This is the official repository of the modern open-source version of MOPAC, which is a direct continuation of the commercial development and distribution of MOPAC that ended at MOPAC 2016.
MOPAC is actively maintained and curated by the Molecular Sciences Software Institute (MolSSI).
For detailed information about MOPAC, see its website. A brief summary for developers is provided below.
MOPAC is a popular semiempirical quantum chemistry package that was first released in 1983. MOPAC can perform quantum mechanical calculations of molecules and materials, much like ab initio quantum chemistry packages such as Gaussian. Semiempirical calculations are around 1000x faster than ab initio calculations, but they are usually less accurate and less predictive because they rely on simplified models fit to experimental data rather than more complicated and comprehensive theories. The speed and ease-of-use of MOPAC make it a good teaching tool, either to teach physical chemistry concepts to students or to prepare for the use of more expensive quantum chemistry software. It can also be useful for high-throughput calculations in screening and informatics applications.
Pre-built versions of MOPAC on Linux, Mac, and Windows are available with every GitHub Release and also available on the Conda package manager using the command:
conda install -c conda-forge mopac
MOPAC can be built using its CMake build system. This repository has a GitHub Actions workflow to build MOPAC, and you can build it locally using the standard CMake out-of-source invocation:
mkdir build
cd build
cmake ..
make
MOPAC will build without any other CMake options if a Fortran compiler, BLAS/LAPACK, Python 3, and NumPy are found in the software environment.
To build with optional MolSSI Driver Interface(MDI) engine support, use the CMake command-line option -DMDI=ON.
While MOPAC is often used through its integration with other software such as WebMO, it is primarily a command-line program that operates through input and output files. Recent versions of MOPAC also has an application programming interface (API) for a subset of functionality.
Examples of command-line and API usage are provided in the /examples folder of this repository.
The recommended citation of open-source MOPAC in scientific publications is its archival copy on Zenodo at DOI:10.5281/zenodo.6511958.