Calculating Intramolecular interactions

Questions
#1

Hello there
What would be the best way to estimate the intramolecular interactions like - intramolecular hydrogen bonding, intramolecular pi-pi ineraction between two phenyl rings? Can this be done using fragment based methods? If yes I intend to use three fragments viz. - two interacting fragments and one linker fragment.
For example in this case I want to calculate the hydrogen bonding interaction between the two -OH groups while the carbon chain serves as a linker.

O          0.39987        2.94222       -0.26535
H          0.05893        2.05436       -0.50962
--
O          0.48122        0.30277       -0.77763
H          0.26106       -0.50005       -1.28451
--
C          2.33048       -1.00269        0.03771
C          1.89725        0.31533       -0.59009
C          2.28232        1.50669        0.29709
C          1.82204        2.84608       -0.29432
C          2.37905        4.02099        0.49639
H          3.41246       -1.03030        0.19825
H          2.05362       -1.84372       -0.60709
H          1.82714       -1.16382        0.99734
H          2.36243        0.42333       -1.57636
H          3.36962        1.51414        0.43813
H          1.81251        1.38060        1.28140
H          2.14344        2.92967       -1.33843
H          3.47320        4.02400        0.48819
H          2.03535        3.99216        1.53635
H          2.02481        4.96785        0.07455
#2

The ability to use linker fragments doesn’t exist in Q-Chem, to the best of my knowledge. (There are some procedures for this in the literature but my understanding is that results can be fairly sensitive to the details of how the linker fragment is embedded.) To use fragment-based methods that are in Q-Chem (e.g., SAPT and XSAPT-based approaches), you would need to actually separate the molecule into two and adding capping atoms, so that it becomes inter- rather than intramolecular. In a lot of cases I can still envision that you could obtain meaningful results in this way that would inform on the intramolecular interactions in which you are interested.

#3

Cn this be done using the extensive suit of NCI methods in multiwfn?

You might want to check out this paper:

Visualization Analysis of Weak Interactions in Chemical Systems
Tian Lu1 and Qinxue Chen2, Beijing Kein Research Center for Natural Sciences, Beijing, P. R. China
r 2024 Elsevier Inc. All rights reserved.

#4

NCI plots don’t provide any quantitative interaction energies, they are for visualization purposes only.