Eyringpy is a program for computing rate constants using the transition state theory (TST), in the gas phase and in solution. The Gibbs activation energy is obtained by computing from scratch the canonical partition functions. Unimolecular and bimolecular reactions with one or two products are supported. Rate constants of bimolecular reactions involving the formation of pre-reactive and/or product complexes are also estimated. The reaction symmetry is considered. One-dimensional Wigner and Eckart tunneling corrections are also available. To compute rate constants in solution, Eyringpy employs the Collins–Kimball theory to include the diffusion-limit, the Marcus theory for electron transfer (ET) processes, and the molar fractions to account for the effect of pH in aqueous reactions. Two versions are available.

In Eyringpy2.0, the IRC-Analysis is available for monitoring the evolution of primitive changes along the intrinsic reaction coordinate (IRC). For now, the available primitive changes that can be studied are the bond distances, angles, Wiberg bond indices, natural charges, dipole moment, orbital energies (and related properties), and reaction forces. A spline interpolator from Python's Scipy library is used to smooth the energy profiles. In addition, a discriminator to remove points causing noise in the energy profiles is also available. The Python's Matplotlib library is used for plotting the evolution of the primitive changes along the IRC.

Eyringpy is compatible with Gaussian output files. Since version 2.1, Eyringpy is compatible with Gaussian and ORCA output files.