Re: CCL:Bond order in gaussian

Ding,

WebMO (www.webmo.net) is a very useful tool for learning how to construct input files to perform particular tasks.

For example, to calculate bond order in Gaussian, build a test molecule, choose Gaussian, request a "Bond Orders" calculation, and choose to "Preview Input File".  For H2O, this might result in:

#N HF/3-21G SP POP=NBOREAD

H2O

0 1
O
H 1 B1
H 1 B2 2 A1

A1 109.47122
B1 1.0500000
B2 1.0500000

$nbo bndidx $end
from which one learns that the important keywords are "POP=NBOREAD" followed by "$nbo bndidx $end".  The resulting output includes

Wiberg bond index matrix in
 the NAO
 basis:                                   
      Atom   
 1      
 2       3
      ---- ------  ------  ------
    1.  O  0.0000  0.8146  0.8146
    2.  H  0.8146  0.0000  0.0019
    3.  H  0.8146  0.0019  0.0000

What you have listed are the Natural Bonding Orbitals, which are "localized orbitals" that look very similar to "organic chemistry bonds", i.e., BD=Bond, CR=core, LP=lone pair, RY=Rydberg, *=excited/antibonding, etc.

Will Polik

At 09:21 PM 11/4/2003, Ding Xunlei wrote:

I am try to do a bond order analysis with G98.
        Here is my test with O2 molecule. 

#B3LYP/6-31G opt pop=(NBO,Bonding)

HF

0 3
O   0.00 0.00 0.000000
O   0.00 0.00 1.200000

The last lines of the output file is below, and I don't think it is right.
How can I read the table correctly?     And what the LP,RY* stand for?

    Thank you very much for your help!!!!!!!!!!!!!!!!!  
                
 Natural Bond Orbitals (Summary):

                                                     Principal Delocalizations
           NBO              Occupancy    Energy      (geminal,vicinal,remote)
 ===============================================================================
        Molecular unit  1  (O2)
   1. BD ( 1) O 1- O 2       1.00000    -1.03224
   2. BD ( 2) O 1- O 2       1.00000    -0.45369
   3. BD ( 3) O 1- O 2       1.00000    -0.45369
   4. CR ( 1) O 1            0.99997   -19.14436    12(v)
   5. CR ( 1) O 2            0.99997   -19.14436    8(v)
   6. LP ( 1) O 1            0.99984    -0.87950    12(v)
   7. LP ( 1) O 2            0.99984    -0.87950    8(v)
   8. RY*( 1) O 1            0.00019     0.95747
   9. RY*( 2) O 1            0.00000     0.88719
  10. RY*( 3) O 1            0.00000     0.88719
  11. RY*( 4) O 1            0.00000     1.07773
  12. RY*( 1) O 2            0.00019     0.95747
  13. RY*( 2) O 2            0.00000     0.88719
  14. RY*( 3) O 2            0.00000     0.88719
  15. RY*( 4) O 2            0.00000     1.07773
  16. BD*( 1) O 1- O 2       0.00000     0.26370
  17. BD*( 2) O 1- O 2       0.00000    -0.13403
  18. BD*( 3) O 1- O 2       0.00000    -0.13403
       -------------------------------
              Total Lewis    6.99962  ( 99.9946)
        Valence non-Lewis    0.00000  (  0.0000)
        Rydberg non-Lewis    0.00038  (  0.0054)
       -------------------------------
            Total unit  1    7.00000  (100.0000)
           Charge unit  1    1.00000
        
        

                                
Ding Xunlei
2003-11-05
______________________________________________
Ding Xunlei, Ph.D. Candidate
Open Laboratory of Bond Selective Chemistry
University of Science & Technology of China
Hefei, Anhui 230026, P.R.China
Tel.: 0086-551-3603418
Fax.: 0086-551-3602969
E-mail: dxl{at}mail.ustc.edu.cn
http://www.bsc.ustc.edu.cn/~dxl