Subject: CCL:Control convergene threshold in Gaussian

From: Wayne Fisher <wfisher=at=utdallas.edu>
Date: Fri, 19 Sep 2003 11:30:46 -0500

Colleagues,

On 16 Sep 2003 Zhi-Xiang Wang wrote:

Date: Tue, 16 Sep 2003 09:51:20 -0400 (EDT)
From: Zhi-Xiang Wang <zxwang=at=sunchem.chem.uga.edu>
To: chemistry=at=ccl.net
Subject: CCL:Control convergene threshold in Gaussian

Hi
  Do we have a method to make the convergene threshold in Gaussian like
that

                                            Threshold
 Maximum    Force                    .000050
 RMS            Force                     .000300
 Maximum    Displacement       .018800
 RMS            Displacement        .012000

Instead of the default values

         Item                            Threshold
 Maximum    Force                    .000450
 RMS            Force                      .000300
 Maximum    Displacement        .001800
 RMS            Displacement        .001200

Thanks

Zhixiang

In a subsequent private communication he wrote:

   Unfortunately, I have't got the right answer for this question.
However I know we can use iop(1/7=mmm) to adjust the threshold. The
default value mmm=300. The problem for me is when I use smaller mmm,
both
the maxium and rms force and the maxium and rms displacement decrease,
instead of an increasing in maxium and rms displacement as I want. Hope
it
is useful for you.

ZX

Unfortunately it does not seem that these thresholds are independently
variable in Gaussian 03.  The variable for the RMS Force, ConvF, is set
by default to 3/10000 unless IOp(1/7) overrides the default.  In that
case IOp(1/7)=mmm sets ConvF and thus the threshold for RMS Force to
mmm/10000.  Also note that, according to the Gaussian 03 IOps Reference
manual, IOp(1/7=-1) sets ConvF to 1/600.

ConvX, the variable for RMS Displacement, appears to be hard coded as
ConvF*4, so the threshold for RMS Displacement will always be four times
that of the RMS Force.

Further, the variables for Maximum Force and Maximum Displacement are
set as follows:
Maximum Force = ConvF*CnvFMX
Maximum Displacement = ConvX*CnvFMX
and CnvFMX is set as data to 1.5.

Thus we always have the following relationships:

RMS Force = set by default or IOp(1/7)
Maximum Force = RMS Force*1.5
Maximum Displacement = RMS Force*6
RMS Displacement = RMS Force*4

Best regards,

Wayne Fisher
The University of Texas at Dallas