Subject: Summary: Gamess - Trudge keyword

From: [email-masked] (Frederic BOUYER)
Date: Wed, 28 Jun 1995 17:04:12 +0100

Hello,

I'll sum up replies about the TRUDGE keyword in Gamess.

Special thanks are due to Dr. David Heisterberg and Dr. Brett Bode for our
fruitful discussions.

==============================================================================
>From Dr. Brett Bode:

Hello,
   The trudge keyword activates a Direct Energy minimization mechanism for
optimizing geometries. What this means is the GAMESS takes many small steps
along each degree of freedom for the geometry and then chooses the one
resulting in the lowest energy. This method requires many more geometry
points to find a minimum, but it does not require analytic energy derivatives,
and thus can be used when the analytic derivatives are unavailable (as is
the case for MP2 in GAMESS) or when the analytic derivative requires to
much disk or memory.
   I should stress that the Trudge method is very expensive in terms of
CPU time. In fact it is probably only realistic to optimize 2-5 degrees
of freedom with this method (freezing the others). But it is the only way
to do MP2 optimizations in GAMESS at the moment. Several other codes do
allow MP2 gradients such as Gaussian and others...

Brett

==============================================================================
>From Dr. David Heisterberg:

TRUDGE is a non-gradient method.  It's limited to optimizing 10
parameters, so it can only work for small molecules.  But then
it's very slow so you wouldn't want to use it for anything
large.  It is the only method for MP2 and CI for which analytical
gradients are not available.  It's really not recommended for
geometry optimization.  Rather, it's better suited for optimizing
exponents for a contracted basis.

Dave Heisterberg

==============================================================================
>From Will McCarthy:

>From: [email-masked] (Frederic BOUYER)

>Dear Netters,

>I was wondering what the keyword TRUDGE (optmiz=geometry) precisely means
>in Gamess, and how this optimizer works for obtaining a structure at the
>HF/MP2 level.

>Is it the only way to optimize a structure at the MP2 level?

I'm not personally familiar with the GAMESS program package, but the
TRUDGE keyword most probably refers to a Powell-Fletcher type algorithm
to be employed for geometry optimization.  This algorithm adjusts
each parameter (i.e. internal coordinate for a geometry optimization)
individually, then repeats the procedure until self-consistent.  The
advantage is that there is no need for the gradient, or hessian.
However, it is very slow.
Good luck, Will McCarthy
==============================================================================
>From Patrick Bultinck:

On Wed, 21 Jun 1995, Frederic BOUYER wrote:

> Dear Netters,
>
> I was wondering what the keyword TRUDGE (optmiz=geometry) precisely means
> in Gamess, and how this optimizer works for obtaining a structure at the
> HF/MP2 level.
>

Have a look at REFS.DOC, I believe it is described there.

> Is it the only way to optimize a structure at the MP2 level?

It is. The number of parameters that can be optimized at the same time is
restricted to 10 !

>
> Thank you for responding.
>
> Frederic Bouyer
> Lab. Electrochimie et Chimie Analytique, Paris - France
> [email-masked]
> http://alcyone.enscp.jussieu.fr/Pages/LECA/GP/FB/
>
>
>

Patrick

University of Ghent, Belgium
===============================================================================

*************************************************************
* Frederic Bouyer                                           *
* Lab. Electrochimie et Chimie Analytique, Paris - France   *
* [email-masked]                                     *
* http://alcyone.enscp.jussieu.fr/Pages/LECA/GP/FB/         *
*************************************************************