Subject: Large Energy Jump in G98

From: "Chad Risko" <[email-masked]>
Date: Thu, 9 Jan 2003 10:06:55 -0700

Greetings!

I have just recently experienced with Gaussian98 (A.11) a rather strange
phenomenon in the optimization of two relatively large systems (roughly 8
and 9 benzene rings, respectively) and was wondering if anyone else had
dealt with a similar situation.  The two systems are being optimized with
b3lyp/6-31g* and, as can be seen from the data below, experience a rather
dramatic jump on the potential surface before the calculation 'dies':

system 1
 ....
 SCF Done:  E(RB+HF-LYP) =  -2650.61985735     A.U. after   21 cycles
 SCF Done:  E(RB+HF-LYP) =  -2650.62040110     A.U. after   12 cycles
 SCF Done:  E(RB+HF-LYP) =  -2650.62085039     A.U. after   12 cycles
 SCF Done:  E(RB+HF-LYP) =  -272.331239212     A.U. after   65 cycles

system 2
 ....
 SCF Done:  E(RB+HF-LYP) =  -2959.08379965     A.U. after    9 cycles
 SCF Done:  E(RB+HF-LYP) =  -2959.08380915     A.U. after   10 cycles
 SCF Done:  E(RB+HF-LYP) =  -2959.08383462     A.U. after   11 cycles
 SCF Done:  E(RB+HF-LYP) =  -1425.06108568     A.U. after   65 cycles

If anyone has a potential answer as to why such a large jump would occur
and/or how to try to prevent such a phenomenon in the future, I would
greatly appreciate it.  I will post any interesting replies.

Thanks for the assistance.

Regards
Chad

As well, here is the input that I utilized to define the calculation:

#P b3lyp/6-31g*
   GFInput  IOP(6/7=3) 6D 10F POP=full GFPRINT
   IOP(99/14=1)
   Opt(gdiis)

******************************
Chad Risko
Graduate Student
Bredas Research Group
Department of Chemistry
The University of Arizona
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