question about the CHOOSE keyword in NBO



Hi

I have a doubt about the operation of analysis NBO searching the best Lewis structure.

The description of Lewis of a certain molecule gives me a little strange result. Then I repeat the calculation on the same molecule with the option CHOOSE (DIRECTED NBO SEARCH) choosing a more "normal" structure of Lewis and in this second calculation I obtain a smaller Dev and smaller Total non-Lewis.

This is normal? Because I thought that in the process of optimization NBO the structure with a smaller amount of non-Lewis and a smaller Dev would have to be obtained.

Thanks

 

*******************************************
Without CHOOSE (free NBO search):
*******************************************
NATURAL BOND ORBITAL ANALYSIS:
 
Cycle Thresh. Lewis Non-Lewis CR BD 3C LP (L) (NL) Dev
=============================================================================
1(1) 1.90 33.82805 2.17195 5 11 0 2 2 3 0.59
2(2) 1.90 33.82805 2.17195 5 11 0 2 2 3 0.59
3(1) 1.80 34.34760 1.65240 5 12 0 1 2 3 0.59
4(2) 1.80 33.42460 2.57540 5 13 0 0 4 5 0.59
.
.
38(9) 1.50 34.21710 1.78290 5 11 0 2 1 3 0.37
39(1) 1.70 34.54664 1.45336 5 12 0 1 1 3 0.37
-----------------------------------------------------------------------------
Total non-Lewis 1.45336 ( 4.037% of 36)
--------------------------------------------------------
 
 
*******************
With CHOOSE:
*******************
NATURAL BOND ORBITAL ANALYSIS:
 
Cycle Thresh. Lewis Non-Lewis CR BD 3C LP (L) (NL) Dev
=============================================================================
1(1) 1.90 34.72964 1.27036 5 12 0 1 3 3 0.34
-----------------------------------------------------------------------------
 
Total non-Lewis 1.27036 ( 3.529% of 36)