This is the official repository of the modern open-source version of MOPAC, which is now released under an LGPL license. This is a direct continuation of the commercial development and distribution of MOPAC, which ended at MOPAC 2016. Commercial versions of MOPAC are no longer supported, and all MOPAC users are encouraged to switch to the most recent open-source version.

MOPAC is actively maintained and curated by the Molecular Sciences Software Institute (MolSSI).

Open-source MOPAC is available through multiple distributon channels, and it can also be compiled from source using CMake. In addition to continuing the distribution of self-contained installers on the old commercial website and here on GitHub, MOPAC can also be installed using multiple package managers and accessed through containers.

Self-contained graphical installers for Linux, Mac, and Windows are available on GitHub for each release, which are constructed using the Qt Installer Framework.

While the installers are meant to be run from a desktop environment by default, they can also be run from a command line without user input. On Linux, the basic command-line installation syntax is:

./mopac-x.y.z-linux.run install --accept-licenses --confirm-command --root type_installation_directory_here

For more information on command-line installation, see the Qt Installer Framework Documentation.

Linux installations without a desktop environment may not have the shared libraries required for the graphical installers, and there have also been isolated reports of problems with the Qt installer on other platforms. A minimal, compressed-archive installer is available for each platform as an alternative for users that have problems with the Qt installer.

The minimum glibc version required for the precompiled version of MOPAC on Linux is currently 2.17.

The pre-built MOPAC executables use the RPATH system on Mac and Linux to connect with its shared libraries, including the libiomp5 Intel OpenMP redistributable library. The libiomp5 library is not properly versioned, and the recent version used by MOPAC is not compatible with older versions that might also exist on a user's machine. If a directory containing an old version of libiomp5 is in the shared library path (LD_LIBRARY_PATH on Linux, DYLD_LIBRARY_PATH on Mac), this will override the RPATH system, link MOPAC to the wrong library, and cause an error in MOPAC execution. On Mac, this can be fixed by switching the offending directories to the failsafe shared library path, DYLD_FALLBACK_LIBRARY_PATH. On Linux, the use of LD_LIBRARY_PATH is generally discouraged for widespread use, and there is no simple workaround available. The newer version of libiomp5 is backwards compatible, so replacing the offending version with the version used by MOPAC should preserve the functionality of other software that depends on the library.

The officially supported package manager for MOPAC is the conda-forge channel of Conda. MOPAC is also packaged by major Linux distributions including Fedora and Debian. It is also available in the Google Play store.

The official Docker and Apptainer (Singularity) containers for MOPAC 22.0.6 (Conda version) are developed and maintained by MolSSI Container Hub and are distributed by the MolSSI Docker Hub repository.

MOPAC is now built using a CMake 3.x build system with tests orchestrated using CTest. The minimum required CMake version is presently 3.14.

CMake performs out-of-source builds, with the canonical sequence of commands:

mkdir build
cd build
cmake ..
make

starting from the root directory of the MOPAC repository. MOPAC should build without any additional options if CMake successfully detects a Fortran compiler and BLAS/LAPACK libraries. Otherwise, the cmake .. command may require additional command-line options to specify a Fortran compiler (-DCMAKE_Fortran_COMPILER=...) or the path (-DMOPAC_LINK_PATH=...) and linker options (-DMOPAC_LINK=...) to link BLAS and LAPACK libraries to the MOPAC executable.

The CTest-based testing requires an installation of Python 3.x and Numpy that can be detected by CMake.

The main source for MOPAC documentation is presently its old online user manual.

There is a new documentation website under development, but it is not yet ready for general use.

To cite the use of open-source MOPAC in scientific publications, see the CITATION.cff file in this repository.