Gaussian 09 is the latest in the Gaussian series of programs. It provides state-of-the-art capabilities for electronic structure modeling. Gaussian 09 is licensed for a wide variety of computer systems. All versions of Gaussian 09 contain every scientific/modeling feature, and none imposes any artifical limitations on calculations other than your computing resources and patience.

Modeling Antiferromagnetic Coupling in Gaussian 09

Antiferromagnetic coupling is an effect that is often important for molecules with high spin multiplicity.

Gaussian 09

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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’s ONIOM method overcomes these limitations. ONIOM first appeared in Gaussian 98, and several significant innovations in Gaussian 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 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.

New Features in Gaussian 09

Gaussian 09 offers new features and performance enhancements which will enable you to model molecular systems of increasing size, with more accuracy, and/or under a broader range of real world conditions.
 

  1. Model Reactions of Very Large Systems with ONIOM
    The ONIOM facility includes electronic embedding for MO:MM calculations whereby the electrostatic properties of the MM region are into account during computations on the QM region, and a fast, reliable optimization algorithm that takes the coupling between atoms in the model system and those only in the MM layer into account and uses microiterations for the MM layer between traditional optimization steps on the real system. Gaussian 09 provides many additional enhancements to the ONIOM facility, including the following:

    • Transition state optimizations.

    • Much faster IRC calculations.

    • Frequency calculations including electronic embedding.

    • Calculations in solution.

    • General performance enhancements.

    • Fully customizable MM force fields.

    • New implementations of AM1, PM3, PM3MM, PM6 and
      PDDG semi-empirical methods with true analytic gradients
      and frequencies (parameters also fully customizable).

  2. Study Excited States in the Gas Phase and in Solution
    Gaussian 09 includes many new features intended for studying excited state systems, reactions and processes:

    • Analytic time-dependent DFT (TD-DFT) gradients.

    • The EOM-CCSD method.

    • State-specific solvation excitations and de-excitations.

    • Franck-Condon and Herzberg-Teller analysis (and FCHT).

    • Full support for CIS and TD-DFT calculations in solution (equilibrium and non-equilibrium).

Many More New Features:

  • Significantly enhanced solvation features: In addition to the excited state features mentioned above, the SCRF facility also includes a new implementation incorporating a continuous surface charge formalism that ensures continuity, smoothness and robustness of the reaction field, and which also has continuous derivatives with respect to atomic positions and external perturbing fields. This results in faster, more reliable optimizations (taking no more steps than the gas phase) and accurate frequency calculations in solution.

  • Analytic gradients for the Brueckner Doubles (BD) method.

  • Additional spectra prediction: analytic DFT first hyperpolarizabilities and numeric second hyperpolarizabilities, analytic static and dynamic Raman intensities, analytic dynamic ROA intensities, improved anharmonic frequency calculations.

  • Population analysis of individual orbitals.

  • Fragment-based initial guess and population analysis.

  • Ease of use features: reliable restarts of many more calculation types, fragment definitions within molecule specifications, freezing atoms by type, fragment, ONIOM layer and/or residue, selecting/sorting normal modes of interest during a frequency calculation, saving/reading post-SCF amplitudes, saving/reading normal modes.

  • Many new DFT functionals, including ones incorporating long range corrections, empirical dispersion, and double hybrids.

  • Substantial performance improvements throughout the program, including optimizations for large molecules, frequency calculations on large molecules (as much as 16x in parallel), IRC calculations (~3x faster), and optical rotations (~2x faster).

Spin-Spin Coupling

Determining Conformations via Spin-Spin Coupling Constants

Conformational 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 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 Systems

Gaussian 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 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 can also model compounds’ band gaps.

Modeling Solvent Effects

Modeling Solvent Effects on Reactions and Molecular Properties

Molecular 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 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.

Computation Features

Gaussian can compute a very wide range of spectra and spectroscopic properties. These include:

  • IR and Raman

  • Pre-resonance Raman

  • UV-Visible

  • NMR

  • Vibrational circular dichroism (VCD)

  • Electronic circular dichroism (ECD)

  • Optical rotary dispersion (ORD)

  • Harmonic vibration-rotation coupling

  • Anharmonic vibration and vibration-rotation coupling

  • g tensors and other hyperfine spectra tensors 


Gaussian 09W

Gaussian 09W is a complete implementation of Gaussian 09 for the Windows environment.

Gaussian 09W can be used to model many properties

  • Energies using a wide variety of methods, including Hartree-Fock, Density Functional Theory, MP2, Coupled Cluster, and high accuracy methods like G3, CBS-QB3 and W1U.

  • Geometries of equilibrium structures and transition states (optimized in redundant internal coordinates for speed), including QST2 transition structure searching.

  • Vibrational spectra, including IR, non-resonant and pre-resonance Raman intensities, anharmonic vibrational analysis and vibration-rotation coupling.

  • Magnetic properties, including NMR chem-ical shifts and spin-spin coupling constants.

  • Spectra of chiral molecules: optical rotations, VCD and ROA.

  • G tensors and other contributions to hyper-fine spectra.

Gaussian 09W can study compounds and reactions under a wide range of conditions:

  • In the gas phase and in solution.

  • In the solid state, using the Periodic Boundary Conditions facility.

  • Excited states can be studied with several methods: CASSCF and RASSCF, Time Dependent DFT and SAC-CI.

  • The Atom Centered Density Matrix Propagation (ADMP) method can be used to perform molecular dynamics simulations in order to study reaction paths and product state distributions.


Gaussian 09M

Gaussian 09M is a complete implementation of Gaussian 09 for the Mac OS X environment.

Gaussian 09M can be used to model many properties:

  • Energies using a wide variety of methods, including Hartree-Fock, Density Functional Theory, MP2, Coupled Cluster, and high accuracy methods like G3, CBS-QB3 and W1U.

  • Geometries of equilibrium structures and transition states (optimized in redundant internal coordinates for speed), including QST2 transition structure searching.

  • Vibrational spectra, including IR, non-resonant and pre-resonance Raman intensities, anharmonic vibrational analysis and vibration-rotation coupling.

  • Magnetic properties, including NMR chem-ical shifts and spin-spin coupling constants.

  • Spectra of chiral molecules: optical rotations, VCD and ROA.

  • G tensors and other contributions to hyperfine spectra.

    • In the gas phase and in solution.

    • In the solid state, using the Periodic Boundary Conditions facility.

    • Excited states can be studied with several methods: CASSCF and RASSCF, Time Dependent DFT and SAC-CI.

    • The Atom Centered Density Matrix Propagation (ADMP) method can be used to perform molecular dynamics simulations in order to study reaction paths and product state distributions.


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