Subject: KCl CLUSTERS ANSWERS SUMMARY

From: Errol Lewars <[email-masked]>
Date: Sat, 29 Jan 2000 15:57:27 -0500

2000 Jan 29

Hello, here is the summary of answers to my query about KCl clusters.
Thanks very much to all who replied. I hope I included all responses.
[#1--#9, below]

  E. Lewars
==============
THE QUESTION

2000 Jan 18

Hello,

        A colleague in my Department has looked at the mass spectra of
clusters
consisting of one K+ surrounded by several KCl molecules (or ion-pairs,
if you prefer), and clusters of one Cl- surounded by several KCl
molecules (this latter with _negative_-ion mass spec). I think these can
be thought of as K+ solvated with KCl, and Cl- solvated with KCl. He's
found that some clusters are particularly prominent, as if there were
certain magic numbers of stable KCl "solvent" molecules (a bit
reminiscent of prominent clusters in Cn mixtures, where a big C60 peak
led to the hypothesis of buckminsterfullerene).

QUESTION:
Is there a program that will handle from a few up to about 100 KCl
molecules plus a K+ or Cl- ion? Please note that these clusters may not
be simple periodic systems like a KCl crystal. I don't know if they can
even be viewed as a doped KCl crystal. We are looking for a
rationalization of the fact that clusters of certain sizes seem to be
favored.

  Thanks

    E. Lewars
==========
=========
THE ANSWERS

#1
Dear E. Lewars,

Regarding your question about clusters made up from ionic salts:

I have been personally involved in the theoretical modelling of such
clusters
with an ab initio yet quite simple methodology. Rather than explaining
myself
in this mail, I think it is better if you have a look at our recent
papers:

"Theoretical Study of Small (NaI)n Clusters"
Andres Aguado et al. J. Phys. Chem. B 101, 5944-5950 (1997).

"Structural and Electronic Properties of Smalll Neutral (MgO)n Clusters"
Eduardo de la Puente et al. Phys. Rev. B 56, 7606-7614 (1997).

"Structure and Bonding in Small Neutral Alcali Halide Clusters"
Andres Aguado et al. Phys. Rev. B 56, 15353-15360 (1997).

"Ab initio Calculations of Structures and Stabilities of (NaI)nNa+ and
 (CsI)nCs+ Cluster Ions"
Andres Aguado et al. Phys. Rev. B 58, 9972-9979 (1998).

"Structures and Stabilities of Doubly-Charged (MgO)nMg2+ (n=1-29)
 Cluster Ions"
Andres Aguado et al. J. Chem. Phys. 110, 4788-4796 (1999).

The two last ones are perhaps the most interesting to you as the
clusters
considered have the composition with an extra ion you mention in your
mail.
In brief, the main aproximation of the model (that makes it faster than
others
electronic-structure methods) is the neglect of the polarization forces.
This
can be a quite reasonable assumption for alkali halides if you don't
look for
very thin details. However, it is not a good assumption at all for
oxides, so
in the last paper we included such terms semiempirically.

The method we employ is called the PI method, and is useful for studying
ionic materials, both crystals (pure or doped) and clusters. You'll find
references to the original works with the PI model in our works. If the
field of doped crystals is interesting to you, you may have a look to
the
following work:

"Lattice Distortions around a Tl+ Impurity in NaI:Tl+ and CsI:Tl+
Scintillators:
An ab initio study involving Large Active Clusters"
Andres Aguado et al. Phys. Rev. B 58, 11964-11969 (1998).

"Calculations of the Band Gap Energy and Study of Cross Luminescence
in Alkaline-Earth Dihalide Crystals"
Andres Aguado et al. J. Phys. Soc. Jpn. 68, 2829 (1999).

Hope this helps. The method is quite able to manage with clusters of
about
100 atoms if you do not pretend to perform molecular dynamics
simulations,
but just static calculations. To perform dynamical calculations, tou
should
turn to parameterized pair potential models, from which those of Paul
Madden
are the most accurate known to me up to date. 

