Mopac Lives !!



 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 #*at*# 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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