ABCRATE - A PROGRAM FOR THE CALCULATION OF ATOM-DIATOM REACTION-RATES

ABCRATE is a computer program for the calculation of atom-diatom chemi cal reaction rates for systems with collinear-dominated dynamics. The dynamical methods used are conventional or generalized transition stat e theory (GTST) and multidimensional semiclassical approximations for tunneling and nonclassical reflection. The GTST methods included in th is version of the program are the canonical and improved canonical var iational transition state theory (VTST) and the canonical unified stat istical (CUS) method. Rate constants may be calculated for canonical e nsembles or for specific vibrational states of selected modes with tra nslational, rotational, and other vibrational modes treated thermally. The potential energy surface required by the program may be a global or semiglobal analytic function. The reaction path is calculated as th e path of steepest descent in mass-scaled coordinates from a collinear saddle point, and vibrations transverse to the reaction path are trea ted by curvilinear internal coordinates. The vibrational modes are qua ntized, and anharmonicity may be included by various options, includin g the WKB approximation for bond stretches and the centrifugal oscilla tor approximation through quartic terms for the curvilinear bend coord inate. Tunneling probabilities are calculated by a variety of semiclas sical methods, in particular zero-curvature tunneling (ZCT), small-cur vature tunneling (SCT), large-curvature tunneling (LCT), least-action tunneling (LAT), and the microcanonical optimized multidimensional tun neling (mu LOMT) methods. (C) 1998 Elsevier Science B.V.