Understanding 6-31G in Molecules: N2

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Discussion Overview

The discussion centers around the use of the 6-31G basis set in quantum chemistry, specifically in relation to the nitrogen molecule (N2) and its application to other molecules like hydrogen (H2). Participants explore the interpretation of the basis set notation and its implications for atomic orbitals.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant asks whether the 6-31G basis set refers to the total number of Gaussian functions for both atoms in a molecule or for each atom individually.
  • Another participant asserts that the Gaussian functions are used to approximate the atomic orbitals for each atom, implying that the basis set applies to each atom separately.
  • A further inquiry is made regarding the application of the 6-31G basis set to the hydrogen molecule, questioning how the basis set's components (6 for 1s and the 3+1 splitting) are utilized in this context.
  • A suggestion is made to consult the original publication on the basis set, which indicates that for hydrogen, a basis of two orbitals is employed, one being a contraction of three Gaussian-type orbitals (GTO) and the other a single GTO.

Areas of Agreement / Disagreement

Participants express differing views on the application of the 6-31G basis set, particularly regarding its interpretation for different atoms and molecules. The discussion remains unresolved with multiple perspectives presented.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the basis set's application and the specific definitions of the components within the 6-31G notation. The mathematical details of the basis set's construction and its implications for different types of atoms are not fully explored.

hiltac
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Hello !

When we say that we use a 6-31G for a molecule (ex: N2), it is this number of gaussian (6+3+1) for both of the atoms or for each atom ?
Thank you
 
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For each atom, obviously, as the gaussians are used to approximate the atomic orbitals of each atom.
 
And how can we explain to use a 6-31G basis set to study a molecule like H2 ? 6 gaussian for the 1s and what about the splitting in 3+1 ?
Thank you again
 

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