Spartan tip – Natural Bond Orbitals

Parts of Weinhold’s Natural Population Analysis (NAO, NBO, but not NHO, NRT, perturbation calculations, etc.) have been part of Spartan from the very beginning, but the instructions for accessing this analysis keeps changing. Here is my understanding of what parts you can access in Spartan’14 and how to get them:

  • Natural atomic charges – By default, all successful quantum calculations (HF, DFT, etc.) in Spartan’14 are followed automatically by calculations of electrostatic, Mulliken, and Natural charges, i.e., charges based on Weinhold’s Natural Atomic Orbitals (NAO). The easiest way to see these charges is to click Display: Properties and then click the atom of interest.
    • Another way to see charges is to click Model: Configure and then select the charge of interest. All of the charges will be displayed on the model simultaneously.
    • Yet another way to see charges is to click Setup: Calculations and then click the Print: Charges & Bond Orders. This will add a list of Natural charges to the text output (Display: Output).
  • Natural Atomic Orbital (NAO) populations – An atom’s Natural charge can be parsed into NAO populations. Normally, one expects large populations for compact low-energy orbitals (labeled “MIN”) and vanishingly small populations for diffuse high-energy orbitals (labeled “RYD”). A list of these orbitals and their populations can be generated in the text output by entering the keywords NBO PROPPRINTLEV=2 in Setup: Calculations.
  • Natural Bond Orbital (NBO) definitions and populations – NBO usually correspond to the bond orbitals one might anticipate by looking at a molecule’s Lewis structure, e.g., the NBO of methane include 4 CH sigma bonding orbitals. A list of these orbitals (broken down into NAO contributions from each atom) and their populations can be generated in the text output by entering the keywords NBO PROPPRINTLEV=2 in Setup: Calculations.
  • Natural Bond Orders – A list of bonds and numerical Natural bond orders can be generated in the text output by entering the keywords NBO PROPPRINTLEV=2 in Setup: Calculations.
  • Controlling the output – More control over the appearance of the NBO can be achieved by combining PROPPRINTLEV=2 with one of the following keywords: NBO=NORMAL or NBO=IONIC or NBO=3C. However, if one really wants to access the full sophistication of NBO analysis, it probably makes better sense to use the NBO6 program itself.
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