Subject: CCL: Summary, Trivial question

From: Albeiro Alonso Restrepo Cossio <[email-masked]>
Date: Sat, 24 Feb 96 13:54:32 -0500

Dear CCL subscribers,

Many thanks to all of you who spent some of your time in answering my question 
about the biggest system optimized ab initio methodologies ad the biggest water 
cluster optimized with simulated annealing; here is my summary.

Albeiro Restrepo.

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From: [email-masked] (cachau)

Hola Albeiro,

	Vi tu pregunta en el CCL y me arriesgo a darte mi opinion. Creo que
tendras serias dificultades en encontrar una respuesta a tu pregunta. La 
razon es que necesitas una definicion operativa de "mas grande". Si te fijas
en "numero de atomos" puedes elejir una pequenya base y de este modo puedes
calcular moleculas muy grandes. Si en cambio prefieres usar como parametro el
numero de bases, entonces te encuentras con que hay sistemas diatomicos que
se han tratado con muchos cientos de bases y con bases de simetria mas alta
que g lo que es inconcebible de usar para una molecula de interes biologico,
de modo que siguiendo este criterio llegarias a la conclusion de que una
molecula diatomica con algun atomo pesado seria tal vez el sistema mas grande
nunca tratado a nivel HF. Entonces, ni el numero de bases ni el numero de 
atomos constituyen tu definicion. Por si esto no fuera ya complejo, luego
tienes que incorporar el problema de optimizacion: HF sin optimizar
es un problema, optimizada la estructura es un orden de magnitud mas grande
como problema, y si llegas a caracterizar la geometria (calcular su Hessiano) 
es un orden de magnitud mas alto aun. En la complejidad del problema, como
incluyes la simetria?. Hay ENORMES complejos con piridinas resueltos con 
bases enormes pero con simetria altisima. Que "tamanyo" le asignarias al
complejo?. Que tan grande te resulta un buckyball?. 60 atomos o 5 + simetria?.
Y luego tienes los calculos 'a la Clementi (posiblemente en mi criterio los
mas grandes nunca hechos en biomoleculas) en su famoso "Star" system. El 
usaba bases muy grandes, pero usaba una "base asociada" a largas distancias
de modo que se ahorraba de calcular un numero altisimo de integrales de este 
modo, como medirias la complejidad en este caso?.

En fin, que no te he resuelto tu pregunta, sorry, pero creo que necesitas 
darle una pulida a tu definicion si quieres que la respuesta sea "meaningful".

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From: Kris Van Alsenoy <[email-masked]>

Dear Albeiro,

In response to your question concerning molecular clusters, I would 
like to mention the following papers :

Anik Peeters, C. van Alsenoy, A.T.H. lenstra, H.J. Geise,
Int. J. Quant. Chem., Vol. 46, 73-80 (1993)

C. Van Alsenoy, Anik Peeters,
J. Mol. Struct., Vol. 286, 19-34 (1993)

Anik Peeters, C. Van Alsenoy, A.T.H. Lenstra, H.J. Geise,
J. Mol. Strcut., Vol. 304, 101-107 (1994)

Anik Peeters, C, Van Alsenoy, A.T.H. Lenstra, H.J. Geise,
J. Chem. Phys., Vol. 103, 6608-6616 (1995)

In thes epapers we studied a number of molecules using a cluster approach.
Is this what you were looking for ?

Sincely,

  kris van alsenoy
  [email-masked]

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From: "E. Lewars" <[email-masked]>

Albeiro Restrepo asked about the biggest systems that have been studied by
ab initio, and the reliability of the results. I don't claim that these are the
biggest anyone has looked at, but they are at the high end of ab initio jobs:

(1) MP2(FC)/6-311G** (312 basis funtions) on  C6H5-C:::C-C6H5: S. Saebo and
    J. Almlof et al, THEOCHEM 59, 361 (1989).
(2) MP2/6-31G* optimizations on porphyrins, ca 20 heavy atoms. At the MP2 level,
    unlike the HF, the known, dampened bond alternation characteristic of these
    aromatic systems is evident. _Long_ calc's. See L. Paquette et al, ca. 1995
    (J Am Chem Soc?).
(3) For a short, very useful review of work on ab initio etc calc's and their
    reliability, see I. N. Levine, _Quantum Chemistry_, 4th Ed., Prentice Hall,
    1991, Chapters 15, 16, 17.

  Errol Lewars

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From: Artem Masunov <[email-masked]>

Dear Albeiro Restrepo,
	We did HF optimization of some supermolecular clusters containing
up to 80 atoms. They are not published yet. 
	If you find bigger system being optimized, please let me know.
Regards,
Artem

> Does someone in the list have information about the bigest system succesfully
> optimized by any ab initio methodology and about its reliability? 

