From chemistry-request {*at*} ccl.net Tue Mar  5 22:18:39 1991
Date: Tue, 05 Mar 91 20:43:52 CST
From: Jan Jensen <NU145752 \\at// VM1.NoDak.EDU>
Subject: Concepts vs. Accuracy??
To: chemistry -x- at -x- ccl.net
Organization: North Dakota Higher Education Computer Network
Status: R

In response to David Bernhold's thoughts, a quote from Levine's 'classical'
QUANTUM CHEMISTRY:

       Approximation of the helium ground-state wave function as a product
of hydrogenlike 1s orbitals with effective nuclear charge zeta [...] provides
a simple physical picture that is in accord with the usual chemical concepts;
however, this function does not give a very accurate value for the energy.
When we use a function like [...] with a hundred or so terms, we get an
extremely accurate wave function and energy, but we lose the simple physical
interpretation.  This is a general occurrence in quantum chemistry; "the
more accurate the calculations become the more the concepts tend to vanish
into thin air."[6]

    [6] R. S. Mulliken, J. Chem. Phys., 43, s2 (1965).

                               Levin, pg. 209


      Jan Jensen (NU145752 -A_T- NDSUVM1.EDU)
      Dept. of Chemistry
      North Dakota State University
      Fargo, ND 58105

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