Subject: Locating a transition state

From: [email-masked]
Date: Fri, 26 Apr 2002 15:51:46 -0400

Hi,

I am trying to locate a transition state for a system about 30 atoms using 
an empirical
method. So far I haven't had any success. I would appreciate if you could
give me any suggestions. 

I am interested in a hydrolysis reaction pathway, using PM3 in Gaussian 
98:

R-C-O-C-R' + H*-O'H ---> R-C-O-H*  + H-O'-C-R'

I have done the following: 
1) opt=Ts ; This always failed due to incorrect number of negative
frequencies. 
2) Scan  ; I have not tried much. 
3) opt=ModRedundant: Scanning succeeded, but the population analysis after
the scanning seemed failed. The output did not indicate why it failed, but
the heading of population analysis appeared, followed by signal 11 error. 
4) opt=qst2; There is (are) one or two statement(s) "stationary point was
found" (the distances were the same for all, but the angles and torsions 
were slightly different in the two stationary points) in the output, but 
the optimization (?) kept going and failed; Optimization aborted
--- No acceptable step or Inconsistency: ModMin=   2. 

I optimized two reactant molecules individually and moved them close to 
make
a reaction. The products were also optimized. The order of the atoms are
exactly the same. 

Thanks, 

Genzo Tanaka 
Network Computing Services, Inc./ 
Army High Performance Computing Research Center at FAMU