Using Quantum Mechanics Methods

In addition to total energy and gradient, HyperChem can use quantum mechanical methods to calculate several other properties. The properties include the dipole moment, total electron density, total spin density, electrostatic potential, heats of formation, orbital energy levels, vibrational normal modes and frequencies, infrared spectrum intensities, and ultraviolet-visible spectrum frequencies and intensities. The HyperChem log file includes energy, gradient, and dipole values, while HIN files store atomic charge values. 

Combined Quantum and Molecular Mechanical Simulations. A recentiy developed technique is one wherein a molecular dynamics simulation includes the treatment of some part of the system with a quantum mechanical technique. This approach, QM/MM, is similar to the coupled quantum and molecular mechanical methods introduced by Warshel and Karplus (45) and at the heart of the MMI, MMP2, and MM3 programs by AUinger (60). These latter programs use quantum mechanical methods to treat the TT-systems of the stmctures in question separately from the sigma framework. 

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