In gaussian, NBO analysis is done but I am not confidently able to decide the number of interacting molecules under the heading of Second Order Perturbation Theory Analysis of Fock Matrix in NBO Basis.
Please help if possible
How to decide the most interacting orbitals in these three files i.e within unit1 , from unit 1 to 2 and from unit 2 to 1.
I will be grateful if anyone could help and clarify....
Hello,
in a SOPT analysis of the interactions between two molecules or ions you typically look for the interaction between a nonbonding pairs of electrons (a LP) located on the donor and a virtual (empty) natural orbital (BD*) on the acceptor. The column E lists the interaction energies (in kcal mol-1). Please note that also intramolecular CT interactions are possible and will be included in the interactions occurring within a fragment. It is also worth noting that the orbitals listed in this section are NBOs and not KS-MOs.
I hope this may help.
Hello sir,
My question particulary pertains to the NBO analysis.
I will be happy if you can help.....waiting for your reply sir
Dear Asheesh,
your question apparently regards Second Order Perturbation Theory (SOPT) Analysis and only indirectly the more general topic of Natural Bond Orbital (NBO) analysis.
Therefore - coming back to the subject - you will notice that the largest transfers occur within fragment1 (C-C BD --> C-C BD*, pointing to a a pi-electron delocalization accounting for about 20 kcal mol-1).
I cannot comment anymore without a drawing and a labelling scheme of your molecule(s) and the unit composition.
You should check this in order to understand where the involved carbons are located in your compound. A graphic program (Gaussview, molden, avogadro, just to cite few examples) may help you do this.
Regards,
M.
Sir can I send you the exact file so that, sir you can help me in a better way...Here I am attaching the file below. Please download it and kindly help....
Dear Asheesh,
In my opinion an analysis of the output file does not show any significant interaction (from unit1 to unit2 and vice versa) between the two fragments, that indeed are quite far (> 3 Å).
Dear sir,
So, In your opinion sir, if the gap is more than 3 angstrom, then is it so that one should not do NBO analysis..
Dear Asheesh,
it depends on the (possibly) interacting synthons. In your case, very weak interactions could be present, and possibly your computational setup is not the best. You might try to improve the functional by passing to one including Grimme's dispersion corrections and you may want to augment your BS with diffuse functions. You will have to reoptimized your geometry with the new setup, but you can use the previous calculations' chk to guess the electron density.
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