Subject: Re: CCL:Correction of Koopmans ionization potentials

From: Russell D Johnson III <russell.johnson ~~ nist.gov>
Date: Mon, 09 May 2005 14:07:00 -0400

Hello,

  The NIST CCCBDB (Computational Chemistry Comparison and Benchmark Database) has some experiment vs theory comparisons of Koopman's ionization potentials. It provides differences rather than ratios, but a cursory glance makes it look like a general multiplication factor will not do very well.

The CCCBDB is online at:
http://srdata.nist.gov/cccbdb

See section IV.E.3 and try entering C?H? to get a list of hydrocarbons.  After selecting some or all the molecules from the list choose the table cell for HF/6-31G*. The differences range from -0.5 to 1.7, which doesn't look easy to correct using a scale factor. Even if you choose a subset, such as molecules with a carbon-carbon triple bond, there is still a spread.

At 09:58 AM 2005-05-09, you wrote:
>Dear colleagues, 
> 
>I heard that the Koopmans ionization potentials (HF method) can be
>corrected by a multiplication factor of about 0.92, but I am not sure it
>is true. 
>Could anybody provide me some references to the corrections of Koopmans
>ionization potentials? 

Dr. Russell D. Johnson III
Research Chemist
National Institute of Standards and Technology
Computational Chemistry Group
100 Bureau Drive, Stop 8380
Gaithersburg, MD 20899-8380
voice: 301+975-2513 fax:301+869-4020
email: russell.johnson ~~ nist.gov