Implementation of Rydberg-Klein-Rees (RKR) Method to Compute Molecular Potential Energy Curves in C++ as a User-Friendly, Standalone Executable

We present a user-friendly, standalone C++ program for generating molecular potential energy curves using the Rydberg--Klein--Rees (RKR) method and experimentally determined spectroscopic constants. The program uses the open-source GNU Scientific Library (GSL) for numerical computations and provides a graphical user interface for entering constants and calculation parameters. It also visualizes the resulting potential energy curve in the same interface for quick verification and exports it to a plain-text format compatible with the LEVEL 8.0 program, enabling downstream calculations such as Franck--Condon factors for comparing the rovibrational peaks with the experimentally obtained spectra. The program is benchmarked against a proof-of-concept MATLAB script developed by our group as well as the RKR script in the pre-existing Optimizer MATLAB package. It shows significant improvement in compute-time while maintaining the same double-precision (64-bit floating-point) numerical accuracy. Most importantly, the program is free-to-use under the GNU General Public License and is purely standalone. Therefore, it is accessible to universities and colleges without relying on proprietary software or requiring a complex installation and external dependencies.