Subject: imagin frequency & TS search

From: Krzysztof Radacki <[email-masked]>
Date: Wed, 07 Jul 1999 15:51:46 +0200

HI all,
I'm a little confused. 

Actualy I'm calculating reaction path where in last steo hydrogen is
shifted between two borons: A & B. 

I found local Min(1) with hydrogen on A-atom (g9* log:
   SCF Done:  E(RHF) =  -106.086888589     A.U. after   14 cycles
   Low frequencies ---  -18.2607   -5.9591    0.0007    0.0008   
0.0009    3.7707
   Low frequencies ---  132.6392  164.4866  455.8743)
Transition state which points on it has hydroge a little shifted in
direction of B-atom (log:
   SCF Done:  E(UHF) =  -106.086219321     A.U. after   13 cycles
   Low frequencies --- -233.5116   -8.0197   -3.0854    0.0006   
0.0010    0.0010
   Low frequencies ---    1.2505  325.0280  496.2008). Frequence -233.5
is conected to further shift of H in direction of B-atom. 
When from this TS(1) I started IRC calculation I got (what I suspected)
in one direction Min(1) in other Min(2). For this second minimum
Freq-part of log looks like:
   SCF Done:  E(UHF) =  -106.100979851     A.U. after   13 cycles
   Low frequencies --- -267.2175  -61.0431   -0.0010   -0.0008   
0.0006   26.4452
   Low frequencies ---  321.8358  344.4124  608.7472
so in  vibrational part Gaussian writes that the lowest frequency of
vibration is 321.8... Also here this freq=321 points further at
translation of hydrogen.
Because I don't specialy like rot.freq=-261 I started for Min(2) once
more optimalization, trying both opt=tight and opt=verytight. results
were very similar. What I got is geometry which has nothing to do with
Min(2) but with end-product of this reaction Min(End). 
Coming to my confusion. I copied from log-file first six geometries
found by SCF-steps and calculated freq.anal.
Parts of first 3 logs are below:
======== Min(3)
 SCF Done:  E(UHF) =  -106.111693951     A.U. after   13 cycles
...
 Low frequencies --- -253.8169  -83.3521   -0.0005    0.0007    0.0008  
46.3181
 Low frequencies ---  193.3072  346.7127  448.5709
 Harmonic frequencies (cm**-1), IR intensities (KM/Mole),
 Raman scattering activities (A**4/AMU), Raman depolarization ratios,
 reduced masses (AMU), force constants (mDyne/A) and normal coordinates:
                     1                      2                      3
                    A'                     A"                     A'
 Frequencies --   185.2393               344.2092               448.2177
======== Min(4)
 SCF Done:  E(UHF) =  -106.120239108     A.U. after   13 cycles
...
 Low frequencies --- -425.0755 -179.1839  -99.7147   -0.0009   -0.0008  
-0.0008
 Low frequencies ---  139.1175  299.3142  484.2108
 Harmonic frequencies (cm**-1), IR intensities (KM/Mole),
 Raman scattering activities (A**4/AMU), Raman depolarization ratios,
 reduced masses (AMU), force constants (mDyne/A) and normal coordinates:
                     1                      2                      3
                    A'                     A"                     A"
 Frequencies --    40.5275               287.4488               473.4673
======== Min(5)
 SCF Done:  E(UHF) =  -106.123411791     A.U. after   13 cycles
...
 Low frequencies --- -205.9984  -65.3112   -0.0004    0.0005    0.0007  
78.8174
 Low frequencies ---  288.0438  323.8774  433.4241
 Harmonic frequencies (cm**-1), IR intensities (KM/Mole),
 Raman scattering activities (A**4/AMU), Raman depolarization ratios,
 reduced masses (AMU), force constants (mDyne/A) and normal coordinates:
                     1                      2                      3
                    A'                     A"                     A"
 Frequencies --   287.1555               299.3749               431.4945
=========

As one can see both Min(1) and TS(1) have nearly the same energy however
difference in geometry is quite big.
What is funny is that this some points that I found through
reoptimalization of Min(2) (I labeled them Min(3)--Min(5)), however they
have very big forces, are found to be minima with frequence analysis.
What I disslike is that they have quite low rotational frequence. Also
what I realy disslike that I can't realy find any TS which leads from
Min(2) to Min(End). Even if I found such geometry that freq.analysis
shows one negative frequency connected to shift of hydrogen I'm
fninishing in both forward & reverse direction in Min(End).

What I thing is that gradient of energy between Min(2) and Min(End) can
be to small to find it with freq.analysis.
Another idea I want to try is changing level of theory to higher but I
realy appreciate any comments and advices.

Regards 
Krzysztof Radacki