From chemistry-request@ccl.net Thu Aug  6 20:35:20 1992
Date: Thu, 6 Aug 92 14:44:39 -0400
From: rafael@ferry.polymer.uakron.edu (Rafael Garcia-Ramirez)
To: CHEMISTRY@ccl.net
Subject: Mopac Lives !!
Status: R


Guys:

	I have been using Mopac 6.0 for a while now (and I guess
I've learned to love it). Nevertheless, there is a particular WARNING
message that has always intrigued me. An example of such message, taken
from the output ( .out) file is as follows:

-----------------------------------------------------------------------
 AM1 EF PRECISE NOINTER
 /tmp_mnt/home/eby/rafael/sybyl/pbo/pbo2bend2.dat
 " "


     GEOMETRY OPTIMISED USING EIGENVECTOR FOLLOWING (EF).     
     SCF FIELD WAS ACHIEVED                                   


                                AM1    CALCULATION
                                                       VERSION  6.00
                                                       05-Aug-92               

          FINAL HEAT OF FORMATION =        145.40820 KCAL


          TOTAL ENERGY            =      -5879.16684 EV
          ELECTRONIC ENERGY       =     -43266.97471 EV
          CORE-CORE REPULSION     =      37387.80787 EV

 WARNING -- GEOMETRY IS NOT AT A STATIONARY POINT
          IONIZATION POTENTIAL    =          8.90687
          NO. OF FILLED LEVELS    =         85
          MOLECULAR WEIGHT        =    470.443


          SCF CALCULATIONS  =               92
          COMPUTATION TIME = 27 MINUTES AND  15.990 SECONDS

-----------------------------------------------------------------------

	I have noticed that this "error" appears sometimes, however
exclusively, when a certain geometrical constraint(s) has been
placed in the input Z-matrix [thus the geometry optimization is carried
out for every atomic coordinate, except for the one(s) corresponding to
the given constraint]. I understand that the minimizers in Mopac may not
always find the "global minimum" in energy (heat of formation) when the
constraint means a significant disturbance from the equilibrium geometry
and, therefore, such a message would be likely to appear. However, some-
times the minimum found clearly corresponds to a "true" minimum in energy
state (judging by the perfectly smooth trend observed in the ENERGY-vs-
CONSTRAINT VALUE curve) and the message still appears !! ...

	Can somebody PLEASE comment on the possible implications behind this 
and / or a possible way to fix it  ??.

	You can answer directly to me or, if it's easier (I'm ready to 
accept any public remarks about my IGNORANCE ), to the board.


	Thanks a lot ....



  



                                                  Rafael G. Ramirez
  ------------------------------------------------------------------
  email : rafael@eby.polymer.uakron.edu       phone:  (216) 972-5810
  usmail: Institute of Polymer Science        FAX  :  (216) 972-5290
          The University of Akron,  
          Akron, OH 44325-3909
          U.  S.  A.
  ------------------------------------------------------------------



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