Subject: Transition state search using MOPAC.

From: "Park, Tae-Yun" <[email-masked]>
Date: Tue, 9 Jul 1996 19:11:58 +0200 (DFT)

Dear all,

I need some help from people who uses MOPAC frequently,
as I'm a real beginner of using MOPAC.

I want to search the transition state(TS) of the following 
reaction with MOPAC93:

   H              H     H                       H H H
   |               \   /                        | | |
 H-C(+)       +     C=C     ---->(TS?)---->   H-C-C-C(+)
   |               /   \                        | | |
   H              H     H                       H H H

 gas-phase                                     gas-phase
   methyl         ethylene                   primary propyl
carbenium ion                                 carbenium ion

After reading the session of transition state location(SADDLE) 
in MOPAC manual, I have prepared the following input data for 
MOPAC:

***************************************************************

UHF  SADDLE DENSITY GRAPH XYZ CHARGE=1 BAR=0.03 
Me--->p methylation activated complex

 C     .000000 0     .000000 0     .000000 0       0    0    0
 H    1.113983 1     .000000 0     .000000 0       1    0    0
 H    1.113983 1  120.001495 1     .000000 0       1    2    0
 H    1.113968 1  119.999756 1 -179.453217 1       1    2    3
 C    5.210007 1  129.371857 1 -179.367538 1       1    2    3
 C    1.336975 1  114.626526 1   -2.741700 1       5    1    2
 H    1.099976 1  120.501572 1 -179.999634 1       5    6    1
 H    1.100006 1  119.749710 1 -179.453217 1       5    6    7
 H    1.099976 1  120.499832 1  179.999634 1       6    5    7
 H    1.099976 1  119.749710 1     .547287 1       6    5    7
 0    0.000000 0    0.000000 0    0.000000 0       0    0    0
 C     .000000 0     .000000 0     .000000 0       0    0    0
 C    1.506600 1     .000000 0     .000000 0       1    0    0
 C    1.418946 1  116.679237 1     .000000 0       2    1    0
 H    1.118213 1  111.091591 1  -60.563965 1       1    2    3
 H    1.119848 1  109.781792 1  179.985870 1       1    2    3
 H    1.118203 1  111.102783 1   60.532600 1       1    2    3
 H    1.150792 1  110.664017 1  174.500137 1       2    1    4
 H    1.150722 1  110.665337 1   64.389313 1       2    1    4
 H    1.109605 1  121.234596 1  179.993790 1       3    2    1
 H    1.110235 1  121.565987 1    -.003556 1       3    2    1
 0    0.000000 0    0.000000 0    0.000000 0       0    0    0

****************************************************************

The result with this input data was terrible; in the transition 
state, H2 and H were separated!

The data were prepared as follows:

1. I've drawn two reactants using CS Chem 3D Pro and save as 
   MOPAC input.  I could not optimize the geometry of these
   two molecules in MOPAC simulatneously, since there are two 
   molecules exist.

2. The data for the product carbenuim ions was prepared 
   with CS Chem3D Pro again, and the geometry of this 
   molecule was minimized with MOPAC keywards, 
    
      "SYMMETRY CHARGE=1 AM1 GEO-OK EF PRECISE"

   and then saved as an optimezed data for the product 
   carbenium ion.

3. Then I combined these two files and modified according 
   to the decription in the MOPAC manual for SADDLE 
   calculation.

4. And I've got the terrible result.

What's wrong with my input data for the SADDLE calculation?
Is it really possible to get the optimized geometry of 
transition state for the reaction I mentioned above by 
using MOPAC?  

If so, could anyone PLEASE tell me how I can get a reliable
structure of the transition state theoretically?

ANY suggestion/advice will be GREATLY APPRECIATED!

Thank you very much in advence.

				Sincerely,

				     Park, TAE-YUN    
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State University of Ghent
Laboratorium voor Petrochemische Techniek
Krijgslaan 281, Blok S5  
9000 Gent, Belgium	  
TEL:+(32)-0(9)-264-4527
FAX:+(32)-0(9)-264-4999
e-mail: [email-masked]
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