MOPAC: An open-source semiempirical molecular orbital program

The Molecular Orbital PACkage (MOPAC) is a Fortran program that calculates chemical and physical properties of molecules, crystals, and nanostructures.MOPAC primarily operates as a command-line program that takes an input file defining a molecule by its approximate atomic coordinates and produces an output file containing the molecule's heat of formation and optimized coordinates alongside other useful properties.Keywords can then be added to the top of the input file to adjust MOPAC's behavior and request the use of other features.MOPAC is similar in function to ab initio quantum chemistry software, but it uses semiempirical models such as PM7 (Stewart, 2012) to reduce computational costs substantially while preserving as much accuracy as possible.