## Abstract

POLYRATE is a computer program for the calculation of chemical reaction rates of polyatomic species (and also atoms and diatoms as special cases). Version 1.1 was submitted to the CPC Program Library in 1987, and since that time we have considerably improved the program and made it more portable, and we have added several new capabilities, resulting in the present improved version 4. The methods used are variational or conventional transition state theory and multidimensional semiclassical adiabatic and large-curvature approximations for tunneling and nonclassical reflection. Rate constants may be calculated for canonical or microcanonical ensembles or for specific vibrational states of selected modes with translational, rotational, and other vibrational modes treated thermally. Bimolecular and unimolecular reactions and gas-phase, solid-state, and gas-solid interface reactions are all included. Potential energy surfaces may be global analytic functions or implicit functions defined by interpolation from input energies, gradients, and force constants (Hessian matrices) at selected points on a reaction path. The program calculates reaction paths by the Euler, Euler stabilization, or Page-McIver methods. Variational transition states are optimized from among a one-parameter sequence of generalized transition states orthogonal to the reaction path. Tunneling probabilities are calculated by numerical quadrature, using either the centrifugal-dominat-small-curvature approximation, the large-curvature-version-3 approximation, and / or methods that were available earlier. In the large curvature case the tunneling probabilities may be summed over final vibrational states for exoergic reactions or initial vibrational states for endoergic reactions.

Original language | English (US) |
---|---|

Pages (from-to) | 235-262 |

Number of pages | 28 |

Journal | Computer Physics Communications |

Volume | 71 |

Issue number | 3 |

DOIs | |

State | Published - Sep 1992 |

### Bibliographical note

Funding Information:The authors are grateful to Ron Duchovic, Ken Dykema, Alan Earhart, Angels Gonzalez-Lafont, Jason Goeppinger, Mike Redmon, Greg Schenter, and Rex Skodje for helpful discussions or other contributions to the development effort or earlier versions. This work was supported in part by the US Department of Energy, Office of Basic Energy Sciences under grant DOE/FGO2-86ER13579 (principal investigator: DGT). One of the authors (BCG) was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, US Department of Energy under contract DE-ACO6-76RLO 1830 with Battelle Memorial Institute which operates the Pacific Northwest Laboratory.