Subject: Summary of How to calculate Bond Orders.

From: [email-masked] (Somsak Tonmunphean)
Date: Tue, 17 Dec 1996 10:40:31 +0000 (WET)

Dear Netters,
	A few days ago, I asked the question "How to calculate bond order 
of molecule ?", I have received some good anwering mails and here is my 
summary.  
	Thank you very much to the following persons who gave the great
answers.
	 Robert Ponec ([email-masked])
	 Dr.Stephan Irle ([email-masked])             
	 Dr. Jeff Gosper ([email-masked])
	 John R. Nash ([email-masked])
	 Dr. Joel Polowin ([email-masked])
	 Elmar Gerwalin ([email-masked])
	 Alan Shuterman ([email-masked])
	 Dr. Tapas Kar ([email-masked])
	 Dr. Damir Kovacek ([email-masked])

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From: Robert Ponec ([email-masked])

There is still some discussion about how to define bond order. The   
situation is clearer at SCF level where the generally accepted definition   
of bond order (sometimes called bon index) is that proposed some years   
ago by Wiberg. His bond indeces are sometimes referred to as Wiberg   
indices). What MOPAC calculates using BOND keyword is just this type of   
index. It has the advantage that his values for single bonds are close to   
1, dor double bonds close to 2 etc and for nonbonded atoms they are   
usually negligible and so they correspond well to the classical   
understanding of bond multiplicity. The Wiberg indices were originally   
defined for orthogonal basis sets ( i.e. they are straightforwardly   
applicabl;e at semiempirical level) but the extension to ab initio level   
was proposed by Mayer. If you are satisfied with SCF level only, it is   
best to use Wiberg or Mayer indices. A bit more complex situation is for   
correlated wave functions where the definition od bond index is still the   
subject of discussion. Since I have been working in this field quite   
recently, I can send you a reprint of my recent study on this subject.   
 You can find all the references to Wiberg and Mayer works there. Let me   
please know whether you are interested in it.

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From: [email-masked] (Stephan Irle)

You should have asked me. I've implemented Mayer's bond orders
into G92, and you can have it, of course with the references.

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From: [email-masked] (Joel Polowin)

It is not possible to calculate bond orders automatically with HyperChem, 
but they can be calculated manually from the density matrices, which can 
be printed in a log file.  The bond order between atoms A and B is the sum 
of the squares of the elements in the density matrix with rows for atom A's 
orbitals and columns for atom B's orbitals, or vice versa.  If you are 
doing UHF calculations, you must add the elements of the alpha and beta 
matrices together before squaring.  I tried this for C2H4 as model-built, 
with an AM1 single-point calculation, and got a C--C bond order of 2.0004.

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From: "John R. Nash" <[email-masked]>

F. Weinhold's Natural Bond Order (NBO) calculation available with G92 (and
G94) will calculate bond orders (and do decomposition of bonds into "ionic"
and "covalent" parts if requested).  Check the manual for details, but at
its simplest, you just put "POP=NBO" in the route card and $NBO $END at the
end of the input file.  This gives the default NBO analysis, including bond
orders.

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From: Jeffrey J Gosper <[email-masked]>

MOPAC can calculate bond orders (using the BONDS keyword). We are currently 
working on an Windows program that will take XYZ files, run MOPAC, and 
produce an 'extended' XYZ file that contain bond connectivities and orders 
which can be viewed in Re_View2.

Until this is finished you can look at the degrees of bonding table in the 
MOPAC output.
 
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From: Elmar Gerwalin <[email-masked]>

In Gaussian you can calculate Bond orders very easily:
Mulliken Overlap Populations are calculated by default.
Better is the NBO-Program Package that mostly comes along with Gaussian (all
Versions up to G94)
Please refer to the Gaussian Homepage, your Software ADministrator or search the
Web for NBO (Natural Bond Order Analysis). 
If I find a link to Gaussian/NBO in my own Bookmarks, I will tell you.

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From: "Tapas Kar, Ph.D, Asst. Scientist" <[email-masked]>

Here is some important references for bond order calculations:
J. Chem.Education 65(1988)674, J. Mol.Structure(Theochem)209(1990)45,
Chem.Phys.lett.173(1990),569 and 192(1992)14.
You have to modify l601.F of gaussian92 to add bond order calculation
because it is not available as standard calculation in G92. It is a
simple program and you can add few lines in l601.F.

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>From Dr. Damir Kovacek <[email-masked]>

GAMESS (US version) can calculate total bond orders and I have programs 
that can extract pi-bond orders from GAMESS and MOPAC output. If you are 
interested just send e-mail.

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