Subject: Bond orders

From: "Hongbin Du" <[email-masked]>
Date: Fri, 11 Aug 2000 15:13:51 -0400

Dear CCLers,

Using Gaussian, NBO, AIMPAC etc., one can obtain several kinds of bond
orders: AIM bond order, Wiberg Bond order, overlap-weighted NAO bond order,
NLMO/NPA bond order (bo). Here are the questions:

(1) Which is 'the best' to describe the bonding in molecules? In our recent
study, only AIM bond order had the 'right' number (i.e. b.o. ~ 1.4 by
comparison of the electron densities at the bond critical points with the
standard compounds, Classical Lewis acid-base theory yields a bo of 1.5,
while NBO analyses gave various bo around 1.0). Could somebody recommend any
reference for their comparison?

(2) What is the physical meaning for the negative NBO bond orders in the ?
For example:
    Atom-Atom Net Linear NLMO/NPA Bond Orders:
      Atom    1       2       3       ...
      ---- ------  ------  ------  ...
    1.  C  0.0000  0.8174  0.7960  ...
    2.  N  0.8174  0.0000 -0.0104 ...
    3.  H  0.7960 -0.0104  0.0000 ...
     ...

Thank you,
Hongbin