G:Sn2-reaction

From: Krzysztof Radacki <Krys.Radacki()at()ac.rwth-aachen.de>
Subject: G:Sn2-reaction
Date: Sat, 06 Jun 1998 20:54:28 +0200
 Hi CCL'ers.
 I'm trying to calculate TS for one Sn2 reaction. As starting point I used
 A-B..C
 where A-B was optimised as adduct and C as pure substance.
 As I know product is A..B-C (known from molecular dynamics in best chemical
 computer called "Schlenk-flask with periodic-box 25 ml filled with n-pentan
 molecules, run time 5 min").
 I've tried to change primary distance B...C but what I'm becoming is
 A-B..C with very big B..C distance or if B..C was short A..B-C with veeeery
 long A..B distance.
 What I've tried was three jobs:
 1.   opt=(z-matrix,TS)
  answer:
     -- Wrong number of Negative eigenvalues: Desired=  1 Actual=  0
 2.   opt=(z-matrix,Saddle=2)
  answer:
     -- Wrong number of Negative eigenvalues: Desired=  2 Actual=  0
 3.   opt=(z-matrix)
  answer:  after useing all possible steps how I wrote above one of two A..B
 or B..C distances going in direction infinity
  Maximum Force            0.000143     0.000450     YES
  RMS     Force            0.000076     0.000300     YES
  Maximum Displacement     0.248104     0.001800     NO
  RMS     Displacement     0.044904     0.001200     NO
 Can somebody tell me how to make Gaussian to do it?
 thanks in advance
            Krzys Radacki
  _________________________----------------------------------------------------
  -------------------------   e-mail:       Krys.Radacki()at()ac.RWTH-Aachen.DE
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