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560. MOPAC:A General Molecular-Orbital Program
(Version 5.0) (Vectorized IBM 3090 Version)
by James J. P. Stewart, Frank J. Seiler Research Laboratory, U.S. Air Force Academy, Colorado Springs, Colorado 80840 Converted by W. Hwung, Department of Chemistry, Indiana University, Bloomington, Indiana 47405 This program is a direct conversion of QCPE 455 for use on the IBM 3090 with vector facility. This system makes extensive use of IBM's ESSL (Engineering and Scientific Subroutine Library). MOPAC is a general-purpose semiempirical molecular- orbital package for the study of chemical reactions. The semiempirical Hamiltonians MNDO, MINDO/3 and AM1 are implemented; and calculations of vibrational spectra,thermodynamicquantities,isotopic substitution effects and force constants for molecules, ions and radicals are combined in a fully integrated package. One limitation is that RHF radicals cannot be used with FORCE unless the maximum number of allowed atoms is reduced. Within the electronic part of the calculation, eigenvectors and localized orbitals, chemical bond indices, charge, molecular orbitals, etc. are calculable. For studying chemical reactions, a transition-state location routine and a transition- state optimizing routine are available. The current incarnation of MOPAC (Version 5.0) represents a small but important improvement over earlier versions. The main changes are: 1. The default geometry optimizer has been changed from the Davidon-Fletcher-Powell to the Broyden- Fletcher-Goldfarb-Shanno formulation. This involves several small changes, e.g., the update formula for the inverse Hessian, augmenting the line minimization with a binary chop search method, and modifying the search direction step size. A significant increase in speed for geometry optimization has been observed (typically 15%) and some previously difficult systems now run smoothly. In several instances, a reduction of over 90% in time required has been obtained. The DFP method has been retained to allow comparison with previous geometry optimization. So far, no failures of the BFGS have been found. 2.Analytical derivatives are provided as an alternative to diatomic finite difference, but they provide more significant figures than finite difference. This is an adaptation of the program written by Yukio Yamaguchi and Michael J. S. Dewar. 3. To avoid accidental mixing of MNDO and AM1, a new keyword, PARASOK, is provided. Jobs requiring mixed parameter sets will not be run unless PARASOK is specified. 4. The vibrational analysis has been rewritten to describe molecular vibrations more accurately. 5. The DRC/IRC has been changed to allow easier analysis of the trajectories. 6. Keywords are now checked. Unrecognized keywords are flagged and the job stopped. This modification avoids wasting time when misspelled words are encountered. 7. In force calculations run with PRECISE, quartic contamination of the Hessian matrix has been annihilated, thus bringing about improved results (particularly for the trivial modes). 8. Changes have been made to allow increased precision in calculated quantities. Gradient norms can now be routinely reduced to below 0.001 Kcal/mole/Angstrom for rigid systems and to below about 0.1 for flexible systems. 9. A number of minor bugs have been corrected and minor improvements made, all of which are explained in the documentation. An extended description of the vibrational analysis and dynamic reaction coordinate, as well as explanations of new keywords and changes are also included in the documentation. FORTRAN (IBM VS2.2 PUTT 8801) Lines of Code: 22,989 |