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Manuscript Title: MORATE: a program for direct dynamics calculations of chemical reaction rates by semiempirical molecular orbital theory.
Authors: T.N. Truong, D.-h. Lu, G.C. Lynch, Y.-P. Liu, V.S. Melissas, J.J.P. Stewart, R. Steckler, B.C. Garrett, A.D. Isaacson, A. Gonzalez-Lafont, S.N. Rai, G.C. Hancock, T. Joseph, D.G. Truhlar
Program title: MORATE version 4.5/P4.5-M5.03
Catalogue identifier: ACLM_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 75(1993)143
Programming language: Fortran.
Computer: Cray-2, Cray X-MP-EA, Cray Y-MP.
Operating system: UNICOS 6.1, UNICOS 6.1.6.
RAM: 700K words
Word size: 64
Peripherals: disc.
Keywords: Molecular physics, Chemical kinetics, Activation energy, Reaction path, Variational transition State theory, Semiclassical tunnelling, Semiempirical molecular Orbital methods, Direct dynamics.
Classification: 16.12.

Nature of problem:
The program calculates chemical reaction rate coefficients for unimolecular or bimolecular gas-phase reactions. Rate constants can be computed for canonical or microcanonical ensembles or for specific vibrational states of selected modes with translational, rotational, and other vibrational modes in thermal equilibrium.

Solution method:
Rate constants may be calculated using either conventional and/or variational transition state theory with multidimensional semiclassical tunneling contributions [1-3]. The potential energy surface is obtained by semiempirical molecular orbital calculations, and four different semiempirical molecular orbital methods [4-6], namely MINDO/3, MNDO, AM1, and PM3, may be used to represent the potential energy of interaction. First the program optimizes the geometries of the reactant(s), product(s), and conventional transition state (if any exists). Then the minimum energy path is calculated by one of several methods. The variational transition state of canonical variational theory, improved canonical variational theory, and/or microcanonical variational theory is found by interpolation of data stored on a grid. Tunneling probabilities are calculated analytically by the Wigner approximation, by numerical quadrature using semiclassical adiabatic methods for zero or small curvature of the reaction path, or by numerical quadrature using the large curvature (version 3) method. MORATE also calculates the equilibrium constant for the reaction, and it has an option to perform short runs in which conventional transition state theory rates are calculated without calculating a reaction path.

The maximum number of atoms, heavy atoms, and hydrogens allowed can be changed by resetting the NATOMS, MAXHEV, and MAXLIT parameters, respectively. Reactions involving up to two reactants and two products are allowed. Large-curvature tunneling is supported only in the harmonic approximation.

Unusual features:
The code is distributed with three ACSII documentation files (which we usually call "on-line manuals") containing detailed revision histories, instructions for input, and other useful information for users. One on-line manual is for POLYRATE-version 4.5.1, one is for MORATE, and the third is for MORATE, and the third is for MOPAC-version 5.0.

Running time:
This depends strongly on the particular system studied. For nine test runs distributed with the code, the computation times (in CPU seconds, in single-processor mode on the Cray X-MP-EA) are about 3000 seconds for the 9- and 19-atom variational transition state theory runs, 180 and 200 seconds for the 6-atom variational transition state theory runs, 10 and 60 seconds for the conventional transition state theory runs, 0.2 seconds for the restart 6-atom calculation, 6600 seconds for the 6-atom LCG3 calculation, and 400 seconds for the restart run on that system.

[1] D.G. Truhlar, A.D. Issacson, and B.C. Garrett, in: Theory of Chemical Reaction Dynamics, Vol.4, ed. M. Baer (CRC Press, Boca Raton, FL, 1985)pp. 65-137.
[2] B.C. Garrett, T. Joseph, T.N. Truong, and D.G. Truhlar, Chem. Phys. 136(1989)271.
[3] D.-h. Lu, T.N. Truong, V.S. Melissas, G.C. Lynch, Y.-P. Liu, B.C. Garrett, R. Steckler, A.D. Issacson, S.N. Rai, G.C. Hancock, J.G. Lauderdale, T. Joseph, and D.G. Truhlar, Comp. Phys. Commun. 71(1992)235.
[4] J.A. Pople and D.L. Beveridge, Approximate Molecular Orbital Theory (McGraw-Hill, New York, 1970).
[5] M.J.S. Dewar and W. Thiel, J. Amer. Chem. Soc. 99(1977)4899.
[6] J.J.P. Stewart, J. Computer-Aided Molecular Design 4(1990)1.