Gaussian 03
Introduction
Starting from the basic laws of quantum mechanics, Gaussian predicts the energies, molecular structures, and vibrational frequencies of molecular systems, along with numerous molecular properties derived from these basic computation types.
Gaussion can be used to study molecules and reactions under a wide range of conditions, including both stable species and compounds which are difficult or impossible to observe experimentally such as short-lived intermediates and transition structures.
Investigating the Reactivity and Spectra of Large Molecules
Traditionally, proteins and other large biological molecules have been out of the reach of electronic structure methods. However, Gaussian 03’s ONIOM method overcomes these limitations. ONIOM first appeared in Gaussian 98, and several significant innovations in Gaussian 03 make it applicable to much larger molecules.
This computational technique models large molecules by defining two or three layers within the structure that are treated at different levels of accuracy. Calibration studies have demonstrated that the resulting predictions are essentially equivalent to those that would be produced by the high accuracy method.
The ONIOM facility in Gaussian 03 provides substantial performance gains for geometry optimizations via a quadratic coupled algorithm and the use of micro-iterations. In addition, the program’s option to include electronic embedding within ONIOM calculations enables both the steric and electrostatic properties of the entire molecule to be taken into account when modeling processes in the high accuracy layer (e.g., an enzyme’s active site). These techniques yield molecular structures and properties results that are in very good agreement with experiment.