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Gaussian

Gaussian is one of the most widely used quantum chemistry software packages for predicting molecular structures, energies, vibrational spectra, thermochemical properties, electronic properties, and reaction pathways using ab initio, Density Functional Theory (DFT), Hartree–Fock (HF), and various post-Hartree–Fock methods.

Combined with its graphical interface GaussView, Gaussian provides an intuitive environment for building molecular structures, preparing input files, submitting calculations, and visualizing computational results.

Unlike the GAMESS documentation, which focuses on advanced multiconfigurational methods such as CASSCF, XMCQDPT, and Diabatization, this section is dedicated to performing routine electronic structure calculations including geometry optimization, vibrational analysis, reaction path calculations, and molecular property predictions.

Throughout these tutorials, optimized molecular geometries generated using Gaussian can later be exported to GAMESS or ORCA for advanced multireference calculations.

Official Resources

  • Gaussian Documentation

    Official reference manual describing Gaussian keywords, computational methods, and input options.

    Gaussian Documentation

  • Gaussian Website

    Official website for Gaussian software, licensing information, updates, and documentation.

    Visit Website

  • GaussView

    Graphical user interface for building molecules, preparing Gaussian jobs, and visualizing computational results.

    Learn More

Recommended Learning Workflow

If you are new to Gaussian and molecular electronic structure calculations, we recommend following the tutorials in the order shown below.

┌────────────────────┐
│  Introduction      │
└─────────┬──────────┘
          ▼
┌────────────────────┐
│    GaussView       │
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ Single Point Energy│
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ Geometry           │
│ Optimization       │
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ Frequency          │
│ Calculation        │
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ Optimization +     │
│ Frequency          │
└─────────┬──────────┘
          ▼
┌────────────────────┐
│  Transition State  │
│       Search       │
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ IRC                │
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ Coordinate Scan    │
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ NMR                │
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ Stability Analysis │
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ Export Geometry    │
│ to GAMESS / ORCA   │
└────────────────────┘

Each tutorial introduces one important aspect of molecular electronic structure calculations.

  • Introduction presents the Gaussian package, supported computational methods, and the overall workflow.
  • GaussView introduces molecular construction, visualization, and job preparation.
  • Single Point Energy explains how molecular energies are calculated for a fixed geometry.
  • Geometry Optimization determines the equilibrium molecular structure.
  • Frequency Analysis verifies optimized geometries and computes vibrational and thermochemical properties.
  • Optimization + Frequency combines geometry optimization with vibrational analysis in a single calculation.
  • IRC follows the minimum-energy reaction pathway from a transition state.
  • Coordinate Scan explores potential energy surfaces by varying internal coordinates.
  • NMR predicts magnetic shielding tensors and chemical shifts.
  • Stability Analysis verifies that the converged SCF solution corresponds to a stable electronic wavefunction.
  • Geometry Export prepares optimized structures for advanced electronic structure calculations using GAMESS or ORCA.

Tutorials

  • GaussView

    Learn molecular construction, editing, visualization, job preparation, and analysis of Gaussian calculations.

    Explore GaussView

  • Single Point Energy

    Compute the electronic energy of a molecule without changing its geometry.

    Explore Single Point Energy

  • Geometry Optimization

    Locate equilibrium molecular structures by minimizing the total electronic energy.

    Explore Geometry Optimization

  • Frequency Calculation

    Calculate vibrational frequencies, zero-point energy, and thermochemical properties.

    Explore Frequency

  • Optimization + Frequency

    Perform geometry optimization followed immediately by vibrational analysis.

    Explore Opt + Frequency

  • Transition State Optimization

    Perform transition state search for a molecule.

    Explore Transition state

  • Intrinsic Reaction Coordinate (IRC)

    Trace the reaction pathway connecting reactants, transition states, and products.

    Explore IRC

  • Coordinate Scan

    Investigate potential energy surfaces by scanning bond lengths, bond angles, or dihedral angles.

    Explore Scan

  • NMR Calculations

    Predict NMR shielding tensors and chemical shifts using the GIAO formalism.

    Explore NMR

  • Wavefunction Stability

    Verify that the converged Hartree–Fock or DFT wavefunction corresponds to the lowest-energy SCF solution.

    Explore Stability

Future Tutorials

The following topics will be included in future updates of the Gaussian documentation.

  • QST2

    Transition-state searches using optimized reactant and product structures.

  • QST3

    Transition-state searches using reactant, product, and transition-state guesses.

  • Exporting Gaussian Structures

    Convert optimized geometries into GAMESS and ORCA input files using Open Babel.

  • Population Analysis

    Mulliken, Natural Population Analysis (NPA), electrostatic potentials, and charge analysis.

  • Molecular Orbitals

    Visualization and interpretation of molecular orbitals, electron densities, and electrostatic potential maps.