Subject: Summary - Information about MEDLA

From: [email-masked] (Bill Laidig)
Date: Sat, 16 Sep 1995 14:18:21 -0400

A week or so ago I sent the following post:

>All,
>
>In a recent C&E News article an approximate electronic structure method
>called MEDLA by Prof. P.G. Mezey was discussed. I was asked by my boss if
>this really was the greatest invention since sliced bread as the article
>implied. Since I am not familar with this method I was wondering if any
>of you have thoughts on the subject. Also, is this technique similar
>to Yang's divide-and-conquer approach? I will summarize to the list if
>I get any responses. Bill

I only received one response here it is:

*******************************************************************************
   Hi ;

   I don't know much about MEDLA but my understanding is that MEDLA
is QUITE DIFFERENT from the divide-and-conquer method.  MEDLA is a
procedure to "flesh out" a nuclei configuration with an approximate
electron density without doing a first-principles calculations: instead,
it assembles in "some way" fragment densities that were previously
calculated and saved in a library.  Apparently this density is accurate
enough to get reliable Molecular Electrosatic Potential, and this (MEP) is
a key physical quantity for molecules of biological interests.  But I
would GUESS that the total energy probably cannot be obtained to any
useful degree of accuracy using only the MEDLA density as input because:

  (1) the best "density-only" kinetic energy functionals are still
not very good, which is one reason why people still do SCF Kohn-Sham
calculations;

  (2) small differences between trial and converged SCF density
can give significant errors on total energy differences.

    Still, using a MEDLA input density (which should be at least "fairly
accurate") together with a one-iteration-only Harris functional calculation
might be a way to get accurate total energies (nearly as accurate as
a full blown SCF calculation?) at relatively low computational cost
(say, roughly 20 times less than a conventional SCF calculation requiring
20 iterations).  If that's the case, MEDLA could be the greatest invention
since ... the muffin tin potential.

    Rene Fournier.
 |-------------------------------|-----------------------------|
 | Rene Fournier                 |  [email-masked]  |
 | Department of Physics         |  [email-masked]   |
 | University of Nevada          |  phone : (702) 895 1706     |
 | Las Vegas, NV 89154-4002 USA  |  FAX   : (702) 895 0804     |
 |-------------------------------|-----------------------------|

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*     Bill Laidig                                                            *
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