SPINKS (Spin Inversion Kinetics Suite): A Fully Automated Python–ORCA Framework for End-to-End Computation of Spin-Crossing Probabilities, Microcanonical, and Canonical Reaction Rate Constants

Abstract We present SPINKS (Spin Inversion Kinetics Suite), a freely available, fully automated Python–ORCA computational framework for an end-to-end evaluation of spin-forbidden reaction kinetics directly from an initial molecular geometry. SPINKS automatically generates, executes, monitors, and processes the ORCA electronic-structure calculations required to determine the minimum-energy crossing point (MECP) between two potential-energy surfaces. It then extracts the spin–orbit coupling (SOC), energy gradients, and Hessians required to construct the reaction coordinate and subsequently evaluates the reduced mass, crossing velocity, and vibrational and rovibrational densities of states. These quantities are used to calculate Landau–Zener and weak coupling spin-crossing probabilities and the corresponding microcanonical and canonical reaction rate constants within the framework of nonadiabatic statistical theory. The workflow automatically generates graphical visualizations and comprehensive text-based outputs while permitting user customization of ORCA input files throughout the calculation. SPINKS shows excellent agreement during validation tests against the independently developed Nonadiabatic Statistical Theory (NAST) package. The NAST program requires manual preparation and transfer of electronic-structure quantities, whereas SPINKS integrates ORCA-based electronic-structure calculations with nonadiabatic dynamics and kinetic calculations within a single end-to-end automated workflow. SPINKS is freely distributed and operates within an accessible software ecosystem based on the free and open-source Python language and the ORCA quantum-chemistry package, which is freely available for academic use. The SPINKS framework provides a practical, reproducible, and extensible platform for routine investigation of spin-forbidden chemical reactions.