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

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 O_2H^+ triatomic ion and its diatomic sub units upon dissociation with an unmatchable accuracy of fitting in comparison with the previous works (below 1 cm^-1 in the case of diatomic function and below 300 cm^-1 in the case of triatomic function). In general, this model is capable of modeling A_3 (H_3, O_3 etc.) and ABC (OCS, HCO^+ etc.) triatomic system in addition to the A_2B (O_2H^+) 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.以双曲正割基组为展开基底的置换不变组合双曲逆幂表示（CHIPR）多项式展开，被证实是描述多态耦合势能面（MSCPES）的高效模型。该模型已在O₂H⁺三原子离子及其解离过程中的双原子亚单元上进行了测试，其拟合精度相较以往研究无可比拟：双原子势能函数的拟合误差低于1 cm⁻¹，三原子势能函数的拟合误差低于300 cm⁻¹。总体而言，该模型不仅可用于A₂B型体系（如O₂H⁺）的建模，还可覆盖A₃型（如H₃、O₃等）与ABC型（如OCS、HCO⁺等）三原子体系。本文提供了一款Mathematica脚本文件（M-CHIPR.nb），可通过用户友好的方式完成双原子与三原子势能的拟合，且在所提供的.nb文件中，所有必要之处均配有相应解释。本代码的优势在于无需借助计算集群，仅需搭载优良处理器与内存的普通个人计算机即可运行；除此之外，其数值精度优异，且相较于其他语言编写的同类程序具备系统无关的一致性。