mop2007 panel MOPAC is a general-purpose semiempirical quantum mechanics package for the study of chemical properties and reactions in gas, solution or solid-state. MOPAC directly predicts numerous chemical and physical properties such as Gibbs free energies, activation energies, reaction paths, dipole moments, non-linear optical properties and infrared spectra. It is also used as the basis of quantitative structure-property (or activity) relationships (QSAR), to predict a wide variety of biological and other properties such as carcinogenicity, vapor pressure, water solubility, and reaction rates.
It is based on early work of the Dewar group and now maintained and developed by James J.P. Stewart.
It is to be highly appreciated, that James J.P. Stewart recently has released MOPAC2007 (and now MOPAC2009) as a free product for academic work. It is a greatly improved program, compared to the last public offering, Mopac7. It has new hamiltonians PM6 and RM1, and improved parameterized PM3, AM1, and MNDO hamiltonians. It exists in binary versions for Windows and Linux computer systems. You find the main features here.
Mopac is celebrated not for its accuracy, which was just moderate but has improved considerably in the recent versions, but for its blazing speed which enables it to compute very large systems, e.g. proteins of several 10'000 atoms.

Similarly to most other QC-programs MOPAC is driven by input files which the user creates with an editor according to certain rules of syntax. The bare minimum is a rough quantitative chemical structure, e.g. in the form of atomsymbols and their three cartesian coordinates, keywords for the kind of computation to be performed and some qualifiers. This data-file (extension .dat) is then fed to Mopac and the calculation started.

The script mop2009, see its panel above, allows to configure a Mopac input file with the main features of the program. Before submitting one can manually modify it, and then run it with Mopac2009. Its foremost purpose is to support the user with the most common keywords and their syntax, details I usually soon forget if I do not use the program daily!

mopac howtomop2009 supports the following features of MOPAC:
- All Hamiltonians (except PM5)
- SCF Energy
- Structure Optimization
- Transition State Optimization
- Vibrational Frequencies
- Thermochemical Calculations
- Molecular Orbitals
- Others: to be filled in by user

Instructions at left, concernng usage of the script, are opened when pressing 'Mopac2009 how to'.

Unless the systems are very large Mopac runs last seldom more than a few minutes. If jobs run longer than 1 hour, 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 of the calculation from the output files (extension .out) and the summary file (extension .arc) created by MOPAC. The script calls an editor which opens the output file automatically, once Mopac has terminated.

A note of warning is appropriate: The old Mopac7 with the best hamiltonians AM1 and PM3 can produce utter nonsense, even if used judiciously. Don't believe any of its results without proper checking 'optimized' structure, and especially: look at the orbitals produced. The same hamiltonians under Mopac2009 now find the correct stationary structures.

MOLDEN is able to read the information from the output files; i.e. structure, molecular orbitals, density, reaction coordinates, and vibrations (if computed) are read and displayed.

WebMO, for Unix/Linux and Windows machines, embeds Mopac2009 in a more complete way compared to the script above, see one page back. mop2009 addresses the Windows community. It is a very modest GUI for composing Mopac jobs and can easily be improved similar to the author's scripts for (PC-)Gamess.


New Mop2009(536 kB): Runscript, original Mopac instructions, and several examples in a 'tests' subdirectory are included in the archive. You have to get MOPAC2009.exe from here and copy it into the same directory as the files extracted from Having done this go into this directory and click on mop2009.exe. As a starter run the preconfigured optimization of Methanol (see above, top). In less than 0.1 sec the output can be inspected!
Last update Jul 02, 2010

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