MOPAC 93 (the successor of MOPAC 6.0) is a general-purpose semiempirical molecular orbital package for the study of solid state and molecular structures and reactions, written by James J.P. Stewart.
The semiempirical hamiltonians MNDO, MINDO/3, AM1 and PM3 are used in the electronic part of the calculation to obtain molecular orbitals, the heat of formation and its derivative with respect to molecular geometry. Using these results MOPAC calculates the vibrational spectra, thermodynamic quantities, isotopic substitution effects and force constants for molecules, radicals, ions, and polymers.
For studying chemical reactions, a transition state location routine and two transition state optimizing routines are available.
The simplest description of how MOPAC works is that the user creates a data-file (extension .dat) which describes a molecular system and specifies what kind of calculations and output are desired.
The user then commands MOPAC to carry out the calculation using that data-file. The CAOS/CAMM menu offers a list of input files and an overview of available queues, from which one selects the appropriate entries.
Short: less then 10 minutes, medium: less then one hour, long: up to six hours. If jobs run out of time, restart files are written and the jobs can be resumed after adding the keyword RESTART to the input file.
Finally the user extracts the desired output on the system from the output files (.out and .arc files, supplementary files depending on keywords) created by MOPAC.

MOLDEN reads the information from the output files; i.e. the geometry, reaction coordinates, and vibrations are read and displayed.
Orbital coefficients can be shown after the keywords VECTORS and GRAPH have been specified.

SYBYL displays MOPAC information if all the necessary files are present, which is most conveniently accomplisehd by running the job from within Sybyl. For orbitals the keyword VECTORS and GRAPH can be switched on in a menu.

Source: MOPAC 93, by Dr. J.J.P. Stewart and Fujitsu Limited, Tokyo, Japan.
Academic license through QCPE, no. 455.

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