 cores. The version of Mathematica is 12 and therefore, the users are advised to test the supplied notebook with the same version and beyond to avoid incompatibility issues.