Subject: Concepts vs. Accuracy??

From: Jan Jensen <[email-masked]>
Date: Tue, 05 Mar 91 20:43:52 CST

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 ([email-masked])
      Dept. of Chemistry
      North Dakota State University
      Fargo, ND 58105

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