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Manuscript Title: POLYRATE: a general computer program for variational transition state theory and semiclassical tunneling calculations of chemical reaction rates.
Authors: A.D. Isaacson, D.G. Truhlar, S.N. Rai, R. Steckler, G.C. Hancock, B.C. Garrett, M.J. Redmon
Program title: POLYRATE
Catalogue identifier: ABBD_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 47(1987)91
Programming language: Fortran.
Computer: VAX 11/780.
Operating system: VAX/VMS VERSION 4.3.
RAM: 298K words
Word size: 32
Peripherals: disc.
Keywords: Molecular physics, Chemical kinetics, Activation energy, Variational transition State theory, Saddle point, Semiclassical Tunneling calculations, Reaction path, Gradient and hessian Of the potential energy, Scattering, Inelastic.
Classification: 16.12.

Nature of problem:
The program calculates unimolecular and bimolecular gas-phase chemical reaction rates of polyatomic species (and also of atoms and diatoms as special cases) from potential energy surfaces. Rate constants may be calculated for canonical or microcanonical ensembles. In addition, rates may be calculated for adiabatic and diabatic reactions in which one or more of the vibrational modes is restricted to the ground state or to the first excited state, while the translational, rotational, and remaining vibrational modes are treated thermally. The program may also be used to find stationary geometries of reactants, products, and transition states and to calculate multidimensional semiclassical tunneling probabilities and transmission coefficients.

Solution method:
Rate constants may be calculated using either conventional or variational transition state theory. A number of methods are available for calculating the reaction path and for treating anharmonicity of the vibrational modes of the reactants, products, and generalized- transition-state species, all under the assumption of independent normal modes. Semiclassical adiabatic approximations are used to calculate transmission coefficients for tunneling and nonclassical reflection.

Restrictions:
Gas-phase reactions involving up to ten atoms can be treated. The analysis of reactants and products can be performed for up to two reactants and two products.

Unusual features:
A restart option is available in which the program writes data it has calculated about the reactants, products, and generalized transition states to a disk file. Subsequent runs of POLYRATE can read this file and then proceed directly to the calculation of rate constants.

Running time:
5-20 minutes each (on VAX 11/780 with floating point accelerator) for the four test runs distributed with the program.