POLYRATE-6.5 - A NEW VERSION OF A COMPUTER-PROGRAM FOR THE CALCULATION OF CHEMICAL-REACTION RATES FOR POLYATOMICS

POLYRATE is a computer program for the calculation of chemical reactio n rates of polyatomic species (and also atoms and diatoms as special c ases), Version 1.1 was submitted to the CPC Program Library in 1987, a nd version 4.0.1 was submitted in 1992, Since that time many new capab ilities have been added, old ones have been improved, and the code has been made more portable and user-friendly, resulting in the present i mproved version 6.5. The methods used are variational or conventional transition state theory and multidimensional semiclassical adiabatic a nd large-curvature approximations for tunneling and nonclassical refle ction, Rate constants may be calculated for canonical or microcanonica l ensembles or for specific vibrational states of selected modes with translational, rotational, and other vibrational modes treated thermal ly. 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 define d by interpolation from input energies, gradients, and force constants (Hessian matrices) at selected points on a reaction path. The data ne eded for the dynamics calculations may also be calculated from a globa l potential energy surface with more accurate calculations at stationa ry points. The program calculates reaction paths by the Euler, Euler s tabilization, or Page-McIver methods. Variational transition states ar e optimized from among a one-parameter sequence of generalized transit ion states orthogonal to the reaction path. Tunneling probabilities ar e calculated by numerical quadrature, using either the centrifugal-dom inant-small-curvature approximation, the large-curvature-version-3 app roximation, and/or optimized multidimensional tunneling approximations . In the large-curvature case the tunneling probabilities may be summe d over final vibrational states for exoergic reactions or initial vibr ational states for endoergic reactions.