MOPAC is a general-purpose semi-empirical molecular orbital package for the
study of chemical structures and reactions. The semi-empirical Hamiltonians
MNDO, MINDO/3, AM1, and PM3 are used in the electronic part of the
calculation to obtain molecular orbitals, the heat of formation and its
derivative with respect to molecular geometry. Using these results MOPAC
calculates the vibrational spectra, thermodynamic quantities, isotopic
substitution effects and force constants for molecules, radicals, ions, and
polymers.  For studying chemical reactions, a transition state location
routine and two transition state optimizing routines are available.