Dear Fitzerald,

The Wiberg bond orders (BOs) can easily be obtained for open-shell systems similar to closed-shell ones. As a very simple example, consider methane in cationic form (charge=+1 and multiplicity=2). First, optimize this system at, for instance, (U)B3LYP/6-31G(d) computational level followed by a frequency calculation to ensure there is not any imaginary frequency.

To obtain Wiberg bond orders, employ the following command line over the optimized structure:

ub3lyp/6-31G(d) pop=nboread

and use following keywords at the end of molecular specification part after a blank line:

$nbo bndidx $end

Your output file includes "Wiberg bond index matrix in the NAO basis" where the first "N A T U R A L  A T O M I C  O R B I T A L  A N D N A T U R A L  B O N D  O R B I T A L  A N A L Y S I S" is printed out. In the explained example, as expected, you should obtain a same BO of 0.731 between carbon (C1) and every hydrogen atoms (H2, H3, H4, and H5).

Note that while Alpha and Beta spins analyses are separately given in the next parts, you do not need such data for the purpose you are following.

I hope you find it helpful.

Sincerely,

Saeed

Dear Fitzerald Hujon,

One can calculate the bond order by employing the  NBO methodology. Considering water as an example the input should look like:

#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

And in the output you will come across the Wiberg bond index matrix as given below:

 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

Simply one has to give keywords like "POP=NBOREAD" followed by "$nbo bndidx $end".

All the best!

Hi Fitzerald,

You can compute bond order using NBO methodology which is within Gaussian 09 or in the new version of Gaussian16.  You are required to provide two keywords, one in the route section (POP=NBOREAD) and the other at the bottom of your input file ($nbo bndidx $end). The demonstration of the output file is shown by Mohsin Yousuf.

Best,

Ashim

Mr. Hujon,

It is obtained directly using:

- 'pop=nboread' to the route section, abd

- '$nbo dipole bndidx $end' to the 'molecule specification' one (after the coordinates).

Mr. Hujon,

There are several ways to get bond indices or say order. 

In case you are using G09:

The most popular one is NBO bond order, which can be obtained by typing this:

"pop=nboread" in the route line and then followed by "$nbo bndidx $end" in the end of your input.

If you are using external program with NBO 6.0, you just simply  need to add this

"pop=nbo6" 

Best,

Khidhir

Thank you very much...Really helpful ..@Saeedreza Emamian, 

@Mohsin Yousuf Lone .... I have tried that too... Thanks bro...

I am still using Guassian 09...So any idea what is the price of the latest one ? @Ashim Nandi

Thank you Sir @Khidhir Alhameedi ....right now its working properly...

I have another simple question just want to know how to take out the effective bond order/wiberg bond index from the output..as i have seen so far there are three values after calculating the NBO so which one to take ????? Thank you  

Hi,

Here is the link below for the pricing of G16

http://gaussian.com/pricing/

For Gaussian, you can add the following on the route line of your input file to get the .wfx file printed out:

density=current, output=wfx

(Also, you need to specify the desired name of your wfx file at the bottom of the Gaussian input file.)

Then use the free Chargemol program (http://ddec.sourceforge.net) to analyze the .wfx file. It will compute and print the net atomic charges, bond orders, and other information.

This algorithm for computing bond orders is more widely applicable than alternative methods. See the following paper for details: T. A. Manz, "Introducing DDEC6 atomic population analysis: part 3. Comprehensive method to compute bond orders," RSC Advances, 7 (2017) 45552-45581 (http://dx.doi.org/10.1039/C7RA07400J ).