I am trying to perform nbo calculations on an optimized structure using Gaussian software. I've included my input file as well as abbreviated NBO orbital interaction output. The separation of this molecule into unit 1 and unit 2 excludes orbital interactions of interest. Is there a way to force NBO calculations on a single molecular unit that includes all of the atoms in the structure?
%chk=popfull.chk
# pop=nbo def2tzvp m062x
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0 1
C 1.95142900 1.26670400 -0.64686300
C 1.49877700 1.25230100 0.81204400
C 0.68871800 -0.00064100 1.14730100
C 1.49928100 -1.25293900 0.81112200
C 1.95190300 -1.26607100 -0.64780600
C 2.73279200 0.00058800 -0.99641200
H 0.42464900 -0.00107800 2.20608600
H 2.39583300 1.26350300 1.44686400
H 0.94295000 2.16218600 1.04824300
H 1.07322900 1.34303900 -1.30171200
H 2.56075300 2.15028700 -0.84583400
H 2.39634600 -1.26420000 1.44592400
H 0.94384400 -2.16323700 1.04663700
H 2.56153300 -2.14928500 -0.84747900
H 1.07368200 -1.34221000 -1.30262700
H 3.67138100 0.00054400 -0.43267600
H 3.00144000 0.00105300 -2.05435600
F -2.91217100 0.00014000 -0.85547800
Cd -1.18278100 -0.00003100 0.09195700
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Donor NBO (i) Acceptor NBO (j) kcal/mol a.u. a.u.
===================================================================================================
within unit 1
1. BD ( 1) C 1 - C 2 /172. RY*( 1) C 6 0.62 2.04 0.032
from unit 1 to unit 2
10. BD ( 1) C 3 -Cd 19 /253. RY*( 1) F 18 1.42 1.98 0.048
from unit 2 to unit 1
25. CR ( 1) F 18 / 39. LP*( 6)Cd 19 2.78 25.22 0.239
within unit 2
33. LP ( 4) F 18 /257. RY*( 5) F 18 0.53 3.03 0.037
Dear Kyle Fisch ,
In principle, you can force Gaussian to use the Lewis structure coming from the connectivity using the geom=connectivity keyword (drawing the bonds you need to specify, the bond order does not matter) alongside iop(6/74=1).
But I have to add that I have run a test with the water dimer and, if I force it to a single molecular unit, some strange interactions arise. I have attached the two output files (one specifying the connectivity, one not) as text files, so you can compare. What I mean is that proceed with caution if you enforce a single molecular unit when interpreting the results.
Hope you find it helpful
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