MOPAC

MOPAC is a computational chemistry software package that implements a variety of semi-empirical quantum chemistry methods based on the neglect of diatomic differential overlap (NDDO) approximation and fit primarily for gas-phase thermochemistry. Modern versions of MOPAC support 83 elements of the periodic table (H-La, Lu-Bi as atoms, Ce-Yb as ionic sparkles) and have expanded functionality for solvated molecules, crystalline solids, and proteins. MOPAC was originally developed in Michael Dewar's research group in the early 1980s and released as public domain software on the Quantum Chemistry Program Exchange in 1983. It became commercial software in 1993, developed and distributed by Fujitsu, and Stewart Computational Chemistry took over commercial development and distribution in 2007. In 2022, it was released as open-source software on GitHub.