Subject: Scanning

From: Genzo Tanaka <tanaka^at^ahpcrc.org>
Date: Thu, 13 Nov 2003 15:58:23 -0500

Hi,

I have a problem for relaxed scanning of torsion using PM3 in
Gaussian98. My molecule has about 90 atoms. A single torsion scanning
was successful. Scanning with two torsions has hardly optimized even at
the first point. More specifically, the first point, which should be the
starting structure since it had optimized before, could be obtained
occasionally, but then an error "incomplete coordinate system" occurred:

Incomplete coordinate system.  Try restarting with
 Geom=Check Guess=Read Opt=(ReadFC,NewRedundant)

Restart could optimize only a single point. I have tried both cartesian
and Z-matrix input format, and loosening the convergence criteria,
nothing helped at all.

A similar job with 50 atoms completed scanning all assigned
combinations.

Does anybody give me any suggestions how to overcome this problem?
My input file is attached below

Thanks,

Genzo

*** my input file ***

%nprocl=8
%Chk=conj1opttorscan
#P RHF/PM3 Opt=(ModRedundant,Loose) NoSymm GFINPUT IOP(6/7=3)
IOP(2/16=1)

conj1 Torsion Scanning 32-42-53-76-68 (120,180 original)

0 1
 C    -5.629806     0.277667     0.815136
 C    -6.673190    -0.814308     0.915021
 C    -8.103200    -0.395261     1.056532
....
 O     9.155696    -0.234578     2.974792
 N     5.137230     1.557668    -6.584475
 H     6.699645    -2.635203     0.905287
 H     7.066098    -2.208875     2.588433
 H     8.376042    -2.670414     1.489473

 * 42 53 * R
 32 42 53 76 S 5 60.0
 * 53 76 * R
 42 53 76 68 S 5 60.0