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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
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