NBO deletion procedure

NBO deletion procedure

Postby gbreton » Thu Dec 04, 2014 8:03 pm

Hi all,

I'm just starting with NBO and I'm somewhat confused on the proper procedure for deleting a weak intermolecular interaction. I am using the implementation of NBO 3.1 within Gaussian 09.

I have a weak ground state n ---> pi* (nitrogen lone pair to a carbonyl carbon) interaction for which I'd like to estimate the strength. I believe I am able to delete the interaction between these two atoms and then use the difference in energies between the systems with the interaction and without to determine the energetic contribution of the interaction.

Looking at the NBO 3.0 program manual, there are two types of deletion procedures that appear to be relevant:

i. (2) Deletion of specific Fock matrix elements.
ii. (8) Zeroing all delocalization from one molecular unit to another.

Which one of these will do what I desire? (hopefully this isn't too stupid of a question)

Also, I have been using DFT B3LYP/6-311+G(2d,p) calculations up to this point. Is it OK to use these for the NBO deletion procedure or do I need to look at HF? (I have read elsewhere that DFT calculations can be unreliable in NBO deletion procedures).

Finally, I would really like to re-optimize the structure following the deletion to see the effect on the molecule's conformation. Am I OK to do this?

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Re: NBO deletion procedure

Postby ericg » Thu Dec 04, 2014 10:10 pm

I encourage you to review the deletions tutorial on the NBO6 website (http://nbo6.chem.wisc.edu/tut_del.htm). The tutorial gives examples of various deletions and shows sample G09 input for geometry optimization with deletions.

Start by deleting specific elements of the Fock (or Kohn-Sham) matrix. It doesn't seem to me that you want to "zero delocalizations between molecular units." Different molecular units, here, refers to different molecules.

Deletions analysis with B3LYP is usually OK.

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Re: NBO deletion procedure

Postby gbreton » Fri Dec 05, 2014 7:15 am

Thank you, Eric! I reviewed the tutorial as you suggested, and it is indeed very helpful.
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Joined: Thu Dec 04, 2014 7:50 pm

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