6-31g*

Definition

The 6-31g* basis set is a commonly used split-valence basis set in quantum chemistry that includes polarization functions for the description of electron distribution in molecules. It consists of two sets of Gaussian-type orbitals, with six functions for core electrons and three functions for valence electrons, plus an additional set of polarization functions. This allows for more accurate calculations of molecular properties compared to simpler basis sets without polarization.

5 Must Know Facts For Your Next Test

1. The '6-31' notation indicates a split-valence basis set with 6 Gaussian functions for core electrons and 3 for valence electrons, while the '*' signifies the inclusion of polarization functions.
2. The 6-31g* basis set is widely used for its balance between computational efficiency and accuracy, making it suitable for various molecular systems.
3. It is particularly effective for organic molecules and transition metal complexes, where polarization effects play a significant role in electronic properties.
4. This basis set can be extended to larger systems by combining it with other methods, such as density functional theory (DFT), to achieve even more precise results.
5. In practice, using 6-31g* can lead to better predictions for molecular geometries, vibrational frequencies, and reaction energies compared to using minimal basis sets.

Review Questions

• How does the inclusion of polarization functions in the 6-31g* basis set enhance the accuracy of quantum chemical calculations?
  • The inclusion of polarization functions in the 6-31g* basis set allows for a better representation of electron density distribution around atoms, especially when they are influenced by nearby atoms. This enhancement is crucial because it captures how electrons respond to molecular interactions and helps to accurately model molecular geometries and energies. As a result, calculations using this basis set yield improved predictions of properties like bond lengths and angles.
• Compare the 6-31g* basis set with minimal basis sets in terms of computational efficiency and accuracy for molecular modeling.
  • The 6-31g* basis set offers a significant improvement in accuracy over minimal basis sets by providing a more detailed description of electron distribution through its split-valence configuration and added polarization functions. While minimal basis sets might be faster due to fewer functions, they often fail to capture essential electron correlation effects. In contrast, 6-31g* strikes a balance, maintaining reasonable computational efficiency while providing reliable results for various chemical systems.
• Evaluate how the choice of a basis set like 6-31g* can impact the outcomes of quantum chemical calculations in research applications.
  • Choosing a basis set like 6-31g* can significantly impact research outcomes by influencing the accuracy of calculated molecular properties, reaction pathways, and energy barriers. A poorly chosen basis set may lead to incorrect predictions, which could misguide experimental efforts or theoretical interpretations. Therefore, researchers often select 6-31g* for its proven effectiveness in balancing precision with computational demands, ensuring that their studies yield credible and reproducible results across various applications in computational chemistry.

Related terms

Basis Set: A set of functions used to describe the electron cloud in quantum chemistry calculations, determining the accuracy and efficiency of computational models.

Gaussian-Type Orbitals: Mathematical functions that approximate atomic orbitals, commonly used in quantum chemistry due to their computational efficiency and suitability for molecular calculations.

Polarization Functions: Additional functions added to a basis set to account for the distortion of electron density in response to the presence of other atoms, improving the accuracy of molecular geometry and electronic structure calculations.