RE: G03 optimization failure

Jim,
 Some suggestions:
 1. Check the final geometry of the optimization in your favorite viewer.
 Perhaps something unexpected has happened, such as the molecule breaking up into
 two fragments.
 2. If the geometry is OK try using "geom=check opt=calcfc".  This will
 fix any problems related to the Hessian (2nd derivative matrix).
 3. If your radical has symmetry, try breaking the symmetry (usually this can be
 done by changing a torsion angle by 5-10 degrees) and reoptimizing.
 Hope this helps,
 --David Shobe, Ph.D., M.L.S.
 S|d-Chemie, Inc.
 phone (502) 634-7409
 fax (502) 634-7724
 Don't bother flaming me: I'm behind a firewall.
 -----Original Message-----
 From: Computational Chemistry List [mailto:chemistry-request=at=ccl.net]On
 Behalf Of Jim Pfaendtner
 Sent: Wednesday, August 11, 2004 10:49 AM
 To: chemistry=at=ccl.net
 Subject: CCL:G03 optimization failure
 Hi,
 I'm trying a simple geometry optimization in G03 , it is a C4
 hydrocarbon with a carbonyl group and peroxy radical.  I'm using
 ub3lyp/6-31g*
 The thing runs for awhile and then I get this error message:
  Linear equations converged to 1.310D-10 1.310D-09 after  10 iterations.
  Search did not lower the energy significantly.
  No lower point found -- try reversing direction.
  Search did not lower the energy significantly.
  No lower point found -- switch to scaled steepest descent.
  Search did not lower the energy significantly.
  Scaled steepest descent with Shift=0.000 failed.
  Search did not lower the energy significantly.
  Scaled steepest descent with Shift=0.025 failed.
  Search did not lower the energy significantly.
  Scaled steepest descent with Shift=0.050 failed.
  Search did not lower the energy significantly.
  Scaled steepest descent with Shift=0.075 failed.
  Search did not lower the energy significantly.
  No lower point found -- switch to steepest descent.
  Search did not lower the energy significantly.
  No lower point found -- run aborted.
 I have tried with and without SCF(qc) but that didn't help.  Do I need
 to change my tolerances? I also tried to first optimize using HF and a
 smaller basis set to get a guess for the geometry.
 Thanks!
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