Best regards,

Andres Aguado.

--Date: 
        Tue, 18 Jan 2000 08:19:11 +0100
  From: 
        Andres Aguado <[email-masked]>
=========
#2
This has already been done, at least for (NaCl)_n: cf. the Cambridge
Cluster
Database; in this case:
   http://brian.ch.cam.ac.uk/~jon/structures/NaCl.html
>From a suitable plot of the cohesive energies given there, you should be
able to get a first idea about "magic numbers", up to and including
n=35.

For programs that can handle this type of problem, given a suitable
model potential, cf. the work of the CCD authors (Doye, Wales, et al.),
or alternatively my work, cf. 
   http://www.theochem.uni-stuttgart.de/~hartke
If the above mentioned NaCl results are not yet sufficient for you, and
if
you want to go beyond n=35, I would be interested in a collaboration on
this
project. Just contact me at
   [email-masked]

In contrast to the CCD authors, I have succeeded in treating the global
cluster
geometry optimization problem also on the DFT and ab-initio levels, see
the 
refs. given on my home page above (although, obviously, this can be done
only for considerably smaller systems...). 
I know of only one other group attempting a similar approach, albeit not
for
geometry optimization but for MD: Novaro et al., J.Chem.Phys. 109 (1998)
2176.

Bernd Hartke

-- 
PD Dr. Bernd Hartke               e-mail:
[email-masked]
Dep. of Theoretical Chemistry     e-mail:
[email-masked]
University of Stuttgart          
http://www.theochem.uni-stuttgart.de/~hartke
Pfaffenwaldring 55                Phone: +49-711-685-4409
70569 Stuttgart                   FAX:   +49-711-685-4442
GERMANY
=============
#3
Just look at my web page, the address is below.

On Jan 20, 12:07pm, Errol Lewars wrote:
> Subject: Re: Clusters
> Donald E. Williams wrote:
> >
> > Mpa/mpg can handle cluster energy minimization without assuming any
symmetry.
> >  You have to provide the nonbonded energy functions.
> >
> > --
> > Dr. Donald E. Williams          email:[email-masked]
> > Department of Chemistry         http://www.louisville.edu/~dewill01
> > University of Louisville        phone:502-852-5975
> > Louisville, KY 40292            fax:  502-852-8149
>
> ====
> Hello,
>
> Thank you for your reply. I'll see if I can track down mpa/mpg, which i
> guess are molecular mechanics-type (force field) programs.
>
> EL
> ====
>-- End of excerpt from Errol Lewars

-- 
Dr. Donald E. Williams          email:[email-masked]
Department of Chemistry         http://www.louisville.edu/~dewill01
University of Louisville        phone:502-852-5975
Louisville, KY 40292            fax:  502-852-8149
======
#4
Before spending a lot of time on this calculation, which would be
interesting, and may I think already be in the literature, note that
these
magic clusters appear to be a kinetic rather than thermodynamic effect
in
the ms of alkali halide cluster ions, both +ve and -ve mass spectra.
They
are instrument geometry and size and accelerating voltage dependant in
magnetic instruments --- i.e. deppend on time available for
equilibration.

Prof. Jack M. Miller,
Associate Vice-President, Research and
Dean of Graduate Studies,
Professor of Chemistry,
Brock University,
St. Catharines, Ont.,
Canada, L2S 3A1.

Phone (905) 688 5550, ext 3789
FAX   (905) 682 2277
e-mail [email-masked]
http://chemiris.labs.brocku.ca/~chemweb/faculty/miller/
=====
#5
I cannot provide immediate information regarding calc-programs, but
these
magic numbers effects are well-known for metallic clusters (of
comparable
size). You might look up what these people are using to predict/explain
them (e.g. for Na_n or K_n).

