Subject: Summary of minimization w/COSMO

From: "Victor M. Rosas Garcia" <[email-masked]>
Date: Wed, 9 Aug 1995 20:25:59 -0400

Hi there,
	Sorry this summary is a little late.  My original posting was:
________________________________________________________________________________
Hi CCL'rs,
	I'm currently minimizing some molecules in MOPAC93, using a dielectric
constant of 78.3.  Mi starting point is the structure optimized in gas phase
using MOPAC 6.0.  After the run is finished I get the message:

"THE LINE MINIMIZATION FAILED TWICE IN A ROW.  TAKE CARE!"

And the GRADIENT NORM varies between 2 and 25 (a little too high, I think).

This are the keywords I'm using:

AM1 EPS=78.3 NOINTER T=3600.00 PRECISE

I have looked up in the list of error messages provided in the MOPAC 93 manual
but the message is not there.  Is this something to be concerned about?  Should
I be concerned about the gradient norm?

Any help will be appreciated.
________________________________________________________________________________

I received a few answers, and basically the recommendations were:

1) Take the output geometry and use it as input for another run.
   (I have done it and it usually works, but it can be tedious at times)
2) Use EF instead of BFGS and specify GNORM=0.01
3) Use keywords NODIIS and XYZ
4) Modify the code to stop after the average deviation of the delta Hf over the
    last five cycles is < 0.1 Kcal
5) In addition to EF, specify LET and DDMIN=0.0
6) Perturb one of the original parameters, let's say stretch a bond length by
      0.15 ang so that the optimizer will have a chance to get a good Hessian.
7) Do not be concerned about the gradient norm as long as it is less than 2.

Thanks to the CCL and specially to:

Jaime Combariza
Steve Bowlus
Andrew T. Pudzianowski
John McKelvey
Stanislaw Oldziej
and
Dave Giesen

Victor

PS. Somehow I think I'm missing ONE name.  I can't find it.  Sorry.