Eyringpy is a program designed to compute rate constants using Transition State Theory (TST) and Variational Transition State Theory (VTST), both in the gas phase and in solution. The Gibbs activation energy is obtained from canonical partition functions calculated from first principles. The program supports unimolecular and bimolecular reactions with one or two products. It can also estimate the rate constants of bimolecular reactions involving pre-reactive and/or product complexes. Reaction symmetry is included, and one-dimensional Wigner and Eckart tunneling corrections are available.

For solution-phase reactions, Eyringpy incorporates Collins–Kimball theory to account for diffusion limits, Marcus theory for electron transfer (ET) processes, and molar fractions to evaluate pH effects in aqueous media.

The latest version, Eyringpy, includes an IRC-Analysis module that monitors the evolution of primitive changes along the intrinsic reaction coordinate (IRC). Currently available analyses include bond distances, bond angles, Wiberg bond indices, natural charges, dipole moments, orbital energies and related properties, as well as reaction forces.

To improve accuracy, energy profiles are smoothed using a spline interpolator from Python’s SciPy library, while a discriminator removes noisy data points. Visualization of the evolution of primitive changes is performed with Python’s Matplotlib library.