In the News..28-06-2006 GaussView 4 - coming soon Gaussian Quick Launch & Job Schemes: Launch Gaussian without saving the molecule first, and save commonly-used calculation types as templates. 3D Scan Plots: Results from Scan calculations over 2 variables are displayed as a 3D plot. Greatly expanded plot features for Spectra: Support for UV/Visual spectra and the ability to customize all spectrum plots,including frequency scaling. Enhanced Fragment Library support. Contour plots: Display surface slices. Also, much faster surface generation. Movie files: Generate animations of geometry optimizations, IRCs and other calculation types as well as molecular vibrations from frequency jobs. |
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Gaussian 03/03W/03MFeatures
Gaussian 03 is the latest in the Gaussian series of electronic structure programs. Gaussian 03 is used by chemists, chemical engineers, biochemists, physicists and others for research in established and emerging areas of chemical interest. 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. It 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 MoleculesTraditionally, 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. For example, researchers are currently studying excited states of bacteriorhodopsin (illustrated below) using an ONIOM(MO:MM) model, as a first step in understanding the means by which this species generates energy within a cell. In this two-layer approach, the active site is treated using an electronic structure method while the rest of the system is modeled with molecular mechanics. Electronic embedding, which includes the electrostatics of the protein environment within the QM calculation of the active site, is essential to accurate predictions of the molecule’s UV-Visible spectrum. The ONIOM method is also applicable to large molecules in many other areas, including enzyme reactions, reaction mechanisms for organic systems, cluster models of surfaces and surface reactions, photochemical processes of organic species, substituent effects and reactivity of organic and organometallic compounds, and homogeneous catalysis Other new ONIOM related features in Gaussian 03
Determining Conformations via Spin-Spin Coupling ConstantsConformational analysis is a difficult problem when studying new compounds for which X-ray structures are not available. Magnetic shielding data in NMR spectra provides information about the connectivity between the various atoms within a molecule. Spin-spin coupling constants can aid in identifying specific conformations of molecules because they depend on the torsion angles with the molecular structure. Gaussian 03 can predict spin-spin coupling constants in addition to the NMR shielding and chemical shifts available previously. Computing these constants for different conformations and then comparing predicted and observed spectra makes it possible to identify the specific conformations that were observed. In addition, the assignment of observed peaks to specific atoms is greatly facilitated. Studying Periodic SystemsGaussian 03 expands the range of chemical systems that it can model to periodic systems such as polymers and crystals via its periodic boundary conditions (PBC) methods. The PBC technique models these systems as repeating unit cells in order to determine the structure and bulk properties of the compound. For example, Gaussian 03 can predict the equilibrium geometries and transition structures of polymers. It can also study polymer reactivity by predicting isomerization energies, reaction energetics, and so on, allowing the decomposition, degradation, and combustion of materials to be studied. Gaussian 03 can also model compounds’ band gaps Other PBC capabilities in Gaussian 032D PBC methods can be used to model surface chemistry, such as reactions on surfaces and catalysis. In addition, using Gaussian 03 allows you to study the same problem using a surface model and/or a cluster model, using the same basis set and Hartree-Fock or DFT theoretical method in both cases. Using Gaussian 03 enables you to choose the appropriate approach for the system you are studying, rather than being forced to frame the problem to fit the capabilities and limitations of a particular model. 3D PBC: The structures and available bulk properties of crystals and other three-dimensional periodic systems can be predicted Predicting SpectraGaussian 03 can compute a very wide range of spectra and spectroscopic properties. These include:
Modeling Solvent Effects on Reactions and Molecular PropertiesMolecular properties and chemical reactions often vary considerably between the gas phase and in solution. For example, low lying conformations can have quite different energies in the gas phase and in solution (and in different solvents), conformation equilibria can differ, and reactions can take significantly different paths. Gaussian 03 offers the Polarizable Continuum Model (PCM) for modeling system in solution. This approach represents the solvent as a polarizable continuum and places the solute in a cavity within the solvent. |