Subject: CCL: Re: Hund's rules

From: "Ajit J. Thakkar" <[email-masked]>
Date: Tue, 14 Nov 2000 08:21:20 -0400

Eric Scerri wrote:
>>Can Hund's rule of maximum multiplicity be derived from quantum mechanics
or is it still to be considered as the summary of experimental results?

Hund's rule of maximum multiplicity is not rigorous --- experimental cases
where it breaks down are rare but known.
Within the restricted Hartree-Fock approximation, the rule is exact and in
fact the energy difference can be shown to lie between  between multiples
of (positive) exchange integrals computed with the upper state orbitals and
the same quantity computed with the lower state orbitals. For more details
see:
Colpa, Mol Phys 28 (1974) 581; 
Colpa, Thakkar, Smith and Randle, Mol Phys 29 (1975) 1861. 

Ajit

-- 
Dr. Ajit J. Thakkar
Professor
Department of Chemistry                 Tel: 1-506-453-4629
University of New Brunswick             Fax: 1-506-453-4981
Fredericton, NB  E3B 6E2                 E-mail: [email-masked]
Canada                                  http://www.unb.ca/chem/ajit/