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.