Subject: How to increase max number of geometry optimization steps in G98?

From: Scott McMillan <[email-masked]>
Date: 16 Dec 1999 23:46:07 -0600

Hello,

I'm performing pm3 geometry optimizations in Gaussian 98 on systems
with some atoms fixed at their cartesian position. I'm using the
keyword opt=z-matrix to fix these atoms. Some of my calculations do not
have enough geometry iterations to complete.  From the G98 manual, it
appears that setting iop(1/6=N) should set the maximum number of
geometry optimizations to N. However, G98 seems to have some other
maximum setting as well. The manual also suggests that opt(maxcycle=M)
would have a similar effect as iop(1/6), but it appears to do nothing.

For example, from my output:
 Number of steps in this run= N maximum allowed number of steps= 204.

I can set N to any value less than or equal to 204 with iop(1/6), but
not larger.  How do I increase the second value above 204?  The 204
value depends on the system (# degrees of freedom); there's nothing
special about that particular number.

I know I can save the checkpoint file and then keep restarting the
calculation, but I'm looking for a solution that won't require this
level of manual intervention.

Thanks,
Scott
--
Scott McMillan - [email-masked] - http://winnie.chem-eng.nwu.edu/~scott/
Institute for Environmental Catalysis
Department of Chemical Engineering
Northwestern University

---

From: "C.F. Matta" <[email-masked]>
Date: Fri, 17 Dec 1999 11:06:06 -0500 (EST)

Hi Scott,

	Sometime ago I ran into the same problem. The number of
geometry optimization steps can be set to any value in Gaussian94 by a
command like:

          opt=(z-matrix, maxcycle=300) 

This does work in G94, I do not know if it it the same with G98, but you
can try it.

Take care.

Cherif
.......................................................................
 Cherif F. Matta		  	tel. (905) 525-9140 ext. 22502
 Chemistry Department                   fax  (905) 522-2509
 McMaster University                      
 Hamilton, Ontario, CANADA L8S 4M1.
.......................................................................

On 16 Dec 1999, Scott McMillan wrote:

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