Subject: Re: CCL:Which ab initio program is better?

From: <[email-masked]>
Date: Thu, 09 Jun 1994 16:09:26 -0500 (CDT)

Hi,

	We have done quite well with GAMESS (Iowa State version) and transition
metals, but that is not to say it is better than G92 (or GAMESS-UK or MOLPRO 
or...).  That's an argument that would generate much more heat than light. 
After all, what does 'better' mean anyway?  If you can do good science with a
program that is better. 
	I am almost certain the maximum number of atoms is 500.
	We have looked at very few radical TM complexes; they are 
notoriously difficult (first row metals will probably add to the complication).
However, we have been able to achieve good results for TM complexes incorporat-
ing metals from all three series and with MG elements from light to heavy using
GAMESS-US.
	Some advantages (in our somewhat biased opinion and based on
experience) of GAMESS-US for TM systems are as follows:
	1) The ECPs of Stevens et al. are built in.  These come 'out of the
box' sufficiently flexible in the valence basis set for most purposes.  Of
course, the  Hay-Wadt and most other ECP schemes can be read in to GAMESS and
most other programs will allow the SBKJ ECPs to be read in.
	2) Having open-shell and TMs (first-row to boot) is
almost begging for poor convergence behavior, and this is a real problem that
needs to be addressed before getting down to chemistry.  The initial guess 
routine in GAMESS was written a few years ago and is a champ. Based
on our experience, when it fails to give good convergence behavior it is
usually due to a very poor initial guess geometry.  I have not used any other
software in years, but I would imagine that up to date convergence accelerators
exist in other programs.  
	3) Runs on a bunch of parallel platforms!  If you are fortunate enough
to beg, borrow or steal time on a parallel supercomputer (preferably not the
latter alternative!) and have a problem that uses parallel algorithms then you
definitely want to explore this option.  GAMESS-US is quite easy to install; as
my students are fond of saying, it is so simple even Tom can do it!
	4) It's free!  Can't beat that wth a stick as we say in the South.
You can get it from the Iowa State folks by e-mail.

Tom
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Thomas R. Cundari                         
Asst. Professor of Chemistry              
Computational Inorganic Chemistry Lab     
University of Memphis                     Check out Univ. of Memphis
Memphis, TN 38152                         Chem Dept. on the World Wide Web
phone: 901-678-2629                       Organized by Prof. Henry Kurtz
fax:   901-678-3447                       Suggestions? [email-masked]
e-mail: [email-masked]
http://www.memst.edu/chemistry/umchem.html
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