What MOPAC is

  MOPAC (Molecular Orbital PACkage) is a semiempirical quantum chemistry program based on Dewar and Thiel's NDDO approximation.    Most users use MOPAC with a Graphical User Interface.
MOPAC2016   MOPAC2016 is MOPAC2012 with improved handling of biomolecules.  If a bug is detected, please send a message by E-mail to, along with an example illustrating the bug.  If you qualify for Academic not-for-profit use and already have a password for MOPAC 2012, go straight to download, otherwise request a password and download.  For commercial and governmental prices, see Prices.
Instructions for use with Chem3D.

Commercial users in Europe and America, please contact CAChe Research (see Resellers)
Commercial users in Japan, please contact Ryoka Systems
Commercial users in Korea, please contact  KREIS I&C

PM7   PM7 is a modified form of PM6. A few errors in NDDO theory that affect large systems have been removed.  All atomic and diatomic parameters were re-optimized.  Average errors in organic compounds have been reduced by ~10%, and errors in large organics and solids have been significantly reduced, see PM7 Accuracy.
Recent publications   Abstracts of recent articles, and links to files that were used for generating the results, can be viewed
GPU   Recently, MOPAC2016 was modified to allow NVIDIA GPU acceleration to be used, for details, see GPU, this allows large systems that do not use MOZYME to run between two to just over three times faster than with just MKL and parallelization. MOZYME jobs do not run faster when a GPU chip is used. Read Requirements for GPU MOPAC before installing it.
and Citations
  MOPAC2016   MOPAC2009PM6PM7
Instructions and Manual   A manual is available for MOPAC2016.  Please try finding answers to questions there before sending an E-mail message requesting help. For individual topics of interest, see Discussion Topics.
Maintenance record     MOPAC2016 is under constant maintenance.  If your copy of MOPAC2016 does not work correctly, check the maintenance record to see if there is a more up-to-date version.


  PM6 is a re-parameterization of the NDDO method.  Three modifications to the approximations were made, these mainly affect the way the core-core interaction was defined.  Parameters were optimized for most elements, the exceptions being 12 of the lanthanides and all of the actinides.  The lanthanides can be represented by sparkles.  For details, see the on-line PM6 journal article, and its supplementary material.

Downloads of source and  binaries for the various older versions of MOPAC are available, as well as utility programs such as BZ and MAKPOL.

History   MOPAC was started in 1981, and has been under continuous development since then.
Older MOPAC Programs   MOPAC2012 is MOPAC2009 plus PM7 and PM7-TS. 
MOPAC2009 is MOPAC2007 plus the MOZYME function.  MOZYME is a linear-scaling SCF method that allows systems of up to 15,000 atoms to be modeled.
MOPAC2007 was an improved version of MOPAC 7.1. In addition to the methods in MOPAC 7.1, it also included RM1 and PM6.
MOPAC 7.1 is a FORTRAN 90 version of MOPAC 7. It supports the methods: MNDO, AM1, and PM3, as well as Sparkle/AM1 for the lanthanides. All published NDDO parameter sets were supported. It is fully in the public domain. (Download source)
Availability   32 and 64 bit Windows, 32 bit and 64 bit Linux, CentOS-5, CentOS-6, CentOS-7, and 64 bit Mac versions are supported.
Cooperative Development   The purpose of this site is to encourage cooperative development.  There is a default mechanism for contributing improvements.
Acknowledgment   This work was funded by the National Institute of General Medical Sciences (NIGMS), Grant No. 2 4R44GM108085-02
Example files    co2.mop
Contacts   James Stewart, 15210 Paddington Circle, Colorado Springs, CO 80921
 E-mail :

SKYPE: Jimmy.Stewart2 (between 1500 and 2200 GMT)

The mark "MOPAC" is a trademark of James Stewart
Copyright 2007, Stewart Computational Chemistry.