-- Jochen
        Heinrich-Heine-Universität, Institut für Physikalische Chemie I
        Universitätsstr. 1, Geb. 26.43.02.29, 40225 Düsseldorf, Germany
phone 02118113681 fax 02118115195  -- 
www-public.rz.uni-duesseldorf.de/~jochen
[email-masked] -- [email-masked] --
[email-masked]
==========
#6
Errol,

What kind of simulation did you have in mind? Classical with empirical
interactions? Gas-phase? I simulated gas-phase KCl clusters classically
using a Born-Mayer potential, and I imagine simply adding one more 
ion would be trivial. However, I don't know if this empirical potential
would work with a net charge or not. 

I unfortunately cannot get my hands on my old papers about KCl clusters
(both neutral and charged). If memory of the literature serves, there
will
be several types of "magic" clusters with rocksalt structure, such as
3x3x3
or 5x5x5 arrangements of K and Cl in a cubic shape (and many other
possible rectangular geometries) similar to the 2x2x2 and 4x4x4
magic structures for neutral clusters. For anything over about 
10 ions, rocksalt structures should always give you the most 
stable energy, even for singly-charged clusters. 

These experiments remind me of similar, but more complicated,
simulations of (KCl)_n + e-  using quantum path-integral methods
to simulate the thermodynamic behavior of the free electron. 
Once again, rocksalt structures were often observed, with the 
electron occupying a "negative ion vacancy" (like an F-color center).
Sometimes the electron was distributed on the surface, however.

Let me know if these ideas are of interest to you!

-- Keith

---------------------------------------------------------------
Keith Ball, Dill Group
Department of Pharmaceutical Chemistry
University of California at San Francisco
3333 California Street, Suite 415
San Francisco, CA 94118-1944

 phone: (415) 476-8910         fax: (415) 502-4222
e-mail: [email-masked]  http://rainbow.uchicago.edu/~kdb1
---------------------------------------------------------------
================
#7
Maybe I am saying something stupid, but Is it a solid cluster? If it was
solid, and maybe even if not, it would be interesting if there is a
structural model that could account for this, more than the number of
molecules (like in the C60) the possible structures accompanying the
number. At this respect, I would initially, advice, classical mechanic
codes since this is are ionic ions parametrized in literature and the
gain
in speed would allow the calculation of many geometrical configurations
in
a reasonable time, i.e. 200 atoms it is not an issue for these codes. As
well, as the use of some structure determination experimental
techniques,
neutron Diffraction, for instance. 

        I hope it helps, regards

                Manuel

ps Sorry if I say some nonsense, but you don't give much information in
the mail, and I am still under the flu influence, :-)
[All suggestions are very welcome--EL]
___________________________________________________________________
Manuel Melle Franco  -Ph.D. Student-

Dipartimento di Scienza dei Materiali
Universita' degli Studi di Milano-Bicocca
via Cozzi, 53 - 20125 Milano ITALY
Tel. Office (+39)-02-6448 5232
Tel. Home   (+39)-02-6610 2542
Fax.        (+39)-02-6448 5403
___________________________________________________________________

========
#8
 Dear Dr. Lewars,
      I think that you need to do statistical mechanical simulation for
your
 system since there would be enormous number of isomers for such a large
 system. Depending upon the temperature of the experiment several
isomers
 might have contributed to the specrtra ( for a similar problem in the
case
 of Si-C clusters ( even with a very small system compared to yours)
see,
 JPC A, 103, 1999, 6442). 
               Pradipta
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#9

Dear Dr. Lewars,

the mono-anionic Clusters are known. Have a look into
T.P. Martin, Physics Reports 95, 167 (1983)

However, there is currently a search for small di-anions,
and so far the "smallest" detected species are BeF4(2-) and
MgF4(2-). I would be very interested to know if your
colleague sees any evidence for KCl3(2-) or K2Cl4(2-).

Sincerely yours,
Thomas Sommerfeld

------------------------------------------------------------------------------
Dr. Thomas Sommerfeld                                   Tel:   +49 6221
545264
Theoretische Chemie, Universitaet Heidelberg            Fax:   +49 6221
545221
Im Neuenheimer Feld 229, 69120 Heidelberg, Germany         
Email: [email-masked]

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