MORATE-6.5 - A NEW VERSION OF A COMPUTER-PROGRAM FOR DIRECT DYNAMICS CALCULATIONS OF CHEMICAL-REACTION RATE CONSTANTS

MORATE (Molecular Orbital RATE calculations) is a computer program for direct dynamics calculations of unimolecular and bimolecular rate con stants of gas-phase chemical reactions involving atoms, diatoms, or po lyatomic species. The dynamical methods used are conventional or varia tional transition state theory and multidimensional semiclassical appr oximations for tunneling and nonclassical reflection. Variational tran sition states are found by a one-dimensional search of generalized-tra nsition-state dividing surfaces perpendicular to the minimum-energy pa th, and tunneling probabilities are evaluated by multidimensional semi classical algorithms, including the small-curvature and large-curvatur e tunneling approximations and the microcanonical optimized multidimen sional tunneling approximation, The computer program is a conveniently interfaced package consisting of the POLYRATE program, version 6.5, f or dynamical rate constant calculations, and the MOPAC program, versio n 5.05mn, for semiempirical electronic structure computations. In sing le-level mode, the potential energies, gradients, and higher derivativ es of the potential are computed whenever needed by electronic structu re calculations employing semiempirical molecular orbital theory witho ut the intermediary of a global or semiglobal fit. All semiempirical m ethods available in MOPAC, in particular MIND0/3, MNDO, AM1, and PM3, can be called on to calculate the potential, gradient, or Hessian, as required at various steps of the dynamics calculations, and, in additi on, the code has flexible options for electronic structure calculation s with neglect of diatomic differential overlap and specific reaction parameters (NDDO-SRP). In dual-level mode, MIND0/3, MNDO, AMI, PM3, or NDDO-SRP is used as a lower level to calculate the reaction path, and interpolated corrections to energies and frequencies are added; these corrections are based on higher-level data read from an external file .