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MO-G (previously MOPAC), the Molecular Orbital Package, developed by James J. P. Stewart, provides a choice of methods for computing electronic properties of molecules. Scigress provides access to MO-G methods through a Windows environment.

The Scigress MO-G application determines both an optimum geometry and the electronic properties of molecules by solving the Schrödinger equation using the semi-empirical Hamiltonians AM1, PM3 and PM5, developed by M. J. S. Dewar and J. J. P. Stewart respectively. Scigress also supports the older parameter sets, MNDO and MINDO/3, and the newer parameter set, MNDOd. In addition, Scigress extends AM1 to AM1/d.

The molecular orbitals, heat of formation, and molecular geometry derivatives obtained are used to calculate vibrational spectra, molecular geometries, force constants, and other properties of molecules, radicals, and ions. These quantities are used to calculate reaction trajectories and to investigate chemical reactions by locating transition states.

MO-G can calculate the geometry, energetics and reaction profiles of molecules in their excited states. It can include solvent effects in these calculations. Excited state calculations are important in simulation of photochemical processes. MO-G calculates heats of formation, rather than the energy required to separate the molecule into isolated nuclei and electrons as in quantum-chemical methods such as Extended Hückel Theory and ZINDO.

Although MO-G uses many concepts from quantum theory, thermodynamics, and advanced mathematics, a detailed understanding of these areas is not necessary. MO-G was written and designed with non-theoretical chemists in mind.

To find more information please see standalone version of MO-G.