From chemistry-request@www.ccl.net Tue Jan 12 12:21:37 1999 Received: from mail.uni-muenster.de (MAIL.UNI-MUENSTER.DE [128.176.188.76]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id MAA08973 Tue, 12 Jan 1999 12:21:34 -0500 (EST) From: cml@uni-muenster.de Received: from fiasko (RAS21-195.UNI-MUENSTER.DE [128.176.234.196]) by mail.uni-muenster.de (8.8.7/8.8.7) with SMTP id SAA18616 for ; Tue, 12 Jan 1999 18:21:31 +0100 Message-Id: <199901121721.SAA18616@mail.uni-muenster.de> To: CHEMISTRY@www.ccl.net Date: Tue, 12 Jan 1999 18:19:10 +0100 Subject: mopac/fortran on different platforms Priority: normal X-mailer: Pegasus Mail for Win32 (v3.01b) Dear list members, I have been working with Mopac93 for quiet a long time and have obeserved the following problem on several occasions: Depending on the platform on which it has been compiled, different results are obtained when an optimization runs into numerical difficulties. I have compared the compiled programs which have been generated on the following systems: RS/6000 (AIX,xlf) - PentiumII (Linux,g77) - AMD K6/2 (Linux,g77) In those cases, where the geometry optimization (EF) runs straight into the energetic minimum, all three versions give nearly the same energy and geometry. In cases where the optimization demands a large number of steps, or when transition states are searched, the three versions tend to behave much more diverse. To give an example, in one case (TS with LET DDMIN=0.00) the two Linux binaries give an optimized geometry while the AIX version stops with a geometry 10 kcal lower in energy and repeating the warning "NUMERICAL PROBLEMS..". In another case (reaction path with three points for one dihedral angle) the AIX version ends without complaint while the Linux versions give the error message: CARTESIAN COORDINATES READ IN, AND CALCULATION TO BE RUN IN INTERNAL COORDINATES, BUT NOT ALL COORDINATES MARKED FOR OPTIMISATION although the input geometry IS a z-matrix in INTERNAL coordinates with some parameters marked to be held constant. This can only be overcome by adding XYZ to the input line, but then the two Linux version behave different: On the AMD K6/2, the calculation stops after 500 cycles without finding a minimum, on the PentiumII it works, but gives energies that differ from the AIX-results. This of course might be the result of the use of cartesian coordinates for optimization. To conclude this story, I would like to ask the following questions: 1) Has somebody of you already observed a similar behaviour of MOPAC- versions (or any other program) that have been ported to different plat- forms, and (if so) 2) is this due to the different CPU architectures or to the use of different compilers ? 3) What might be the problem with the internal coordinates that are not recognized as an internal z-matrix? Is this connected with the format in which the z-matrix is read in ? I am looking forward to helpful comments, sincerely Christian Mueck-Lichtenfeld ------------------------------------------------------------ Dr. Christian Mck-Lichtenfeld Organisch-Chemisches Institut Westf„lische Wilhelms-Universit„t Corrensstraáe 40 cml@uni-muenster.de D-48149 Mnster (Germany) phone +49 251 83-33239 ------------------------------------------------------------