Subject: Re: CCL:Molden Laplacian Plot options.

From: Victor Lua~na <[email-masked]>
Date: Wed, 30 Apr 2003 12:48:19 +0200 (METDST)

> From: Stephen Cooke <[email-masked]>
> Subject: CCL:Molden Laplacian Plot options.
>
> We have an interest in our laboratory in examining the bonding in rare gas 
> containing molecules through experiment.  Accordingly we have begun 
> supplementing our experimental work with theoretical calculations and in 
> particular producing electron density plots of our molecules and also 
> examing the laplacian plots, all using Molden.
>
> Of increasing interest is the Laplacian.  Molden has 
> 4 plot options for the laplacian, i'm sure many of you will know 
> these are:  Euclid, 3D, 3D-X and Space.  [.......]
>
> My question is how should one interpret the "Space plot" of the Laplacian?
> I have examined the online documentation and have not been successful in 
> finding any help.

Literal answer: molden "space plot" are isosurfaces of the 3D function.
The program asks you for a value of the function and the plots as a
collection of planes the aspect of the L(\vec{r}) = constant surface.
Of particular interest is the L(\vec{r})=0 surface, called "reaction
surface" after R. F. W. Bader.

If you want to examine the isodensity or isolaplacian surfaces of a
number of molecules you should consider leaving molden and using
"molekel" or "gopenmol" instead. Both viewers provide you a quite
improved interaction with the surface and they are faster by orders
of magnitude.

   molekel:   http://www.cscs.ch/molekel/
   gopenmol:  http://www.csc.fi/gopenmol/

On the other hand, you might be interested in the chemical information
contained in the laplacian. In that case you could check a corpus of
relevant literature related to the Quantum Theory of Atoms in Molecules.
For instance, the critical points in the laplacian can be shown to
provide a qualitative and quantitative support to Gillespie's VSEPR
model. The negative and positive isosurfaces of the laplacian provide a
map of the nucleophile and electrophile regions of the molecule. ... A
collection of beatiful pictures of the laplacian can be found in the web
pages by R.F.W. Bader and also on the web pages by Creon Levitt. Some
relevant articles can be found by looking to the recent work (about five
years to start with) by Bader, Gillespie or Bernard Silvi.

   Bader:       http://www.chemistry.mcmaster.ca/faculty/bader/aim/
   Levitt:      http://people.nas.nasa.gov/~creon/home.html
                It appears to be unaccesible for me right now
                and google didn't provide an alternative site.
   Silvi:       http://www.lct.jussieu.fr/silvi/
   Gillespie:   http://www.chemistry.mcmaster.ca/faculty/gillespie/

Finally, PLA. Popelier and E. Espinosa have been quite active in the
analysis of intermolecular bonding through the characterization of
the electron density, laplacian and related properties. You could check
their work as it might provide you relevant ideas to your problem.

   Popelier:    http://www2.umist.ac.uk/chemistry/contact/staff/popelier.htm
   Espinosa:    http://www.u-bourgogne.fr/LIMSAG/publicat/espinosa.htm

Hope this helps you. Best regards,
                                   Victor Lua~na