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Anjali Ganai

Member

Registered: 2022-08-17

Posts: 13

Second Order Perturbation Theory Analysis using Gaussian Software

Hello,

I have carried out the second order perturbation analysis and a small section of the output is (showing the involved NBOs and Stabilization Energies):

21. BD(1) C 25-H 28       /121. LP*(7)Fe 30    9.06
21. BD(1) C 25-H 28       /122. LP*(8)Fe 30    11.23

Now NBO No. 121 and 122 are almost pure P orbitals as can be seen from below
121. (0.09383) LP*(7)Fe 30     s(1.96%)p49.61(97.4%)d 0.30(0.60%)f 0.00(0.00%)
122. (0.08905) LP*(8)Fe 30     s(1.16%)p84.81(98.31%)d 0.46(0.53%)f 0.00(0.00%)

My question is which of the two NBO(121 or 122 or both) should I consider? Do I need to add both values of stabilization energies (11.23+9.06) to make comparison with other systems?

Regards,
Anjali

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,631

Website

Re: Second Order Perturbation Theory Analysis using Gaussian Software

Dear Anjali,

Both of them should be considered. However, the two values cannot be added together, there will be an overcounting problem.

Best,

Tian

Anjali Ganai

Member

Registered: 2022-08-17

Posts: 13

Re: Second Order Perturbation Theory Analysis using Gaussian Software

Then how am I supposed to make comparison with other system since the other system also has a stabilization energy of 18.87 and 0.80 respectively for the same donor-acceptor pairs.
Added to this there are contributions involving s-orbital.
Here am giving an example of how the systems differ in their stabilization energy values.
System 1
donor-->p-orbital = 11.23
donor-->p-orbital = 9.06
donor-->s-orbital= 4.83

System2

donor-->p-orbital = 18.87
donor-->p-orbital = 0.80
donor-->s-orbital= 15.06

The donor orbital is the same in each case. It is a C-H sigma bond.

Last edited by Anjali Ganai (2023-06-15 11:43:02)

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,631

Website

Re: Second Order Perturbation Theory Analysis using Gaussian Software

System2 has stronger overall hyperconjugation

Anjali Ganai

Member

Registered: 2022-08-17

Posts: 13

Re: Second Order Perturbation Theory Analysis using Gaussian Software

Thanks a lot.

Regards,
Anjali