      __   _________ 
     /  \ /  _   _  \   Artem Masunov - [email-masked]
    /    \\  \\  \\  \       Chemistry Department, Hunter College
   /  /\  \\  \\  \\  \          City University of New York
  /  ____  \\  \\  \\  \     695 Park Avenue, New York, NY 10021
 /__/\__/\__\\__\\__\\__\ Tel: (212) 725-0317, Fax: (212) 772-5332
 \__\/  \/__//__//__//__/
I know you believe you understand what you think I said, but I am not sure
you realize that what you heard is not what I meant. (Gaussian92)

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From: Artem Masunov <[email-masked]>

On Mon, 19 Feb 1996, Albeiro Alonso Restrepo Cossio wrote:

> Does your group have any intention of publishing that results?

Yes, mixed hexamer of melamine-barbituric acid will be reported on 
ACS meeting this spring, urea decamers were reported on ACA meeting last 
summer (see abstract on WWW):
http://www.cisti.nrc.ca/programs/ACA95/M/a429.html

Papers will be submitted to one of ACS journals in a few month.

Regards,
Artem

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From: "Dr. James Brown" <[email-masked]>

On Feb 19, 12:17pm, E. Lewars wrote:
> Subject: CCL:BIG AB INITIO JOBS

> (1) MP2(FC)/6-311G** (312 basis funtions) on  C6H5-C:::C-C6H5: S. Saebo and
>     J. Almlof et al, THEOCHEM 59, 361 (1989).

A study of glucose by us in JACS coming out soon had 348 basis functions.
 Another on glucose conformers by Truhlar and coworkers to be published in
Carbohydrate Research included 624 basis functions.  As far as
reliability...it's difficult to tell since there's not much data on glucose in
the gas phase.

James

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From: Artem Masunov <[email-masked]>

Dear Albeiro Restrepo,
Since CCLers started to count basis functions, I can tell, that urea 
decamer had 840 basis functions (D95**). Mixed hexamer had 
918 basis functions (D95*) and will be presented at Symposium 
Semiempirical methods: Do they have a future? 
in New Orlean (March 1996) by Prof. J.J.Dannenberg.
 Artem

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From: Kris Van Alsenoy <[email-masked]>

Dear Albeiro,

I forgot to mention a study on sugars using TZV & TZVP -basisets :

C. Van Alsenoy, A.D. French, M. Cao, S.Q. Newton, L. Sch"afer,
JACS, Vol. 116, 9590-9595 (1994)

sincerly,
   kris

On Mon, 19 Feb 1996, Albeiro Alonso Restrepo Cossio wrote:

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From: [email-masked] (Juha Muilu)

Hi,

I have done some ab initio calculations on  ZnS clusters up to 

Zn240S240 (1200 basis functions & 6000 primitive functions). 

The calculations are made possible using translational 

properties of finite clusters. What comes to reliability I 

must say that the models are rather academic....

For more information: 

http://www.chem.joensuu.fi/people/juha_muilu/Research/zns_clusters.html
Also from Surf.Science during this year, I hope.

----
 Juha Muilu
 Department of Chemistry,University of Joensuu,P.O. Box 111
 80101 Joensuu,FINLAND/Email:[email-masked],Phone:358-73-1513312,
 Fax:358-73-1513390,http://www.chem.joensuu.fi/people/juha_muilu

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From: Stuart Watson <[email-masked]>

Hi,

Our current record is performing molecular dynamics on 6700 Na atoms,
using an "Order-N" DFT method (for the initial article see M. Pearson et
al, J. Phys. Cond. Matter, 5, 3321 (1993). The method is only really
applicable to systems with delocalised electrons (ie metals), and reproduces
Kohn-Sham results for alkali metals.

This system was run on a Cray T3D (timing on 128nodes 9s electronic, 
1200 ionic - thats the benefit of an Order-N method), and it is feasible
to probably quadruple the no. of atoms (as the memory requirements, as
well as the time scales linearly).

Stuart Watson

##########################################################################
#  Stuart Watson                    #  Life is like a box of chocolates, #
#  [email-masked]         #  it gets all squishy when dropped  #
#  http://physchem.ox.ac.uk/~stuart #  from a great height.              #
##########################################################################
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From: Bryan Marten <[email-masked]>
Zhang and Friesner recently reported Self Consistent Reaction Field (QM
solute surrounded by continuum dielectric solvent requiring several
converged HF wavefunctions) calculations at the HF/6-31G** level for
bacteriochlorophyll and bacteriopheophytin on an IBM RS/6000 workstation
using the electronic structure program PSGVB in JPC 99 16479 1995.
Those were in the 880-890 basis function range on molecules with C1 (no)
symmetry and are believed to be the largest SCRF ab inito calculations
to date.  The authors use the SCRF calculations to compute redox
potentials in DMF, compare to experiment, and report qualitative
agreement for relative redox energies.
-- 
				Dr. Bryan Marten
				Ciba Pharmaceuticals
				[email-masked]

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From: "Schiffer, Heinz, Dr." <[email-masked]>

Sometime ago someone asked for references to large ab initio calculations ( 
sorry, but I forgot who it was ). I just got a copy of a paper of Gustavo 
Scuseria at Rice University in Houston who did a Hartree-Fock geometry 
optimization within icosahedral symmetry for a fullerene with 540 atoms and 
with 2700 basis functions on a single IBM RS6000 workstation. The program he 
used was TURBOMOLE  from Ahlrichs' group in Karlsruhe.

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